zephyr/boards/openisa/rv32m1_vega/doc/index.rst

.. highlight:: sh

.. zephyr:board:: rv32m1_vega

Overview
********

The VEGAboard contains the RV32M1 SoC, featuring two RISC-V CPUs,
on-die XIP flash, and a full complement of peripherals, including a
2.4 GHz multi-protocol radio. It also has built-in sensors and
Arduino-style expansion connectors.

The two RISC-V CPUs are named RI5CY and ZERO-RISCY, and are
respectively based on the `PULP platform`_ designs by the same names:
`RI5CY`_ and `ZERO-RISCY`_. RI5CY is the "main" core; it has more
flash and RAM as well as a more powerful CPU design. ZERO-RISCY is a
"secondary" core. The main ZERO-RISCY use-case is as a wireless
coprocessor for applications running on RI5CY. The two cores can
communicate via shared memory and messaging peripherals.

Currently, Zephyr supports RI5CY with the ``rv32m1_vega/openisa_rv32m1/ri5cy`` board
configuration name, and ZERO_RISCY with the ``rv32m1_vega/openisa_rv32m1/zero_riscy`` board
configuration name.

Hardware
********

The VEGAboard includes the following features.

RV32M1 multi-core SoC:

- 1 MiB flash and 192 KiB SRAM (RI5CY core)
- 256 KiB flash and 128 KiB SRAM (ZERO-RISCY core)
- Low power modes
- DMA support
- Watchdog, CRC, cryptographic acceleration, ADC, DAC, comparator,
  timers, PWM, RTC, I2C, UART, SPI, external memory, I2S, smart
  card, USB full-speed, uSDHC, and 2.4 GHz multiprotocol radio
  peripherals

On-board sensors and peripherals:

- 32 Mbit SPI flash
- 6-axis accelerometer, magnetometer, and temperature sensor (FXOS8700)
- Ambient light sensor
- RGB LED
- microSD card slot
- Antenna interface

Additional features:

- Form-factor compatible with Arduino Uno Rev 3 expansion connector
  layout (not all Arduino shields may be pin-compatible)
- UART via USB using separate OpenSDA chip
- RISC-V flash and debug using external JTAG dongle (not included) via
  2x5 5 mil pitch connector (commonly called the "ARM 10-pin JTAG"
  connector)

Supported Features
==================

.. zephyr:board-supported-hw::

BLE Software Link Layer experimental support
==================================================
This is an experimental feature supported on the Zephyr's RI5CY
configuration, ``rv32m1_vega/openisa_rv32m1/ri5cy``. It  uses the Software Link Layer
framework by Nordic Semi to enable the on-SoC radio and transceiver for
implementing a software defined BLE controller. By using both the controller
and the host stack available in Zephyr, the following BLE samples can be used
with this board:

- beacon
- central
- central_hr
- eddystone
- hci_uart
- ibeacon
- peripheral_csc (Cycling Speed Cadence)
- peripheral_dis (Device Information Service)
- peripheral_esp (Environmental Sensing Service)
- peripheral_hr (Heart Rate)
- peripheral_ht (Health Thermometer)
- peripheral
- scan_adv

.. note::

   BLE Software Link Layer limitations:

   - no 512/256 Kbps PHY
   - no TX power adjustment


Connections and IOs
===================

RV32M1 SoC pins are brought out to Arduino-style expansion connectors.
These are 2 pins wide each, adding an additional row of expansion pins
per header compared to the standard Arduino layout.

They are described in the tables in the following subsections. Since
pins are usually grouped by logical function in rows on these headers,
the odd- and even-numbered pins are listed in separate tables.  The
"Port/bit" columns refer to the SoC PORT and GPIO peripheral
naming scheme, e.g. "E/13" means PORTE/GPIOE pin 13.

See the schematic and chip reference manual for details.
(Documentation is available from the `OpenISA GitHub releases`_ page.)

