Chapter 2. API Reference
// Driver library function used to receive uxWantedBytes from an Rx buffer
// that is filled by a UART interrupt. If there are not enough bytes in the
// Rx buffer then the task enters the Blocked state until it is notified that
// more data has been placed into the buffer. If there is still not enough
// data then the task re-enters the Blocked state, and xTaskCheckForTimeOut()
// is used to re-calculate the Block time to ensure the total amount of time
// spent in the Blocked state does not exceed MAX_TIME_TO_WAIT. This
// continues until either the buffer contains at least uxWantedBytes bytes,
// or the total amount of time spent in the Blocked state reaches
// MAX_TIME_TO_WAIT – at which point the task reads however many bytes are
// available up to a maximum of uxWantedBytes.
size_t xUART_Receive( uint8_t *pucBuffer, size_t uxWantedBytes )
{
size_t uxReceived = 0;
TickType_t xTicksToWait = MAX_TIME_TO_WAIT;
TimeOut_t xTimeOut;
// Initialize xTimeOut. This records the time at which this function
// was entered.
vTaskSetTimeOutState( &xTimeOut );
// Loop until the buffer contains the wanted number of bytes, or a
// timeout occurs.
while( UART_bytes_in_rx_buffer( pxUARTInstance ) < uxWantedBytes )
{
// The buffer didn't contain enough data so this task is going to
// enter the Blocked state. Adjusting xTicksToWait to account for
// any time that has been spent in the Blocked state within this
// function so far to ensure the total amount of time spent in the
// Blocked state does not exceed MAX_TIME_TO_WAIT.
if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) != pdFALSE )
{
//Timed out before the wanted number of bytes were available,
// exit the loop.
break;
}
// Wait for a maximum of xTicksToWait ticks to be notified that the
// receive interrupt has placed more data into the buffer.
ulTaskNotifyTake( pdTRUE, xTicksToWait );
}
// Attempt to read uxWantedBytes from the receive buffer into pucBuffer.
// The actual number of bytes read (which might be less than
// uxWantedBytes) is returned.
uxReceived = UART_read_from_receive_buffer( pxUARTInstance,
pucBuffer,
uxWantedBytes );
return uxReceived;
}
Return If timeout has occurred, pdTRUE is returned. Otherwise pdFALSE is returned and pxTicksToWait
is updated to reflect the number of remaining ticks.
See https://www.FreeRTOS.org/xTaskCheckForTimeOut.html
Parameters
• pxTimeOut: The time status as captured previously using vTaskSetTimeOutState. If the timeout
has not yet occurred, it is updated to reflect the current time status.
• pxTicksToWait: The number of ticks to check for timeout i.e. if pxTicksToWait ticks have
passed since pxTimeOut was last updated (either by vTaskSetTimeOutState() or xTaskCheckFor-
TimeOut()), the timeout has occurred. If the timeout has not occurred, pxTicksToWait is updated
Espressif Systems 879
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