Problems to manage SPI pins to communicate with the slave.

RE: Problems to manage SPI pins to communicate with the slave.

Jørgen Holmefjord — Mon, 13 Nov 2017 08:23:13 GMT

Yes, normally SPI slave select pin is active low. Then you need to interchange the functions.

RE: Problems to manage SPI pins to communicate with the slave.

nemunoz — Fri, 10 Nov 2017 20:21:55 GMT

Sorry but I find a mistake in the code. The clear and set functions are in the wrong positions. To fix it you must interchange them.

RE: Problems to manage SPI pins to communicate with the slave.

nemunoz — Thu, 02 Nov 2017 19:11:30 GMT

yeah! It works! Thank you so much! I didn't know I could do that!

I'm sorry for answer you so late but I was also having problems to use the slave through SPI (an independent problem) so couldn't try your solution before.

RE: Problems to manage SPI pins to communicate with the slave.

Jørgen Holmefjord — Fri, 27 Oct 2017 09:30:59 GMT

The NRF_DRV_SPI_EVENT_DONE event is passed to the event handler when the transfer is doen. The Slave Select pin is optional in the SPI master driver config struct. If you set this pin to NRF_SPI_PIN_NOT_CONNECTED, you can control the SS/CS pin yourself. You can then check if the MISO pin goes low before starting the SPI transfer. Something like the below code should work:

void spi_event_handler(nrf_drv_spi_evt_t const * p_event, void * p_context)
{
	nrf_gpio_pin_clear(SPI_SS_PIN);
}

void spi_transfer()
{
	nrf_gpio_pin_set(SPI_SS_PIN);
	while (nrf_gpio_pin_read(SPI_MISO_PIN))
	{
	}
	APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, m_tx_buf, m_length, m_rx_buf, m_length));
}

void main()
{
	nrf_gpio_cfg_output(SPI_SS_PIN);
	
	nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
    spi_config.ss_pin   = NRF_SPI_PIN_NOT_CONNECTED;
    spi_config.miso_pin = SPI_MISO_PIN;
    spi_config.mosi_pin = SPI_MOSI_PIN;
    spi_config.sck_pin  = SPI_SCK_PIN;
	
    APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL));
	
	spi_transfer();
	
	while(1)
	{
		
	}
}

RE: Problems to manage SPI pins to communicate with the slave.

nemunoz — Thu, 26 Oct 2017 17:30:15 GMT

The event handler is the third parameter of nrf_drv_spi_init function (the event type is nrf_drv_spi_evt_handler_t)

The slave device is a radio frecuency chip CC1125 and the user's guide, in the page 8 first paragraph, says:

"When CSn is pulled low, the MCU must wait until CC112X SO pin goes low before starting to transfer the header byte. This indicates that the crystal is stable. Unless the chip was just reset or was in SLEEP or XOFF state, or the XOSC configuration has been altered, the SO pin will always go low immediately after pulling CSn low."

RE: Problems to manage SPI pins to communicate with the slave.

Jørgen Holmefjord — Thu, 26 Oct 2017 12:41:49 GMT

I'm sorry but I don't understand your questions. What event are you talking about? Where does the requirement that MISO needs to be driven low come from? If you are using the SPI driver, this will handle the pins for you.