.. note::

   Pins with peripheral functionality may also be muxed as GPIOs.

**Top right expansion header (J1)**

Odd/bottom pins:

===   ========    =================
Pin   Port/bit    Function
===   ========    =================
1     E/13        I2S_TX_BCLK
3     E/14        I2S_TX_FS
5     E/15        I2S_TXD
7     E/19        I2S_MCLK
9     E/16        I2S_RX_BCLK
11    E/21        SOF_OUT
13    E/17        I2S_RX_FS
15    E/18        I2S_RXD
===   ========    =================

Even/top pins:

===   ========   =================
Pin   Port/bit   Function
===   ========   =================
2     A/25       UART1_RX
4     A/26       UART1_TX
6     A/27       GPIO
8     B/13       PWM
10    B/14       GPIO
12    A/30       PWM
14    A/31       PWM/CMP
16    B/1        GPIO
===   ========   =================

**Top left expansion header (J2)**

Odd/bottom pins:

===   ========   =================
Pin   Port/bit   Function
===   ========   =================
1     D/5        FLEXIO_D25
3     D/4        FLEXIO_D24
5     D/3        FLEXIO_D23
7     D/2        FLEXIO_D22
9     D/1        FLEXIO_D21
11    D/0        FLEXIO_D20
13    C/30       FLEXIO_D19
15    C/29       FLEXIO_D18
17    C/28       FLEXIO_D17
19    B/29       FLEXIO_D16
===   ========   =================

Even/top pins:

===   ========   =================
Pin   Port/bit   Function
===   ========   =================
2     B/2        GPIO
4     B/3        PWM
6     B/6        SPI0_PCS2
8     B/5        SPI0_SOUT
10    B/7        SPI0_SIN
12    B/4        SPI0_SCK
14    -          GND
16    -          AREF
18    C/9        I2C0_SDA
20    C/10       I2C0_SCL
===   ========   =================

**Bottom left expansion header (J3)**

Note that the headers at the bottom of the board have odd-numbered
pins on the top, unlike the headers at the top of the board.

Odd/top pins:

===   ========   ====================
Pin   Port/bit   Function
===   ========   ====================
1     A/21       ARDUINO_EMVSIM_PD
3     A/20       ARDUINO_EMVSIM_IO
5     A/19       ARDUINO_EMVSIM_VCCEN
7     A/18       ARDUINO_EMVSIM_RST
9     A/17       ARDUINO_EMVSIM_CLK
11    B/17       FLEXIO_D7
13    B/16       FLEXIO_D6
15    B/15       FLEXIO_D5
===   ========   ====================

Even/bottom pins: note that these are mostly power-related.

===   ========   =================
Pin   Port/bit   Function
===   ========   =================
2     -          SDA_GPIO0
4     -          BRD_IO_PER
6     -          RST_SDA
8     -          BRD_IO_PER
10    -          P5V_INPUT
12    -          GND
14    -          GND
16    -          P5-9V VIN
===   ========   =================

**Bottom right expansion header (J4)**

Note that the headers at the bottom of the board have odd-numbered
pins on the top, unlike the headers at the top of the board.

Odd/top pins:

===   ========   ========================================
Pin   Port/bit   Function
===   ========   ========================================
1     -          TAMPER2
3     -          TAMPER1/RTC_CLKOUT
5     -          TAMPER0/RTC_WAKEUP_b
7     E/2        ADC0_SE19
9     E/5        LPCMP1_IN2/LPCMP1_OUT
11    -          DAC0_OUT/ADC0_SE16/LPCMP0_IN3/LPCMP1_IN3
===   ========   ========================================

Even/bottom pins:

===   ========   ===========================================
Pin   Port/bit   Function
===   ========   ===========================================
2     C/11       ADC0_SE6
4     C/12       ADC0_SE7
6     B/9        ADC0_SE3
8     E/4        ADC0_SE21
10    E/10       ADC0_SE19 (and E/10, I2C3_SDA via 0 Ohm DNP)
12    E/11       ADC0_SE20 (and E/11, I2C3_SCL via 0 Ohm DNP)
===   ========   ===========================================

