Fix SetStatusDelimiter: stack over-read and pointer-sign warnings

Two remaining issues in YEEP144_BluetoothUART.c, neither addressed by 1.2.

SetStatusDelimiter() transmits sizeof(rxBuf) = 10 bytes from an 8-byte stack
buffer (rxBuf is a different buffer declared earlier in the same function), so
two bytes of stack garbage follow every "SO" command the module receives. Send
strlen(txBuf) instead.

The same function passes char* to HAL_UART_Transmit(), which takes
const uint8_t*, producing three -Wpointer-sign warnings. They sit on the same
lines as the over-read, which is part of why it went unnoticed; with the casts
the file compiles warning-free.

See CODE_FIXES.md for the full write-up.

CODE_FIXES.md

@@ -0,0 +1,108 @@
+# CODE_FIXES — YEEP-144 library
+
+Two fixes to `YEEP144lib/src/YEEP144_BluetoothUART.c`, against the **1.2 release**.
+
+Both are pre-existing issues that 1.2 does not address.
+
+> **Already fixed in 1.2, not part of this change:** an earlier report covered
+> `YEEP144_BluetoothUART_Init()` entering the RN4678's command mode and
+> rebooting the module on every boot (by calling `SetStatusDelimiter()`
+> unconditionally). 1.2 has removed that call from `Init()`, so no change is
+> needed here. See "Suggested follow-up" below.
+
+| # | Fix | Severity |
+|---|---|---|
+| 1 | `SetStatusDelimiter()` over-reads a stack buffer | Medium — undefined behaviour, and it sends garbage to the module |
+| 2 | Three `-Wpointer-sign` warnings in the same function | Low — but they sit on the same lines as #1 |
+
+---
+
+## Fix 1 — SetStatusDelimiter over-reads a stack buffer
+
+### Root cause
+
+```c
+uint8_t rxBuf[10];
+...
+char txBuf[8] = {0};
+if(prefix == '\0' && postfix == '\0'){
+    sprintf(txBuf, "SO,,%c",'\r');
+}
+...
+HAL_UART_Transmit(&huart2, txBuf, sizeof(rxBuf), UART_POLL_TIMEOUT);
+                                    ^^^^^^^^^^^^ rxBuf is uint8_t[10]
+```
+
+`rxBuf` is a **different, unrelated** buffer declared earlier in the same
+function. This transmits **10 bytes from an 8-byte array** — a two-byte stack
+over-read, so two bytes of stack garbage follow every `SO` command the module
+receives.
+
+1.2 no longer calls this function from `Init()`, so it is only reachable if an
+application calls `YEEP144_BluetoothUART_SetStatusDelimiter()` directly. It is
+still a public API function, and the over-read is undefined behaviour either way.
+
+### Patch
+
+```c
+HAL_UART_Transmit(&huart2, (const uint8_t *)txBuf, (uint16_t)strlen(txBuf),
+                  UART_POLL_TIMEOUT);
+```
+
+`strlen()` is the right length: it stops at the terminating NUL that
+`sprintf()` wrote. `sizeof(txBuf)` would also fix the over-read, but would
+still transmit the padding NULs that `sprintf()` left in the buffer.
+
+---
+
+## Fix 2 — Three pointer-sign warnings
+
+### Symptom
+
+```
+warning: pointer targets in passing argument 2 of 'HAL_UART_Transmit' differ in
+         signedness [-Wpointer-sign]
+```
+
+at three call sites in `SetStatusDelimiter()`.
+
+### Root cause
+
+`HAL_UART_Transmit()` takes `const uint8_t *`; the function passes `char *`
+(two string literals, and `txBuf`).
+
+### Patch
+
+Cast at the three call sites:
+
+```c
+HAL_UART_Transmit(&huart2, (const uint8_t *)"$$$", 3, UART_POLL_TIMEOUT);
+HAL_UART_Transmit(&huart2, (const uint8_t *)txBuf, (uint16_t)strlen(txBuf), UART_POLL_TIMEOUT);
+HAL_UART_Transmit(&huart2, (const uint8_t *)"R,1", 3, UART_POLL_TIMEOUT);
+```
+
+With this, the file compiles warning-free.
+
+---
+
+## Suggested follow-up (not part of this change)
+
+1.2 removed the module configuration from `Init()`. The capability itself is
+still worth having, as an explicitly-named function rather than a side effect of
+startup — e.g. `YEEP144_BluetoothUART_ConfigureModule()`, documented as taking
+several seconds, entering the module's command mode, rebooting the module, and
+therefore dropping any active connection.
+
+---
+
+## Files changed
+
+| File | Change |
+|---|---|
+| `YEEP144lib/src/YEEP144_BluetoothUART.c` | Both fixes — 7 insertions, 3 deletions against `main` |
+
+## Repository note
+
+`Drivers/` (the vendored ST HAL and CMSIS) is not in this repository: it is
+173 MB, of which 108 MB is ST's `.chm` user manuals. Fetch it from
+STMicroelectronics/STM32CubeH5 if you need to build.

YEEP144lib/src/YEEP144_BluetoothUART.c

@@ -192,7 +192,7 @@ void YEEP144_BluetoothUART_SetStatusDelimiter(char prefix, char postfix){
     uint16_t rxSize;
 
     // Enter command mode
-    HAL_UART_Transmit(&huart2, "$$$", 3, UART_POLL_TIMEOUT);
+    HAL_UART_Transmit(&huart2, (const uint8_t *)"$$$", 3, UART_POLL_TIMEOUT);
 
     // Wait to receive data back from BT module
     HAL_UARTEx_ReceiveToIdle(&huart2, rxBuf, 10, &rxSize, UART_POLL_TIMEOUT);
@@ -211,13 +211,17 @@ void YEEP144_BluetoothUART_SetStatusDelimiter(char prefix, char postfix){
     else{
         sprintf(txBuf, "SO,%c,%c%c", prefix, postfix, '\r');
     }
-    HAL_UART_Transmit(&huart2, txBuf, sizeof(rxBuf), UART_POLL_TIMEOUT);
+    // rxBuf is a different, unrelated buffer (uint8_t rxBuf[10]); using its
+    // size here transmits 10 bytes from this 8-byte array, so two bytes of
+    // stack garbage follow every command. Send exactly the string.
+    HAL_UART_Transmit(&huart2, (const uint8_t *)txBuf, (uint16_t)strlen(txBuf),
+                      UART_POLL_TIMEOUT);
 
     // Wait to receive data back from BT module
     HAL_UARTEx_ReceiveToIdle(&huart2, rxBuf, 10, &rxSize, UART_POLL_TIMEOUT);
     
     // Reboot device to make changes
-    HAL_UART_Transmit(&huart2, "R,1", 3, UART_POLL_TIMEOUT);
+    HAL_UART_Transmit(&huart2, (const uint8_t *)"R,1", 3, UART_POLL_TIMEOUT);
 
     // Wait to receive data back from BT module
     HAL_UARTEx_ReceiveToIdle(&huart2, rxBuf, 10, &rxSize, UART_POLL_TIMEOUT);