Missing APP_UART_TX_EMPTY event

[Mattias]

Hi!

I am working with an application were two nRF52832 shall communicate over UART in half-duplex 1-wire mode (similar to what is described here but I use different pins for Tx/Rx: devzone.nordicsemi.com/.../). The FIFO version of app_uart (app_uart_fifo.c) and SDK 13.0.0 is used.

APP_UART_TX_EMTY is used to check that data been sent before Tx pin is switched to input mode. The problem I am facing is that I don't get the event if I just use app_uart_put() to transmit single data bytes from unit 1 to unit 2. But if I add printf("\r\n") the event occur as expected. I have verified with oscilloscope that first data byte is sent. Code snippets are shown below.

    void uart_event_handler(app_uart_evt_t * p_event)
    {
        if (p_event->evt_type == APP_UART_COMMUNICATION_ERROR)
        {
            APP_ERROR_HANDLER(p_event->data.error_communication);
        }
        else if (p_event->evt_type == APP_UART_FIFO_ERROR)
        {
            APP_ERROR_HANDLER(p_event->data.error_code);
        }
        else if (p_event->evt_type == APP_UART_TX_EMPTY)
        {
            tx_empty_flag = true;
        }
        else if (p_event->evt_type == APP_UART_DATA_READY)
        {
            data_ready_flag = true;
        }
    }
    
    
    
    while (true)
    {
       while (app_uart_put('A') != NRF_SUCCESS);
       printf("\r\n");  // no APP_UART_TX_EMPTY is received in uart_event_handler if line deleted 
    
       while (tx_empty_flag != true );
       tx_empty_flag = false;
       disable_tx();  
    
    }

Could anyone explain this?

Thanks in advance, Mattias

[Mattias]

I temporary gave up the event controlled approach and implemented a delay based version instead. Instead of waiting for the empty flag I added a 100 us delay after each reconfiguration of Tx pin. This works fine and is actually good enough at the moment since I am in a proof of concept phase with this project. But of course I need to understand and solve this in the end.

/* Currently my code looks like this and it works */
enable_tx();
while (app_uart_put(0x7E) != NRF_SUCCESS);
disable_tx(); // function now includes a 100 us delay after reconfiguration