Random SPI data shifting at ~72kB/s throughput

[Musa]

Hello,

I am using nRF52 with ADS1292, and i am trying to sample at 8kHz with data throughput of 72kB/s, but some data is being randomly shifted giving me random spikes. This occurs on all available clock speeds to some degree. I am using Easy DMA. I am not getting any warnings or errors from the SPI driver as far as I can tell.

This issue does not occur at a lower data rate. Does this have something to do with overhead from the nRF SPIM drivers? I am also using I2C and other resources, but this also occurs with those additional resources disabled.

I'm trying to figure out what the limitation here is; is there a known limit on how many times you can call 'nrf_drv_spi_transfer' every second?

Thanks,

[MartinBL]

What kind of SPI clock frequency do you use? If I read the datasheet correctly maximum frequency is ~2MHz. If you go faster I suppose it is possible to get garbage bad data.

I think the input capacitance on the ADS1292 at 20pF is also relatively high. It might be worth a shot to configure the SPI pins in high drive to be able to source more current. You can do it by writing this after you call nrf_drv_spi_init():

nrf_gpio_cfg(p_config->sck_pin,
             NRF_GPIO_PIN_DIR_OUTPUT,
             NRF_GPIO_PIN_INPUT_CONNECT,
             NRF_GPIO_PIN_NOPULL,
             NRF_GPIO_PIN_H0H1,
             NRF_GPIO_PIN_NOSENSE);

If it still doesn't work, I think it could be interesting to see your code and PCB layout. You can upload it in confidence on our official support portal, MyPage if you prefer.