RE: Get the available space of the UART tx buffer

Jørgen Holmefjord — Thu, 11 Mar 2021 13:48:21 GMT

Hi,

If you are using the unmodified ble_app_uart_c example with app_uart_fifo for sending data over UART, you should get a NRF_ERROR_NO_MEM return code from app_uart_put when the FIFO TX buffer configured for app_uart is full. The FIFO is not available outside of the library, but you can create a function to return the available size like this:

uint32_t app_uart_get_tx_fifo_size(void)
{
    return (m_tx_fifo.buf_size_mask + 1) - FIFO_LENGTH(m_tx_fifo);
}

Note that app_uart transmits a single byte over UART at a time. If you need to transfer large amounts of data over UART quickly, you may be better off with using the UARTE driver with EasyDMA support, or the new libUARTE library. These allows you to send larger chunks of data over UARTE (up to 65535 bytes for nRF52840) directly from RAM, without any CPU intervention.

Best regards,
Jørgen