Check UART transmit complete in nRF52832

RE: Check UART transmit complete in nRF52832

chianglin — Wed, 20 Mar 2019 07:34:33 GMT

Hi,

I had complete the implement of RS485 interface.

Thank you for your support.

Chianglin

RE: Check UART transmit complete in nRF52832

Jørgen Holmefjord — Tue, 19 Mar 2019 09:16:23 GMT

Yes, you do.

If you look at the implementation in the library (app_uart_fifo.c), you can see that the whenever a NRF_DRV_UART_EVT_TX_DONE event is received from the driver (indicating that a byte have been successfully transmitted) it will pull a new byte from the FIFO and transmit this, or send the APP_UART_TX_EMPTY event if no more bytes are present in the FIFO:

case NRF_DRV_UART_EVT_TX_DONE:
    // Get next byte from FIFO.
    if (app_fifo_get(&m_tx_fifo, tx_buffer) == NRF_SUCCESS)
    {
        (void)nrf_drv_uart_tx(&app_uart_inst, tx_buffer, 1);
    }
    else
    {
        // Last byte from FIFO transmitted, notify the application.
        app_uart_event.evt_type = APP_UART_TX_EMPTY;
        m_event_handler(&app_uart_event);
    }

RE: Check UART transmit complete in nRF52832

awneil — Mon, 18 Mar 2019 17:37:40 GMT

[quote userid="14926" url="~/f/nordic-q-a/44934/check-uart-transmit-complete-in-nrf52832/176746"]you will get a APP_UART_TX_EMPTY event when all bytes have been transmitted.[/quote]

Do you?

Or do you get that event when the last byte has been taken out of the FIFO, and loaded into the UART for transmission?

For turning round a half-duplex line (such as chianglin's RS485), you need to know the actual end of transmission - ie, when the final stop bit has left the shift register ...

RE: Check UART transmit complete in nRF52832

Jørgen Holmefjord — Mon, 18 Mar 2019 14:05:26 GMT

Like I wrote in my previous answer, you will get a APP_UART_TX_EMPTY event when all bytes have been transmitted. You can set a flag in the event handler when you receive this event, and use this flag to no the switching between TX and RX.

RE: Check UART transmit complete in nRF52832

chianglin — Mon, 18 Mar 2019 13:50:37 GMT

Hi Jørgen,

Thank you for your explain.

Actually, I use UART interface to send / receive RS485 data.

Because RS485 is working in half duplex transceiver mode. I need to know UART is complete send all data and switch to receive mode, so Nordic can receive data from RS485 mode.

Would you please tell me how can I do this job?

Thank you,

Chianglin

RE: Check UART transmit complete in nRF52832

Jørgen Holmefjord — Mon, 18 Mar 2019 13:06:50 GMT

Hi,

When you call printf, all chars in the string will be put into the app_uart FIFO by multiple calls to app_uart_put(), and the library will start processing the FIFO. Then printf returns, all chars have been put into the FIFO. Whenever all bytes have been transmitted and the app_uart FIFO is empty, you will receive a APP_UART_TX_EMPTY event in the event handler. If you have added more bytes to the FIFO in the meantime, you will not receive an event until these bytes have been transmitted as well. There is no other functionality in the library to know when a transfer is completed.

Best regards,
Jørgen