Additional Pins
---------------

For an up-to-date description of additional pins (such as buttons,
LEDs, etc.) supported by Zephyr, see the board DTS files in the Zephyr
source code, i.e.
:zephyr_file:`boards/openisa/rv32m1_vega/rv32m1_vega_openisa_rv32m1_ri5cy.dts` for RI5CY and
:zephyr_file:`boards/openisa/rv32m1_vega/rv32m1_vega_openisa_rv32m1_zero_riscy.dts` for
ZERO-RISCY.

See the schematic in the documentation available from the `OpenISA
GitHub releases`_ page for additional details.

System Clocks
=============

The RI5CY and ZERO-RISCY cores are configured to use the slow internal
reference clock (SIRC) as the clock source for an LPTMR peripheral to manage
the system timer, and the fast internal reference clock (FIRC) to generate a
48MHz core clock.

Serial Port
===========

The USB connector at the top left of the board (near the RESET button) is
connected to an OpenSDA chip which provides a serial USB device. This is
connected to the LPUART0 peripheral which the RI5CY and ZERO-RISCY cores use by
default for console and logging.

.. warning::

   The OpenSDA chip cannot be used to flash or debug the RISC-V cores.

   See the next section for flash and debug instructions for the
   RISC-V cores using an external JTAG dongle.

Programming and Debugging
*************************

.. _rv32m1-programming-hw:

.. important::

   To use this board, you will need:

   - a `SEGGER J-Link`_ debug probe to debug the RISC-V cores
   - a J-Link `9-Pin Cortex-M Adapter`_ board and ribbon cable
   - the SEGGER `J-Link Software and Documentation Pack`_ software
     installed

   A JTAG dongle is not included with the board itself.

Follow these steps to:

#. Get a toolchain and OpenOCD
#. Set up the board for booting RI5CY
#. Compile a Zephyr application for the RI5CY core
#. Flash the application to your board
#. Debug the board using GDB

.. _rv32m1-toolchain-openocd:

Get the Toolchain and OpenOCD
=============================

Before programming and debugging, you first need to get a GNU
toolchain and an OpenOCD build. There are vendor-specific versions of
each for the RV32M1 SoC\ [#toolchain_openocd]_.

Option 1 (Recommended): Prebuilt Toolchain and OpenOCD
------------------------------------------------------

The following prebuilt toolchains and OpenOCD archives are available
on the `OpenISA GitHub releases`_ page:

- :file:`Toolchain_Linux.tar.gz`
- :file:`Toolchain_Mac.tar.gz`
- :file:`Toolchain_Windows.zip`

Download and extract the archive for your system, then extract the
toolchain and OpenOCD archives inside.

Linux::

  tar xvzf Toolchain_Linux.tar.gz
  tar xvzf openocd.tar.gz
  tar xvzf riscv32-unknown-elf-gcc.tar.gz
  mv openocd ~/rv32m1-openocd
  mv riscv32-unknown-elf-gcc ~

macOS (unfortunately, the OpenISA 1.0.0 release's Mac
:file:`riscv32-unknown-elf-gcc.tar.gz` file doesn't expand into a
:file:`riscv32-unknown-elf-gcc` directory, so it has to be created)::

  tar xvzf Toolchain_Mac.tar.gz
  tar xvzf openocd.tar.gz
  mkdir riscv32-unknown-elf-gcc
  mv riscv32-unknown-elf-gcc.tar.gz riscv32-unknown-elf-gcc
  cd riscv32-unknown-elf-gcc/
  tar xvzf riscv32-unknown-elf-gcc.tar.gz
  cd ..
  mv openocd ~/rv32m1-openocd
  mv riscv32-unknown-elf-gcc ~

Windows:

