[UART] Add private function to get serial_t obj

Signed-off-by: Frederic.Pillon <[email protected]>

Author: fpistm

cores/arduino/stm32/uart.c

@@ -104,6 +104,19 @@ static serial_t *tx_callback_obj[UART_NUM];
 
 static serial_t serial_debug = { .uart = NP, .index = UART_NUM };
 
+/* Aim of the function is to get serial_s pointer using huart pointer */
+/* Highly inspired from magical linux kernel's "container_of" */
+serial_t *get_serial_obj(UART_HandleTypeDef *huart)
+{
+  struct serial_s *obj_s;
+  serial_t *obj;
+
+  obj_s = (struct serial_s *)((char *)huart - offsetof(struct serial_s, handle));
+  obj = (serial_t *)((char *)obj_s - offsetof(serial_t, uart));
+
+  return (obj);
+}
+
 /**
   * @brief  Function called to initialize the uart interface
   * @param  obj : pointer to serial_t structure

cores/arduino/stm32/uart.h

@@ -53,6 +53,11 @@ extern "C" {
 typedef struct serial_s serial_t;
 
 struct serial_s {
+  /*  The 1st 2 members USART_TypeDef *uart
+   *  and UART_HandleTypeDef handle should
+   *  be kept as the first members of this struct
+   *  to have get_serial_obj() function work as expected
+   */
   USART_TypeDef *uart;
   UART_HandleTypeDef handle;
   uint32_t baudrate;