Add ESP-IDF and STM32 C examples; document platform examples

Both compile the same portable core (src/meshcore_companion.c) and differ only in the UART transport: - examples-esp-idf/tty_bridge: full ESP-IDF project (UART driver), core compiled directly via the component CMakeLists (no copy) - examples-stm32/uart_bridge: HAL drop-in (meshcore_setup/meshcore_poll) for a CubeMX/CubeIDE project, with integration README README updated: new examples in layout + an 'Other platform examples' section. Verified host build/test still pass and both new examples pass -Wall -Wextra syntax checks against stubbed platform headers. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-06-08 02:21:22 +10:00
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+# STM32 example: uart_bridge
+
+Integration example showing how to drive a MeshCore Companion Radio from an STM32
+using the CubeMX-generated HAL. The protocol logic is the repo's portable C core
+(`src/meshcore_companion.c`); this file supplies only the UART transport and two
+entry points you call from your generated `main()`.
+
+Because an STM32 firmware build is tied to your specific MCU, clocks, pins and
+linker script (all produced by STM32CubeIDE / CubeMX), this is **not** a
+standalone buildable project — it is a drop-in.
+
+## Steps (STM32CubeIDE / CubeMX)
+
+1. Generate a project with one USART enabled at **115200 8N1** (e.g. `USART1`).
+   Wire it to the companion radio: host TX → radio RX, host RX ← radio TX, GND↔GND.
+   The radio must run the serial companion firmware (`companion_radio_usb`).
+2. Add `src/meshcore_companion.c` and `src/meshcore_companion.h` from this repo to
+   your project (or add this repo's `src/` to the include paths).
+3. Add `meshcore_stm32.c` to your project. If your USART handle isn't `huart1`,
+   change the `extern UART_HandleTypeDef huart1;` line near the top.
+4. In the generated `main.c`:
+   ```c
+   /* USER CODE BEGIN 2 */
+   meshcore_setup();
+   /* USER CODE END 2 */
+
+   while (1) {
+       /* USER CODE BEGIN 3 */
+       meshcore_poll();
+   }
+   ```
+
+## Notes
+
+- `meshcore_poll()` polls the UART one byte at a time, which is fine for the
+  companion's low data rate. For high throughput, switch the RX side to
+  interrupt/DMA into a ring buffer and feed that to `mc_rx_feed()` — the core
+  code is unchanged.
+- Logging uses `printf()`. Retarget it to a **separate** debug UART or SWO/ITM
+  (commonly USART2 = the ST-Link VCP) by implementing `_write()`; do not point it
+  at the companion UART.
+- The same two-function transport pattern (`send bytes` / `read available bytes`)
+  ports directly to bare-metal STM32, nRF52 (nRF5 SDK or Zephyr), or any other
+  MCU — only the HAL calls change.