UARTE: Synchronous usage - How to poll for data (nrfx)

[RoyCreemers]

I'm using the nrfx drivers of SDK 15.3.0 and want to poll for data using a synchronous UART. In order to check for data, I use the 'nrfx_uarte_rx_ready' function. However, this function always returns false, indicating no data is available. 

See the example code below. I would like to print a '*' each time a character is entered.

Example project:

void Write(nrfx_uarte_t* instance, char* d, uint8_t size)
{
uint8_t data[255];
memcpy(data, d, size);
uint32_t result = nrfx_uarte_tx(instance, data, size);
}

bool HasData(nrfx_uarte_t* instance)
{
return nrfx_uarte_rx_ready(instance);
}

int main(void)
{
bsp_board_init(BSP_INIT_LEDS);
nrfx_uarte_t instance = NRFX_UARTE_INSTANCE(0);
nrfx_uarte_config_t config = NRFX_UARTE_DEFAULT_CONFIG;
config.pselrxd = NRF_GPIO_PIN_MAP(0, 8);
config.pseltxd = NRF_GPIO_PIN_MAP(0, 6);
config.hwfc = NRF_UARTE_HWFC_DISABLED;
config.parity = NRF_UARTE_PARITY_EXCLUDED;
config.baudrate = NRF_UARTE_BAUDRATE_115200;
uint32_t result = nrfx_uarte_init(&instance, &config, NULL);
Write(&instance, "Hello", 6);

while (true)
{
if (HasData(&instance))
Write(&instance, "*", 2);
}
}

[Jørgen Holmefjord]

Hi,

You still need to setup a buffer and start the receive operation to get any data. The following code should do what you want:

uint8_t rx_buff;

void Write(nrfx_uarte_t* instance, char* d, uint8_t size)
{
    uint8_t data[255];
    memcpy(data, d, size);
    uint32_t result = nrfx_uarte_tx(instance, data, size);
}

bool HasData(nrfx_uarte_t* instance)
{
    ret_code_t ret = nrfx_uarte_rx_ready(instance);
    if(ret)
    {
        nrfx_uarte_rx(instance, &rx_buff, 1);
    }
    return ret;
}

int main(void)
{
    bsp_board_init(BSP_INIT_LEDS);
    nrfx_uarte_t instance = NRFX_UARTE_INSTANCE(0);
    nrfx_uarte_config_t config = NRFX_UARTE_DEFAULT_CONFIG;
    config.pselrxd = NRF_GPIO_PIN_MAP(0, 8);
    config.pseltxd = NRF_GPIO_PIN_MAP(0, 6);
    config.hwfc = NRF_UARTE_HWFC_DISABLED;
    config.parity = NRF_UARTE_PARITY_EXCLUDED;
    config.baudrate = NRF_UARTE_BAUDRATE_115200;
    uint32_t result = nrfx_uarte_init(&instance, &config, NULL);
    nrfx_uarte_rx(&instance, &rx_buff, 1);
    Write(&instance, "Hello", 6);
    

    while (true) 
    {
        if (HasData(&instance))
        {
            Write(&instance, "*", 2);
        }
    }
}

Best regards,
Jørgen

[RoyCreemers]

This example only works in case there is actual data coming. In case there is no data to receive, the example blocks in nrfx_uarte_rx. Is there any way I can query whether or not there is actual data, before reading it? (Goal is to implement synchronous read with timeout in case no data is available)

[Jørgen Holmefjord]

If you switch to using the nrfx_uart driver (without EasyDMA support), you should be able to do this by calling nrfx_uart_rx_enable() to enable RX and poll using nrfx_uart_rx_ready(). I do not see the purpose of the function nrfx_uarte_rx_ready in the nrfx_uarte driver without any rx_enable functions. Like you say, nrfx_uarte_rx will block until the data is received.

[RoyCreemers]

Thanks for the response. I will look into the nrfx_uart driver. I started using the uarte driver since I'm developing a HAL layer where multiple instances can be instantiated (c++), and the nrfx uart only supports a single uart