fix: M5Stack Unit C6L crash loop on boot

variants/m5stack_unit_c6l/UnitC6LBoard.h

@@ -1,12 +1,96 @@
 #pragma once
 
 #include <Arduino.h>
+#include <Wire.h>
 #include <helpers/ESP32Board.h>
 
+#define PI4IO_ADDR 0x43
+
+// PI4IO registers
+#define PI4IO_REG_CHIP_RESET 0x01
+#define PI4IO_REG_IO_DIR 0x03
+#define PI4IO_REG_OUT_SET 0x05
+#define PI4IO_REG_OUT_H_IM 0x07
+#define PI4IO_REG_IN_DEF_STA 0x09
+#define PI4IO_REG_PULL_EN 0x0B
+#define PI4IO_REG_PULL_SEL 0x0D
+#define PI4IO_REG_IRQ_STA 0x13
+#define PI4IO_REG_INT_MASK 0x11
+
 class UnitC6LBoard : public ESP32Board {
+private:
+  bool i2c_write_byte(uint8_t addr, uint8_t reg, uint8_t value) {
+    Wire.beginTransmission(addr);
+    Wire.write(reg);
+    Wire.write(value);
+    return Wire.endTransmission() == 0;
+  }
+
+  bool i2c_read_byte(uint8_t addr, uint8_t reg, uint8_t *value) {
+    Wire.beginTransmission(addr);
+    Wire.write(reg);
+    if (Wire.endTransmission() != 0) return false;
+    if (Wire.requestFrom(addr, (uint8_t)1) != 1) return false;
+    if (!Wire.available()) return false;
+    *value = Wire.read();
+    return true;
+  }
+
+  // P0=button, P1=unused input, P5=LNA_EN, P6=ANT_SW, P7=NRST(LoRa reset)
+  void resetLoRaViaPI4IO() {
+    uint8_t in_data;
+
+    // Reset the I/O expander to a known state
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_CHIP_RESET, 0xFF);
+    delay(10);
+    i2c_read_byte(PI4IO_ADDR, PI4IO_REG_CHIP_RESET, &in_data);
+    delay(10);
+
+    // Set P5, P6, P7 as outputs (0: input, 1: output)
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_IO_DIR, 0b11100000);
+    delay(10);
+
+    // Disable output high-impedance (i.e. enable the output driver) for
+    // every pin actually wired on this board: P0, P1, P5, P6, P7.
+    // Without this, IO_DIR + OUT_SET have no effect on the physical pin —
+    // it stays in the power-on Hi-Z state, so NRST never actually toggles.
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_OUT_H_IM, 0b00011100);
+    delay(10);
+
+    // Pull up/down select (0: down, 1: up)
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_PULL_SEL, 0b11100011);
+    delay(10);
+
+    // Pull up/down enable (0: disable, 1: enable)
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_PULL_EN, 0b11100011);
+    delay(10);
+
+    // Default input state for P0, P1 (buttons)
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_IN_DEF_STA, 0b00000011);
+    delay(10);
+
+    // Enable interrupts for P0, P1 (0: enable, 1: disable)
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_INT_MASK, 0b11111100);
+    delay(10);
+
+    // Set P7 (NRST) high, P5/P6 will be set after
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_OUT_SET, 0b10000000);
+    delay(10);
+
+    // Clear IRQ status
+    i2c_read_byte(PI4IO_ADDR, PI4IO_REG_IRQ_STA, &in_data);
+
+    // Enable RF switch (P6 high) and LNA (P5 high)
+    i2c_read_byte(PI4IO_ADDR, PI4IO_REG_OUT_SET, &in_data);
+    in_data |= (1 << 6);  // P6 = RF Switch = HIGH
+    in_data |= (1 << 5);  // P5 = LNA Enable = HIGH
+    i2c_write_byte(PI4IO_ADDR, PI4IO_REG_OUT_SET, in_data);
+  }
+
 public:
   void begin() {
-    ESP32Board::begin();
+    ESP32Board::begin();  // already calls Wire.begin(PIN_BOARD_SDA, PIN_BOARD_SCL)
+    resetLoRaViaPI4IO();
   }
 
   const char* getManufacturerName() const override {

variants/m5stack_unit_c6l/platformio.ini

@@ -6,7 +6,7 @@ build_flags =
   ${esp32c6_base.build_flags}
   ${sensor_base.build_flags}
   -I variants/m5stack_unit_c6l
-  -D P_LORA_TX_LED=15
+;  -D P_LORA_TX_LED=15
   -D P_LORA_SCLK=20
   -D P_LORA_MISO=22
   -D P_LORA_MOSI=21
@@ -15,11 +15,11 @@ build_flags =
   -D P_LORA_BUSY=19
   -D P_LORA_RESET=-1
   -D PIN_BUZZER=11
-  -D PIN_BOARD_SDA=16
-  -D PIN_BOARD_SCL=17
+  -D PIN_BOARD_SDA=10
+  -D PIN_BOARD_SCL=8
   -D SX126X_RXEN=5
   -D SX126X_DIO2_AS_RF_SWITCH=true
-  -D SX126X_DIO3_TCXO_VOLTAGE=1.8
+  -D SX126X_DIO3_TCXO_VOLTAGE=3.0
   -D SX126X_CURRENT_LIMIT=140
   -D SX126X_RX_BOOSTED_GAIN=1
   -D USE_SX1262