message: Make UART block until transmission completes
diff: @@ -47,6 +47,9 @@ int _write(int file, char *data, int len) {
  // Start DMA background trasnfer
  HAL_UART_Transmit_DMA(&huart4, uart_tx_buf, len);
  } break;
  + while (huart4.gState != HAL_UART_STATE_READY) {
  + // Do nothing
  + }
  default: {
  written = 0;
  