Question
HAL_UART_Transmit_DMA does not check if DMA is actually ready?
Hi,
I am using STM32Cube_FW_F4_V1.24.2. I noticed that HAL_UART_Transmit_DMA internally only checks the UART state (line 17) but completely ignores the return value of HAL_DMA_Start_IT (line 48). So what will happen if HAL_DMA_Start_IT returns HAL_BUSY for instance? In this case HAL_UART_Transmit_DMA would return HAL_OK although the start of the DMA transfer actually failed? In this case the data would never be sent. Or is this scenario impossible (by design)?
/**
* @brief Sends an amount of data in DMA mode.
* @note When UART parity is not enabled (PCE = 0), and Word Length is configured to 9 bits (M1-M0 = 01),
* the sent data is handled as a set of u16. In this case, Size must indicate the number
* of u16 provided through pData.
* @param huart Pointer to a UART_HandleTypeDef structure that contains
* the configuration information for the specified UART module.
* @param pData Pointer to data buffer (u8 or u16 data elements).
* @param Size Amount of data elements (u8 or u16) to be sent
* @retval HAL status
*/
HAL_StatusTypeDef HAL_UART_Transmit_DMA(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size)
{
uint32_t *tmp;
/* Check that a Tx process is not already ongoing */
if (huart->gState == HAL_UART_STATE_READY)
{
if ((pData == NULL) || (Size == 0U))
{
return HAL_ERROR;
}
/* Process Locked */
__HAL_LOCK(huart);
huart->pTxBuffPtr = pData;
huart->TxXferSize = Size;
huart->TxXferCount = Size;
huart->ErrorCode = HAL_UART_ERROR_NONE;
huart->gState = HAL_UART_STATE_BUSY_TX;
/* Set the UART DMA transfer complete callback */
huart->hdmatx->XferCpltCallback = UART_DMATransmitCplt;
/* Set the UART DMA Half transfer complete callback */
huart->hdmatx->XferHalfCpltCallback = UART_DMATxHalfCplt;
/* Set the DMA error callback */
huart->hdmatx->XferErrorCallback = UART_DMAError;
/* Set the DMA abort callback */
huart->hdmatx->XferAbortCallback = NULL;
/* Enable the UART transmit DMA stream */
tmp = (uint32_t *)&pData;
HAL_DMA_Start_IT(huart->hdmatx, *(uint32_t *)tmp, (uint32_t)&huart->Instance->DR, Size);
/* Clear the TC flag in the SR register by writing 0 to it */
__HAL_UART_CLEAR_FLAG(huart, UART_FLAG_TC);
/* Process Unlocked */
__HAL_UNLOCK(huart);
/* Enable the DMA transfer for transmit request by setting the DMAT bit
in the UART CR3 register */
SET_BIT(huart->Instance->CR3, USART_CR3_DMAT);
return HAL_OK;
}
else
{
return HAL_BUSY;
}
}Thanks in advance!
Kind regards,
Matthias