nrf_serial_write not working

Question

This is my code: void send_serial_message(char *buffer, size_t length) { ret_code_t ret; //DEBUG NRF_LOG_INFO("tx buffer length = %d", length); for(int i=0; i app: tx buffer length = 8 app: AA app: FF app: 10 app: 08 app: F7 app: 10 app: 10 app: D8 app: serial return val: 0x0 The return code shows that it was "successful." However, the serial write is not working properly. Here is what I measure using a logic analyzer on the serial transmission pin: This is showing the 0xAA gets sent properly, but then the line goes low, and the rest of the sequence fails to transmit. What is happening??

ovrebekk · Accepted Answer

Hi 
 The TX_DONE event basically happens after every transmitted byte. When using the older UART peripheral there is no buffering happening in the UART peripheral itself, this is all handled by the driver. 
 If you want a callback when the TX buffer in the driver is empty I think you will need to change the nrf_serial.c implementation itself. 
 If you look at how NRF_DRV_UART_EVT_TX_DONE is handled you will see that it polls the TX queue to see if there are more bytes to send, and breaks otherwise: 
 case NRF_DRV_UART_EVT_TX_DONE:
{
 nrf_queue_t const * p_txq =
 p_serial->p_ctx->p_config->p_queues->p_txq;
 nrf_serial_buffers_t const * p_buffs =
 p_serial->p_ctx->p_config->p_buffers;

 event_handler(p_serial, NRF_SERIAL_EVENT_TX_DONE);
 size_t len = nrf_queue_out(p_txq, p_buffs->p_txb, p_buffs->tx_size);
 if (len == 0)
 {
 break;
 }

 ret = nrf_drv_uart_tx(&p_serial->instance, p_buffs->p_txb, len);
 ASSERT(ret == NRF_SUCCESS);
 break;
} 
 You will also note that the application event is triggered for every byte, by this call: 
 event_handler(p_serial, NRF_SERIAL_EVENT_TX_DONE); 
 By moving this call into the if (len == 0) check you should change the driver to only call the TX_DONE event when all the bytes are sent, which sounds like what you need. 
 Best regards Torbjørn

nrf_serial_write not working

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