feat: Allow fw to reboot-to-bootloader when special sequence is sent to I2C, addr 0x39

Author: tuxuser

firmware/userapp/Core/Inc/slave.h

@@ -9,6 +9,15 @@ extern "C" {
 
 #define REG_MAP_SIZE      0x25
 
+// I2C1 main slave address (unshifted)
+#define MAX6958_SLAVE_I2C_ADDR 0x38
+// Secondary I2C1 own-address (7-bit, unshifted): writing BOOTLOADER_TRIGGER_MAGIC
+// here reboots straight into the STM32 system bootloader (DFU), letting the
+// board be reflashed without physical button/SWD access.
+#define BOOTLOADER_TRIGGER_I2C_ADDR   0x39
+// Magic bytes, MSB first: 0xB0 0x07 0xB0 0x07 ("B007 B007" / "BOOT BOOT")
+#define BOOTLOADER_TRIGGER_MAGIC      0xB007B007UL
+
 void Slave_Init(void);
 
 uint8_t Slave_RegRead(uint8_t addr);

firmware/userapp/Core/Src/main.c

@@ -219,10 +219,10 @@ static void MX_I2C1_Init(void)
   /* USER CODE END I2C1_Init 1 */
   hi2c1.Instance = I2C1;
   hi2c1.Init.Timing = 0x00C12166;
-  hi2c1.Init.OwnAddress1 = 112;
+  hi2c1.Init.OwnAddress1 = (MAX6958_SLAVE_I2C_ADDR << 1);
   hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
-  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
-  hi2c1.Init.OwnAddress2 = 0;
+  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_ENABLE;
+  hi2c1.Init.OwnAddress2 = (BOOTLOADER_TRIGGER_I2C_ADDR << 1);
   hi2c1.Init.OwnAddress2Masks = I2C_OA2_NOMASK;
   hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
   hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_ENABLE;

firmware/userapp/Core/Src/slave.c

@@ -1,4 +1,5 @@
 #include "slave.h"
+#include "bootloader.h"
 
 extern I2C_HandleTypeDef hi2c1;
 
@@ -9,6 +10,9 @@ static uint8_t reg_index = 0;              // Current write address
 static uint32_t error = HAL_OK;
 static uint8_t error_state = 0;
 
+static uint8_t bootloader_magic_buf[4] = {0};
+static uint8_t receiving_boot_magic = 0;   // Set while a BOOTLOADER_TRIGGER_I2C_ADDR write is in flight
+
 void Slave_Start(void);
 
 /**
@@ -43,7 +47,17 @@ void HAL_I2C_AddrCallback(I2C_HandleTypeDef *hi2c, uint8_t TransferDirection, ui
         // Check if master->slave transmission
         if (TransferDirection == I2C_DIRECTION_TRANSMIT)
         {
-                HAL_StatusTypeDef ret = HAL_I2C_Slave_Seq_Receive_IT(&hi2c1, &reg_index, 1, I2C_NEXT_FRAME);
+                HAL_StatusTypeDef ret;
+
+                // AddrMatchCode is delivered pre-shifted by 1 (same convention as
+                // Init.OwnAddress1/OwnAddress2), not the raw 7-bit address.
+                if (AddrMatchCode == (BOOTLOADER_TRIGGER_I2C_ADDR << 1)) {
+                        receiving_boot_magic = 1;
+                        ret = HAL_I2C_Slave_Seq_Receive_IT(&hi2c1, bootloader_magic_buf, sizeof(bootloader_magic_buf), I2C_LAST_FRAME);
+                } else {
+                        ret = HAL_I2C_Slave_Seq_Receive_IT(&hi2c1, &reg_index, 1, I2C_NEXT_FRAME);
+                }
+
                 if (ret != HAL_OK) {
                         Error_Handler();
                 }
@@ -65,6 +79,20 @@ void HAL_I2C_SlaveRxCpltCallback(I2C_HandleTypeDef *hi2c)
                 return;
         }
 
+        if (receiving_boot_magic) {
+                receiving_boot_magic = 0;
+
+                uint32_t magic = ((uint32_t)bootloader_magic_buf[0] << 24)
+                                | ((uint32_t)bootloader_magic_buf[1] << 16)
+                                | ((uint32_t)bootloader_magic_buf[2] << 8)
+                                |  (uint32_t)bootloader_magic_buf[3];
+
+                if (magic == BOOTLOADER_TRIGGER_MAGIC) {
+                        resetToSystemBootLoader(); // Does not return
+                }
+                return;
+        }
+
         if (HAL_I2C_Slave_Seq_Receive_IT(hi2c, &register_map[reg_index++], 1, I2C_NEXT_FRAME) != HAL_OK) {
                 Error_Handler();
         }
@@ -105,9 +133,17 @@ void HAL_I2C_ErrorCallback(I2C_HandleTypeDef *hi2c)
                 default:
                         Error_Handler();
         }
-        
+                        
         hi2c->ErrorCode = 0;
-        Slave_HandleComplete();
+
+        if (receiving_boot_magic) {
+                // Truncated bootloader-trigger write; discard it rather than
+                // let stale reg_index state be mistaken for a completed
+                // register-map transfer below.
+                receiving_boot_magic = 0;
+        } else {
+                Slave_HandleComplete();
+        }
 
         Slave_Start();