NRF51 Uart Overrun

[Epimeth]

Hi,

I use a GPS Modul to send data via uart to the NRF 51 and then I send the string via SPI and fatfs to the SD CArd.

I see the LED4 blinking and during the debugging I can see the Uart has an overrun event. The Uart has no flow control and a baud rate from 9600.

The overrun is calling during the fatfs. So I expect losing data by writing to the SD CArd, but all data is written without any failure.

I use  normal libary, no softdevice and calling the fatfs from the main loop,

What means the LED 4, if it blinking and why i have an uart overrun event but nothing happen with the data?

[Turbo J]

It may be hard to spot with the naked eye, but you should get at least a failed checksum.

In case your code silently drops NMEA sentences with a wrong check sum, the result will look and also likely work quite acceptable.

Note: The reason you get UART overruns is that the SD card can take quite some time to write a sector. Expected worst case timing is in the 300ms to 1second range, and *much* longer if the card was badly fragmented.

[Epimeth]

You can see this behaviour in the example fafts sdk12.3, too.

The Blinking LED 4 comes from this pieces of code, app_sdcard.c

__STATIC_INLINE void sdc_spi_transfer(uint8_t const * const p_txb,
                                      uint8_t tx_len,
                                      uint8_t * const p_rxb,
                                      uint8_t rx_len)
{
    SDC_CS_ASSERT();
    ret_code_t err_code = nrf_drv_spi_transfer(&m_spi, p_txb, tx_len, p_rxb, rx_len);
    APP_ERROR_CHECK(err_code);
}

with SDC_CS_ASSERT() you call from nrf_gpio.h

nrf_gpio_port_out_clear(reg, 1UL << pin_number);

It is possible after calling nrf_drv_spi_transfer to return  back to main.c, without waiting? Maybe with a spi eventhandler?

Because i think it is running in blocking mode.

[Turbo J]

That would require something like an RTOS, and might be too much for the limited RAM on NRF51, but YMMV.

The FATFS code is rather complex and will likely only work properly when called from main(). It also expects disk read and write calls to be blocking.

The only other way is to use a rather large UART buffer for the GPS data.