#. Extract :file:`Toolchain_Windows.zip` in the file manager
#. Extract the :file:`openocd.zip` and :file:`riscv32-unknown-elf-gcc.zip` files
   in the resulting :file:`Toolchain_Windows` folder
#. Move the extracted :file:`openocd` folder to :file:`C:\\rv32m1-openocd`
#. Move the extracted :file:`riscv32-unknown-elf-gcc` folder to
   :file:`C:\\riscv32-unknown-elf-gcc`

For simplicity, this guide assumes:

- You put the extracted toolchain at :file:`~/riscv32-unknown-elf-gcc`
  on macOS or Linux, and :file:`C:\\riscv32-unknown-elf-gcc` on
  Windows.
- You put the extracted OpenOCD binary at :file:`~/rv32m1-openocd` on
  macOS or Linux, and the OpenOCD folder into :file:`C:\\rv32m1-openocd`
  on Windows.

You can put them elsewhere, but be aware:

- If you put the toolchain somewhere else, you will need to change
  the ``CROSS_COMPILE`` value described below accordingly.
- If you put OpenOCD somewhere else, you will need to change the
  OpenOCD path in the flashing and debugging instructions below.
- Don't use installation directories with spaces anywhere in the path;
  this won't work with Zephyr's build system.

Option 2: Building Toolchain and OpenOCD From Source
----------------------------------------------------

See :ref:`rv32m1_vega_toolchain_build`.

.. _rv32m1-vega-jtag:

JTAG Setup
==========

This section describes how to connect to your board via the J-Link
debugger and adapter board. See the :ref:`above information
<rv32m1-programming-hw>` for details on required hardware.

#. Connect the J-Link debugger through the adapter board to the
   VEGAboard as shown in the figure.

   .. figure:: rv32m1_vega_jtag.jpg
      :align: center
      :alt: RV32M1-VEGA

      VEGAboard connected properly to J-Link debugger.
      VEGAboard connector J55 should be used. Pin 1 is on the bottom left.

#. Power the VEGAboard via USB. The OpenSDA connector at the top left
   is recommended for UART access.

#. Make sure your J-Link is connected to your computer via USB.

One-Time Board Setup For Booting RI5CY or ZERO-RISCY
====================================================

Next, you'll need to make sure your board boots the RI5CY or ZERO-RISCY core.
**You only need to do this once.**

The RV32M1 SoC on the VEGAboard has multiple cores, any of which can
be selected as the boot core. Before flashing and debugging, you'll
first make sure you're booting the right core.

**Linux and macOS**:

.. note::

   Linux users: to run these commands as a normal user, you will need
   to install the `60-openocd.rules`_ udev rules file (usually by
   placing it in :file:`/etc/udev/rules.d`, then unplugging and
   plugging the J-Link in again via USB).

.. note::

   These Zephyr-specific instructions differ slightly from the
   equivalent SDK ones. The Zephyr OpenOCD configuration file does not
   run ``init``, so you have to do it yourself as explained below.

1. In one terminal, use OpenOCD to connect to the board::

     ~/rv32m1-openocd -f boards/openisa/rv32m1_vega/support/openocd_rv32m1_vega_ri5cy.cfg

   The output should look like this:

   .. code-block:: console

      $ ~/rv32m1-openocd -f boards/openisa/rv32m1_vega/support/openocd_rv32m1_vega_ri5cy.cfg
      Open On-Chip Debugger 0.10.0+dev-00431-ge1ec3c7d (2018-10-31-07:29)
      [...]
      Info : Listening on port 3333 for gdb connections
      Info : Listening on port 6666 for tcl connections
      Info : Listening on port 4444 for telnet connections

2. In another terminal, connect to OpenOCD's telnet server and execute
   the ``init`` and ``ri5cy_boot`` commands **with the reset button on
   the board (at top left) pressed down**::

     $ telnet localhost 4444
     Trying 127.0.0.1...
     Connected to localhost.
     Escape character is '^]'.
     Open On-Chip Debugger
     > init
     > ri5cy_boot

  To boot the ZERO-RISCY core instead, replace ``ri5cy_boot`` above with
  ``zero_boot``.

