UARTE Clear Rx Buffer

Question

Hello, there, 
 
 I am trying to get the UARTE working on a custom nRF52840 board. In my setup, I am expecting a response to every transmission on UART. 
 
 Here's my setup code: 
 NRF_LIBUARTE_ASYNC_DEFINE(UARTE0, 0, 0, 0, NRF_LIBUARTE_PERIPHERAL_NOT_USED, 255, 3);
NRF_QUEUE_DEF(UARTERxBuffer, UARTE0RxBufferQueue, 4, NRF_QUEUE_MODE_NO_OVERFLOW);

//Initialising UARTE module
nrf_libuarte_async_config_t nrf_libuarte_async_config = {
 .tx_pin = JETFILE2_UART_TX_PIN,
 .rx_pin = JETFILE2_UART_RX_PIN,
 .baudrate = NRF_UARTE_BAUDRATE_115200,
 .parity = NRF_UARTE_PARITY_EXCLUDED,
 .hwfc = NRF_UARTE_HWFC_DISABLED,
 .timeout_us = 100,
 .int_prio = APP_IRQ_PRIORITY_LOW,
 };
 
 ret_code_t err_code = nrf_libuarte_async_init(&UARTE0, &nrf_libuarte_async_config, UARTE0EventHandler, (void *)&UARTE0);
 APP_ERROR_CHECK(err_code);

 nrf_libuarte_async_enable(&UARTE0); 
 
 Here's my event handler: 
 /*
 * Function: UARTE0EventHandler
 * Params: (Please refer to nRF documentation)
 * returns: None
 * Description: Handle for all UARTE events.
 */

void UARTE0EventHandler(void *context, nrf_libuarte_async_evt_t *p_evt) {
 nrf_libuarte_async_t *p_libuarte = (nrf_libuarte_async_t *)context;
 ret_code_t ret;

 switch (p_evt->type) {
 case NRF_LIBUARTE_ASYNC_EVT_ERROR:
 break;
 case NRF_LIBUARTE_ASYNC_EVT_RX_DATA:
 //Data received on UART. If a queue is available, "push" the Rx data into that queue.
 if (nrf_queue_available_get(&UARTE0RxBufferQueue) > 0) {
 UARTERxBuffer pushBuffer;
 pushBuffer.length = p_evt->data.rxtx.length;
 pushBuffer.p_data = p_evt->data.rxtx.p_data;

 //Push the data into the queue
 ret = nrf_queue_push(&UARTE0RxBufferQueue, &pushBuffer);
 APP_ERROR_CHECK(ret);
 }

 //As recommended by nRF(Infocenter -> nRF52 Series -> nRF52840 -> Specs -> Peripherals -> UARTE -> Reception), release the data.
 nrf_libuarte_async_rx_free(p_libuarte, p_evt->data.rxtx.p_data, p_evt->data.rxtx.length);
 nrf_drv_
 break;
 case NRF_LIBUARTE_ASYNC_EVT_TX_DONE:
 break;
 case NRF_LIBUARTE_ASYNC_EVT_OVERRUN_ERROR:
 break;
 default:
 break;
 }
} 
 
 Here's my application code: 
 void coreApplication(void) {
 char requestVersion[20] = {0x55, 0xA7, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x00, 0x03, 0x01, 0x00, 0x00};

 UARTE0TransmitData(requestVersion, 16);

 while (1) {
 uint8_t receivedData[30] = {0};
 //If a queue is not empty, read the content and process the data.
 if (nrf_queue_is_empty(&UARTE0RxBufferQueue) == false) {

 UARTERxBufferStruct buf;
 nrf_queue_pop(&UARTE0RxBufferQueue, &buf);

 //Reset the queue
 nrf_queue_reset(&UARTE0RxBufferQueue);

 memcpy(receivedData, buf.data, buf.length);

 //Toggle the LED
 bsp_board_led_invert(0);

 UARTE0TransmitData(requestVersion, 16);
 }

 nrf_delay_ms(100);
 NRF_LOG_FLUSH();
 }
} 
 
 While I am able to successfully transmit and receive, I want to know how to clear the Rx Buffer and reset the write position after each response from the other device. 
 
 Currently, the buffer wold just overflow, which is undesirable in my application. 
 
 Thank you.

Kenneth · Accepted Answer

The libuarte provide lossless asynchronous transfer. If you have specific requirements to how to flushing buffers (I assume you have control of when you can do this safely in case it is in the middle of a tx/rx transfer) you will either need to modify the library or use a different uart example as a starting point. 
 I do not quite understand how you can overflow the libuarte, you can provide several buffers, and as long as you can handle incomming data before all buffers are all full you should be safe. 
 Best regards, Kenneth

Kenneth · Answer

You are right that NRF_LIBUARTE_ASYNC_EVT_RX_DATA comes on timeout and on buffer getting full, in your case the 9th message will be split on two NRF_LIBUARTE_ASYNC_EVT_RX_DATA events (instead of only one). I am not aware of any way to avoid that no. The risk of manipulation the buffers is that you may lose bytes.

UARTE Clear Rx Buffer

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