feat(stm32wl): add reboot-to-bootloader support via enter_dfu_mode_request (#10158)

src/modules/AdminModule.cpp

@@ -480,7 +480,7 @@ bool AdminModule::handleReceivedProtobuf(const meshtastic_MeshPacket &mp, meshta
 #if HAS_SCREEN
         IF_SCREEN(screen->showSimpleBanner("Device is rebooting\ninto DFU mode.", 0));
 #endif
-#if defined(ARCH_NRF52) || defined(ARCH_RP2040)
+#if defined(ARCH_NRF52) || defined(ARCH_RP2040) || defined(ARCH_STM32WL)
         enterDfuMode();
 #endif
         break;

src/platform/stm32wl/main-stm32wl.cpp

@@ -4,6 +4,57 @@
 #include <stm32wle5xx.h>
 #include <stm32wlxx_hal.h>
 
+// ─── Bootloader redirect ──────────────────────────────────────────────────────
+//
+// Why .noinit + constructor instead of TAMP backup registers:
+//
+//   The STM32duino startup sequence initialises clocks which may call
+//   __HAL_RCC_BACKUPRESET_FORCE/RELEASE when configuring the LSE oscillator,
+//   wiping the entire backup domain (including TAMP->BKP0R) before setup()
+//   ever runs. The backup-register approach therefore cannot reliably survive
+//   a soft reset in this toolchain.
+//
+//   Solution: store the magic in a .noinit SRAM variable.
+//   - NVIC_SystemReset() does NOT clear SRAM.
+//   - The linker script skips zero-init for .noinit sections.
+//   - __attribute__((constructor)) fires before main()/HAL_Init(), so we can
+//     intercept and jump before anything disturbs peripheral state.
+
+#define BOOTLOADER_MAGIC 0xD00DB007UL
+#define SYS_MEM_BASE 0x1FFF0000UL
+
+// Placed in .noinit — not zeroed at startup, survives NVIC_SystemReset().
+__attribute__((section(".noinit"), used)) volatile uint32_t g_bootloaderMagic;
+
+// Fires before main() / HAL_Init(). Must use only core Cortex-M registers.
+__attribute__((constructor(101), used)) static void earlyBootCheck(void)
+{
+    if (g_bootloaderMagic != BOOTLOADER_MAGIC)
+        return;
+    g_bootloaderMagic = 0;
+
+    SysTick->CTRL = 0;
+    SysTick->LOAD = 0;
+    SysTick->VAL = 0;
+    for (int i = 0; i < 8; i++) {
+        NVIC->ICER[i] = 0xFFFFFFFF;
+        NVIC->ICPR[i] = 0xFFFFFFFF;
+    }
+    __DSB();
+    __ISB();
+    SCB->VTOR = SYS_MEM_BASE;
+    __set_MSP(*(volatile uint32_t *)SYS_MEM_BASE);
+    ((void (*)(void))(*(volatile uint32_t *)(SYS_MEM_BASE + 4)))();
+    while (1)
+        ;
+}
+
+void enterDfuMode()
+{
+    g_bootloaderMagic = BOOTLOADER_MAGIC;
+    HAL_NVIC_SystemReset();
+}
+
 void setBluetoothEnable(bool enable) {}
 
 void playStartMelody() {}