Implement _write function for printf

project/Core/Src/main.c

@@ -22,7 +22,8 @@
 
 /* Private includes ----------------------------------------------------------*/
 /* USER CODE BEGIN Includes */
-
+#include <errno.h>
+#include <sys/unistd.h>
 /* USER CODE END Includes */
 
 /* Private typedef -----------------------------------------------------------*/
@@ -430,7 +431,24 @@ static void MX_GPIO_Init(void)
 }
 
 /* USER CODE BEGIN 4 */
+int _write(int file, char *data, int len) {
+    HAL_StatusTypeDef status;
 
+    switch (file) {
+        case STDOUT_FILENO:
+        case STDERR_FILENO:
+            status = HAL_UART_Transmit(&huart1, (uint8_t*)data, len, HAL_MAX_DELAY);
+            if (status != HAL_OK) {
+                errno = EIO;
+                return -1;
+            }
+            break;
+        default:
+            errno = EBADF;
+            return -1;
+    }
+    return len;
+}
 /* USER CODE END 4 */
 
 /**