How can I check printf's buffer?

[Nick_RA]

Hi

Using nRF52DK + SDK17.1 + S112

I have retarget enabled & using printf to output over UART (no DMA)

What's the best way to check if printf is busy outputting data? I want to disable the UART after a print to save power but need to wait until all characters have been transmitted and the UART is empty.

Nick

[Vidar Berg]

Hi Nick,

The app uart libary used by retarget.c does not expose an API to check if there are pending TX transfers. So, the simplest solution is probably to add a small busy-wait (nrf_delay_ms(), etc) before you disable the peripheral. Otherwise, you would have to modify app_uart_fifo.c to include a function to check if there are bytes left in the TX fifo.

Possibly something like this:

bool app_uart_tx_in_progress(void)
{
    bool fifo_empty = false;
    uint32_t size;

    if (FIFO_LENGTH(m_tx_fifo) == 0)
    {
        fifo_empty = true;
    }
    
    return (fifo_empty == false);
}

Best regards,

Vidar

[Nick_RA]

OK thanks. I'll probably use a housekeeping timer ISR anyway so I'll put a timeout on it which I can reset when I print.