feat: Improve Swan 3V3 pin control/behavior

- Define constant to reference `DISCHARGE_3V3` pin.
- Define constants `ENABLE_DISCHARGING` and `DISABLE_DISCHARGING` to manipulate `DISCHARGE_3V3` pin.
- Initialize `ENABLE_3V3` pin to be on, and `DISCHARGE_3V3` to be disabled.

variants/STM32L4xx/L4R5Z(G-I)Y_L4R9Z(G-I)Y_L4S5ZIY_L4S9ZIY/variant_SWAN_R5.cpp

@@ -118,6 +118,23 @@ const uint32_t analogInputPin[] = {
 extern "C" {
 #endif
 
+WEAK void initVariant(void)
+{
+  /* Initialize the 3V3 discharge to be OFF and the output power to be ON */
+  __HAL_RCC_GPIOE_CLK_ENABLE();
+  GPIO_InitTypeDef  GPIO_InitStruct;
+  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;
+  GPIO_InitStruct.Pull = GPIO_NOPULL;
+  GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
+  GPIO_InitStruct.Pin = GPIO_PIN_6;
+  HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);
+  HAL_GPIO_WritePin(GPIOE, GPIO_PIN_6, GPIO_PIN_SET);
+  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
+  GPIO_InitStruct.Pin = GPIO_PIN_4;
+  HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);
+  HAL_GPIO_WritePin(GPIOE, GPIO_PIN_4, GPIO_PIN_SET);
+}
+
 /**
   * @brief  System Clock Configuration
   * @param  None

variants/STM32L4xx/L4R5Z(G-I)Y_L4R9Z(G-I)Y_L4S5ZIY_L4S9ZIY/variant_SWAN_R5.h

@@ -181,10 +181,15 @@
   #define USER_BTN              PC13
 #endif
 
-// Power switch EN pin
+// Power switch ENABLE and DISCHARGE pins
 #ifndef ENABLE_3V3
   #define ENABLE_3V3            PE4
 #endif
+#ifndef DISCHARGE_3V3
+  #define DISCHARGE_3V3         PE6
+  #define DISABLE_DISCHARGING   HIGH
+  #define ENABLE_DISCHARGING    LOW
+#endif
 
 // SPI definitions
 #ifndef PIN_SPI_SS