autohuttli: add the CH32V003 I2C interceptor

.gitignore

@@ -3,3 +3,5 @@ secrets.yaml
 .esphome/
 dist/
 __pycache__/
+build/
+tmp.*

atoms3_lite.yaml

@@ -39,7 +39,7 @@ update:
   - platform: http_request
     id: auto_update
     source: "https://juju.nz/michaelh/assets/esphome/${project_name}.json"
-    update_interval: 2min
+    update_interval: 4hours
 
 interval:
   - interval: 50s

interceptor/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.13.1)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+
+project(app LANGUAGES CXX)
+
+target_sources(app PRIVATE src/main.cc)

interceptor/README.md

@@ -0,0 +1,8 @@
+# Interceptor
+
+A passive digital signal sampler for the CH32V003. Tracks the levels of PC1 and PC2 and sends any
+changes over serial to the host. These can be converted to a VCD format file and analyzed in
+sigrock.
+
+Designed for sniffing I2C traffic. PC1 and PC2 are 5 V tollerant and have pullups enabled. Tested at
+up to 200 kHz.

interceptor/boards/wch_ch32v003evt.overlay

@@ -0,0 +1,48 @@
+#include <zephyr/dt-bindings/pinctrl/ch32v003-pinctrl.h>
+
+/ {
+	chosen {
+		zephyr,console = &usart1;
+		zephyr,shell-uart = &usart1;
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		red_led: led0 {
+			gpios = <&gpioa 1 GPIO_ACTIVE_HIGH>;
+		};
+
+		scl_pin: scl_pin {
+			gpios = <&gpioc 2 GPIO_PULL_UP>;
+		};
+
+		sda_pin: sda_pin {
+			gpios = <&gpioc 1 GPIO_PULL_UP>;
+		};
+	};
+
+	aliases {
+		led0 = &red_led;
+		scl = &scl_pin;
+		sda = &sda_pin;
+	};
+};
+
+&pinctrl {
+};
+
+&gpioa {
+	status = "okay";
+};
+
+&gpioc {
+	status = "okay";
+};
+
+&usart1 {
+	status = "okay";
+	current-speed = <460800>;
+	pinctrl-0 = <&usart1_default>;
+	pinctrl-names = "default";
+};

interceptor/prj.conf

@@ -0,0 +1,25 @@
+# Trim back the memory usage.
+CONFIG_THREAD_STACK_INFO=n
+CONFIG_ERRNO=n
+CONFIG_CURRENT_THREAD_USE_TLS=n
+CONFIG_TIMESLICING=n
+CONFIG_KERNEL_MEM_POOL=n
+CONFIG_COMMON_LIBC_MALLOC=n
+CONFIG_MINIMAL_LIBC=y
+CONFIG_CBPRINTF_NANO=y
+CONFIG_CBPRINTF_REDUCED_INTEGRAL=y
+CONFIG_CBPRINTF_N_SPECIFIER=n
+
+CONFIG_WCH_CH32V00X_HSI=y
+CONFIG_WCH_CH32V00X_HSE=n
+CONFIG_WCH_CH32V00X_HSI_AS_PLLSRC=y
+
+CONFIG_GPIO=y
+CONFIG_SERIAL=y
+CONFIG_CONSOLE=y
+CONFIG_UART_CONSOLE=y
+
+CONFIG_CPP=y
+CONFIG_STD_CPP2B=y
+
+CONFIG_MAIN_STACK_SIZE=1024

interceptor/src/main.cc

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2024 Google LLC.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/drivers/gpio.h>
+#include <zephyr/kernel.h>
+
+#include <ch32_gpio.h>
+#include <ch32_uart.h>
+
+namespace
+{
+
+constexpr struct gpio_dt_spec kLed = GPIO_DT_SPEC_GET(DT_ALIAS(led0), gpios);
+constexpr struct gpio_dt_spec kScl = GPIO_DT_SPEC_GET(DT_ALIAS(scl), gpios);
+constexpr struct gpio_dt_spec kSda = GPIO_DT_SPEC_GET(DT_ALIAS(sda), gpios);
+
+void sniff()
+{
+	GPIO_TypeDef *port = GPIOC;
+	USART_TypeDef *uart = USART1;
+	uint8_t fifo[256];
+	int head = 0;
+	int tail = 0;
+
+	// Note that using `int` reduces the code size by removing unneeded truncation.
+	int samples = 0;
+	int sample_count = 0;
+	int last_sample = 0;
+	int unchanged_for = 0;
+
+	csr_clear(mstatus, MSTATUS_IEN);
+
+	for (;;) {
+		static_assert(kScl.port == kSda.port);
+		static_assert(kScl.pin == kSda.pin + 1);
+		int sample = (port->INDR >> kSda.pin) & 3;
+
+		// Record when the value changes, or the value has been unchanged for some time.
+		if (sample != last_sample || ++unchanged_for >= 1024) {
+			samples <<= 2;
+			samples |= sample;
+			last_sample = sample;
+			unchanged_for = 0;
+
+			if (++sample_count >= 3) {
+				// Encode the three samples into valid ASCII.
+				fifo[head++] = samples + ' ';
+				head %= sizeof(fifo);
+				samples = 0;
+				sample_count = 0;
+			}
+		}
+		if (tail != head && (uart->STATR & USART_STATR_TXE) != 0) {
+			uart->DATAR = fifo[tail++];
+			tail %= sizeof(fifo);
+
+			if (tail == 0 && (uart->STATR & USART_STATR_RXNE) != 0 &&
+			    uart->DATAR == '~') {
+				break;
+			}
+		}
+	}
+
+	csr_set(mstatus, MSTATUS_IEN);
+}
+
+void interceptor()
+{
+	gpio_pin_configure_dt(&kLed, GPIO_OUTPUT_ACTIVE);
+	gpio_pin_configure_dt(&kScl, GPIO_INPUT);
+	gpio_pin_configure_dt(&kSda, GPIO_INPUT);
+
+	for (;;) {
+		printk("sniff\n");
+		sniff();
+	}
+}
+
+} // namespace
+
+int main(void)
+{
+	interceptor();
+	return 0;
+}

interceptor/tovcd.py

@@ -0,0 +1,49 @@
+"""Converts the samples from the board to a VCD file for sigrok.
+
+Usage:
+   python3 tovcd.py < /dev/ttyUSB0 | tee log.vcd
+"""
+
+import datetime
+import sys
+
+_HEADER = """
+$date {date} $end
+$version juju.nz tovcd.py $end
+$timescale 1 us $end
+$scope module libsigrok $end
+"""
+
+_MID = """
+$upscope $end
+$enddefinitions $end
+"""
+
+_IDS = "!#$%&'()"
+
+
+def main():
+    print(_HEADER.strip().format(date=datetime.datetime.now()))
+
+    for wire in range(2):
+        print(f"$var wire 1 {_IDS[wire]} D{wire} $end")
+
+    print(_MID.strip())
+
+    now = 0
+    last_d = None
+
+    for ch in sys.stdin.read():
+        ch = ord(ch) - 32
+        for i in range(3):
+            now += 1
+            d = (ch >> 5) & 1, (ch >> 4) & 1
+            ch <<= 2
+            if d != last_d:
+                parts = (f"{x}{_IDS[i]}" for i, x in enumerate(d))
+                print(f"#{now}", " ".join(parts))
+                last_d = d
+
+
+if __name__ == "__main__":
+    main()