Как надо дружиться с STM32

int main(void) {
  HAL_Init();
  uart_init();
  while(1) {
    uart_loop();
  }
  return 1; // never
}

// from uart.c
void uart_init(void) {
  uart.Instance = USARTx;

  uart.Init.BaudRate = 57600;
  uart.Init.WordLength = UART_WORDLENGTH_8B;
  uart.Init.Parity = UART_PARITY_NONE;
  uart.Init.StopBits = UART_STOPBITS_1;
  uart.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  uart.Init.Mode = UART_MODE_TX_RX;

  if(HAL_UART_Init(&uart) != HAL_OK) {
    Error_Handler();
  }
}

void uart_loop(void) {

  if(HAL_UART_Receive(&uart, rx_buf + rx_buf_idx, 1, UART_TIMEOUT) != HAL_OK) {
    return;
  }
  rx_buf_idx++;

  LEDg_ON();
  HAL_Delay(10);
  LEDg_OFF();

  // buffer full
  if(rx_buf_idx == BUFSIZE) {
    _uart_flush();
  }

  if(rx_buf[rx_buf_idx - 1] == '\r' || rx_buf[rx_buf_idx - 1] == '\n') {
    _uart_flush();
  }
}

static void _uart_flush(void) {
  // wait for tx_buf
  while(!_uart_tx_ready);

  memcpy(tx_buf, rx_buf, rx_buf_idx);
  tx_buf_idx = rx_buf_idx;
  rx_buf_idx = 0;

  LEDo_ON();
  if(HAL_UART_Transmit_DMA(&uart, tx_buf, tx_buf_idx) != HAL_OK) {
    Error_Handler();
  }
}

// uart dma/it tx complete callback 
void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart) {
  _uart_tx_ready = 1;
  LEDo_OFF();
}

// uart dma/it error callback
void HAL_UART_ErrorCallback(UART_HandleTypeDef *huart) {
  LEDr_ON();
  // FIXME: irq prio
  HAL_Delay(50);
  LEDr_OFF();
  _uart_tx_ready = 1;
}

DMA_HandleTypeDef uart_tx_dma;

// HAL_UART_Init callback to init required periph
void HAL_UART_MspInit(UART_HandleTypeDef *huart) {
  USARTx_RX_CLK_EN();
  USARTx_TX_CLK_EN();
  USARTx_CLK_EN();
  USARTx_DMA_CLK_EN();

  GPIO_InitTypeDef gpio;

  gpio.Pin = USARTx_TX_PIN;
  gpio.Mode = GPIO_MODE_AF_PP;
  gpio.Speed = GPIO_SPEED_FAST;
  gpio.Pull = GPIO_NOPULL;
  gpio.Alternate = USARTx_TX_AF;
  HAL_GPIO_Init(USARTx_TX_PORT, &gpio);

  gpio.Pin = USARTx_RX_PIN;
  gpio.Alternate = USARTx_RX_AF;
  HAL_GPIO_Init(USARTx_RX_PORT, &gpio);

  // not used currently
//  HAL_NVIC_SetPriority(USARTx_IRQn, 0, 1);
//  HAL_NVIC_EnableIRQ(USARTx_IRQn);

  uart_tx_dma.Instance = USARTx_DMA_TX_STREAM;
  uart_tx_dma.Init.Channel = USARTx_DMA_TX_CHANNEL;
  uart_tx_dma.Init.Direction = DMA_MEMORY_TO_PERIPH;
  uart_tx_dma.Init.Mode = DMA_NORMAL;
  uart_tx_dma.Init.PeriphInc = DMA_PINC_DISABLE;
  uart_tx_dma.Init.MemInc = DMA_MINC_ENABLE;
  uart_tx_dma.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE;
  uart_tx_dma.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE;
  uart_tx_dma.Init.Priority = DMA_PRIORITY_LOW;
  uart_tx_dma.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
  uart_tx_dma.Init.FIFOThreshold = DMA_FIFO_THRESHOLD_FULL;
  uart_tx_dma.Init.MemBurst = DMA_MBURST_INC4;
  uart_tx_dma.Init.PeriphBurst = DMA_PBURST_INC4;

  HAL_DMA_Init(&uart_tx_dma);
  __HAL_LINKDMA(huart,hdmatx,uart_tx_dma);

  HAL_NVIC_SetPriority(USARTx_DMA_TX_IRQn, 0, 1);
  HAL_NVIC_EnableIRQ(USARTx_DMA_TX_IRQn);

  // indication leds rcc en
  LEDg_CLK_EN();
  LEDo_CLK_EN();

  // rx indication led
  gpio.Pin = LEDg_PIN;
  gpio.Mode = GPIO_MODE_OUTPUT_PP;
  gpio.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(LEDg_PORT, &gpio);

  // tx indication led
  gpio.Pin = LEDo_PIN;
  HAL_GPIO_Init(LEDo_PORT, &gpio);
}

void HAL_UART_MspDeInit(UART_HandleTypeDef *huart) {
  USARTx_FORCE_RESET();
  USARTx_RELEASE_RESET();

  HAL_GPIO_DeInit(USARTx_TX_PORT, USARTx_TX_PIN);
  HAL_GPIO_DeInit(USARTx_RX_PORT, USARTx_RX_PIN);

  HAL_DMA_DeInit(&uart_tx_dma);
  HAL_NVIC_DisableIRQ(USARTx_DMA_TX_IRQn);
//  HAL_NVIC_DisableIRQ(USARTx_IRQn);

  HAL_GPIO_DeInit(LEDg_PORT, LEDg_PIN);
}


// from it.c
void SysTick_Handler(void) {
    HAL_IncTick();
}

void USARTx_Handler(void) {
  HAL_UART_IRQHandler(&uart);
}

void USARTx_DMA_TX_IRQHandler(void) {
  HAL_DMA_IRQHandler(uart.hdmatx);
}