  The reset button is at top left, as shown in the following figure.

  .. figure:: ri5cy_boot.jpg
     :align: center
     :alt: Reset button is pressed

  Now quit the telnet session in this terminal and exit OpenOCD in the
  other terminal.

3. Unplug your J-Link and VEGAboard, and plug them back in.

**Windows**:

In one cmd.exe prompt in the Zephyr directory::

 C:\rv32m1-openocd\bin\openocd.exe rv32m1-openocd -f boards\openisa\rv32m1_vega\support\openocd_rv32m1_vega_ri5cy.cfg

In a telnet program of your choice:

#. Connect to localhost port 4444 using telnet.
#. Run ``init`` and ``ri5cy_boot`` as shown above, with RESET held down.
#. Quit the OpenOCD and telnet sessions.
#. Unplug your J-Link and VEGAboard, and plug them back in.

  To boot the ZERO-RISCY core instead, replace ``ri5cy_boot`` above with
  ``zero_boot``.

Compiling a Program
===================

.. important::

   These instructions assume you've set up a development system,
   cloned the Zephyr repository, and installed Python dependencies as
   described in the :ref:`getting_started`.

   You should also have already downloaded and installed the toolchain
   and OpenOCD as described above in :ref:`rv32m1-toolchain-openocd`.

The first step is to set up environment variables to point at your
toolchain and OpenOCD::

  # Linux or macOS
  export ZEPHYR_TOOLCHAIN_VARIANT=cross-compile
  export CROSS_COMPILE=~/riscv32-unknown-elf-gcc/bin/riscv32-unknown-elf-

  # Windows
  set ZEPHYR_TOOLCHAIN_VARIANT=cross-compile
  set CROSS_COMPILE=C:\riscv32-unknown-elf-gcc\bin\riscv32-unknown-elf-

.. note::

   The above only sets these variables for your current shell session.
   You need to make sure this happens every time you use this board.

Now let's compile the :zephyr:code-sample:`hello_world` application. (You can try
others as well; see :zephyr:code-sample-category:`samples` for more.)

.. We can't use zephyr-app-commands to provide build instructions
   due to the below mentioned linker issue.

Due to a toolchain `linker issue`_, you need to add an option setting
``CMAKE_REQUIRED_FLAGS`` when running CMake to generate a build system
(see :ref:`application` for information about Zephyr's build system).

Linux and macOS (run this in a terminal from the Zephyr directory)::

  # Set up environment and create build directory:
  source zephyr-env.sh

.. zephyr-app-commands::
   :zephyr-app: samples/hello_world
   :tool: cmake
   :cd-into:
   :board: rv32m1_vega/openisa_rv32m1/ri5cy
   :gen-args: -DCMAKE_REQUIRED_FLAGS=-Wl,-dT=/dev/null
   :goals: build

Windows (run this in a ``cmd`` prompt, from the Zephyr directory)::

  # Set up environment and create build directory
  zephyr-env.cmd
  cd samples\hello_world
  mkdir build & cd build

  # Use CMake to generate a Ninja-based build system:
  type NUL > empty.ld
  cmake -GNinja -DBOARD=rv32m1_vega/openisa_rv32m1/ri5cy -DCMAKE_REQUIRED_FLAGS=-Wl,-dT=%cd%\empty.ld ..

  # Build the sample
  ninja

Flashing
========

.. note::

   Make sure you've done the :ref:`JTAG setup <rv32m1-vega-jtag>`, and
   that the VEGAboard's top left USB connector is connected to your
   computer too (for UART access).

.. note::

   Linux users: to run these commands as a normal user, you will need
   to install the `60-openocd.rules`_ udev rules file (usually by
   placing it in :file:`/etc/udev/rules.d`, then unplugging and
   plugging the J-Link in again via USB).

Make sure you've followed the above instructions to set up your board
and build a program first.

Since you need to use a special OpenOCD, the easiest way to flash is
by using :ref:`west flash <west-build-flash-debug>` instead of ``ninja
flash`` like you might see with other Zephyr documentation.

Run these commands from the build directory where you ran ``ninja`` in
the above section.

Linux and macOS::

  # Don't use "~/rv32m1-openocd". It won't work.
  west flash --openocd=$HOME/rv32m1-openocd

Windows::

  west flash --openocd=C:\rv32m1-openocd\bin\openocd.exe

If you have problems:

- Make sure you don't have another ``openocd`` process running in the
  background.
- Unplug the boards and plug them back in.
- On Linux, make sure udev rules are installed, as described above.

As an alternative, for manual steps to run OpenOCD and GDB to flash,
see the `SDK README`_.

Debugging
=========

.. note::

   Make sure you've done the :ref:`JTAG setup <rv32m1-vega-jtag>`, and
   that the VEGAboard's top left USB connector is connected to your
   computer too (for UART access).

.. note::

   Linux users: to run these commands as a normal user, you will need
   to install the `60-openocd.rules`_ udev rules file (usually by
   placing it in :file:`/etc/udev/rules.d`, then unplugging and
   plugging the J-Link in again via USB).

Make sure you've followed the above instructions to set up your board
and build a program first.

To debug with gdb::

  # Linux, macOS
  west debug --openocd=$HOME/rv32m1-openocd

  # Windows
  west debug --openocd=C:\rv32m1-openocd\bin\openocd.exe

Then, from the ``(gdb)`` prompt, follow these steps to halt the core,
load the binary (:file:`zephyr.elf`), and re-sync with the OpenOCD
server::

  (gdb) monitor init
  (gdb) monitor reset halt
  (gdb) load
  (gdb) monitor gdb_sync
  (gdb) stepi

You can then set breakpoints and debug using normal GDB commands.

.. note::

   GDB can get out of sync with the target if you execute commands
   that reset it. To reset RI5CY and get GDB back in sync with it
   without reloading the binary::

     (gdb) monitor reset halt
     (gdb) monitor gdb_sync
     (gdb) stepi

If you have problems:

- Make sure you don't have another ``openocd`` process running in the
  background.
- Unplug the boards and plug them back in.
- On Linux, make sure udev rules are installed, as described above.

References
**********

- OpenISA developer portal: http://open-isa.org
- `OpenISA GitHub releases`_: includes toolchain and OpenOCD
  prebuilts, as well as documentation, such as the SoC datasheet and
  reference manual, board schematic and user guides, etc.
- Base toolchain: `pulp-riscv-gnu-toolchain`_; extra toolchain patches:
  `rv32m1_gnu_toolchain_patch`_ (only needed if building from source).
- OpenOCD repository: `rv32m1-openocd`_ (only needed if building from
  source).
- Vendor SDK: `rv32m1_sdk_riscv`_. Contains HALs, non-Zephyr sample
  applications, and information on using the board with Eclipse which
  may be interesting when combined with the Eclipse Debugging
  information in the :ref:`application`.

.. _rv32m1_vega_toolchain_build:

Appendix: Building Toolchain and OpenOCD from Source
****************************************************

.. note::

   Toolchain and OpenOCD build instructions are provided for Linux and
   macOS only.

   Instructions for building OpenOCD have only been verified on Linux.

.. warning::

   Don't use installation directories with spaces anywhere in
   the path; this won't work with Zephyr's build system.

Ubuntu 18.04 users need to install these additional dependencies::

  sudo apt-get install autoconf automake autotools-dev curl libmpc-dev \
                       libmpfr-dev libgmp-dev gawk build-essential bison \
                       flex texinfo gperf libtool patchutils bc zlib1g-dev \
                       libusb-1.0-0-dev libudev1 libudev-dev g++

Users of other Linux distributions need to install the above packages
with their system package manager.

macOS users need to install dependencies with Homebrew::

  brew install gawk gnu-sed gmp mpfr libmpc isl zlib

The build toolchain is based on the `pulp-riscv-gnu-toolchain`_, with
some additional patches hosted in a separate repository,
`rv32m1_gnu_toolchain_patch`_. To build the toolchain, follow the
instructions in the ``rv32m1_gnu_toolchain_patch`` repository's
`readme.md`_ file to apply the patches, then run::

  ./configure --prefix=<toolchain-installation-dir> --with-arch=rv32imc --with-cmodel=medlow --enable-multilib
  make

If you set ``<toolchain-installation-dir>`` to
:file:`~/riscv32-unknown-elf-gcc`, you can use the above instructions
for setting ``CROSS_COMPILE`` when building Zephyr
applications. If you set it to something else, you will need to update
your ``CROSS_COMPILE`` setting accordingly.

.. note::

   Strangely, there is no separate ``make install`` step for the
   toolchain. That is, the ``make`` invocation both builds and
   installs the toolchain. This means ``make`` has to be run as root
   if you want to set ``--prefix`` to a system directory such as
   :file:`/usr/local` or :file:`/opt` on Linux.

To build OpenOCD, clone the `rv32m1-openocd`_ repository, then run
these from the repository top level::

  ./bootstrap
  ./configure --prefix=<openocd-installation-dir>
  make
  make install

If ``<openocd-installation-dir>`` is :file:`~/rv32m1-openocd`, you
should set your OpenOCD path to :file:`~/rv32m1-openocd/bin/openocd`
in the above flash and debug instructions.

.. _RI5CY:
   https://github.com/pulp-platform/riscv
.. _ZERO-RISCY:
   https://github.com/pulp-platform/zero-riscy
.. _PULP platform:
   http://iis-projects.ee.ethz.ch/index.php/PULP

.. _pulp-riscv-gnu-toolchain:
   https://github.com/pulp-platform/pulp-riscv-gnu-toolchain
.. _rv32m1_gnu_toolchain_patch:
   https://github.com/open-isa-rv32m1/rv32m1_gnu_toolchain_patch
.. _rv32m1-openocd:
   https://github.com/open-isa-rv32m1/rv32m1-openocd
.. _readme.md:
   https://github.com/open-isa-rv32m1/rv32m1_gnu_toolchain_patch/blob/master/readme.md
.. _OpenISA GitHub releases:
   https://github.com/open-isa-org/open-isa.org/releases
.. _rv32m1_sdk_riscv:
   https://github.com/open-isa-rv32m1/rv32m1_sdk_riscv
.. _linker issue:
   https://github.com/pulp-platform/pulpino/issues/240
.. _60-openocd.rules:
   https://github.com/open-isa-rv32m1/rv32m1-openocd/blob/master/contrib/60-openocd.rules
.. _SEGGER J-Link:
   https://www.segger.com/products/debug-probes/j-link/
.. _9-Pin Cortex-M Adapter:
   https://www.segger.com/products/debug-probes/j-link/accessories/adapters/9-pin-cortex-m-adapter/
.. _J-Link Software and Documentation Pack:
   https://www.segger.com/downloads/jlink/#J-LinkSoftwareAndDocumentationPack
.. _SDK README:
   https://github.com/open-isa-rv32m1/rv32m1_sdk_riscv/blob/master/readme.md

.. rubric:: Footnotes

.. [#toolchain_openocd]

   For Linux users, the RISC-V toolchain in the :ref:`Zephyr SDK
   <toolchain_zephyr_sdk>` may work, but it hasn't been thoroughly tested with this
   SoC, and will not allow use of any available RISC-V ISA extensions.

   Support for the RV32M1 SoC is not currently available in the OpenOCD
   upstream repository or the OpenOCD build in the Zephyr SDK.