Reading from slave chip (ADS1293) through SPI

[Konrad213]

Hi everyone!

I'm trying to read a register from the ADS1293 chip by using SPI but have been stuck for a good two days. The very basic code I have is right below:

#define SPI_INSTANCE   0

static uint8_t tx;
static uint8_t rx;

static const nrf_drv_spi_t m_spi_master_0 = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE);

void ADS_init( void )
{
    nrf_drv_spi_config_t const spi_config =
    {
        .sck_pin        = 27,
        .mosi_pin       = 6,
        .miso_pin       = 42,
        .ss_pin         = 44,
        .irq_priority   = APP_IRQ_PRIORITY_LOW,
        .orc            = 0xFF,
        .frequency      = NRF_DRV_SPI_FREQ_4M,
        .mode           = NRF_DRV_SPI_MODE_0,
        .bit_order      = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST, 
    };
    ret_code_t err_code = nrf_drv_spi_init(&m_spi_master_0, &spi_config, NULL, NULL);
    //SEGGER_RTT_printf(0, nrf_strerror_get(err_code));
     
}

uint8_t Read_reg(uint8_t addr)
{ 
  tx = ADS1293_READ_BIT | addr;
  ret_code_t err_code = nrf_drv_spi_transfer(&m_spi_master_0, &tx, 1, &rx, 1);
  SEGGER_RTT_printf(0, nrf_strerror_get(err_code));
  return rx;
}

There are two things I'm not 100% sure about:

1) If the pins I'm using are correct. Is there any way to make sure that the pins I'm using are correct that is simpler than managing to read the register on the ADS? Here's how they are connected:

 NRF      ADS
P0.19 -> SDO
P0.20 -> SDI
P0.04 -> SCLK
P0.03 -> CSB

2) If the way I'm using nrf_drv_spi_transfer is correct for the ADS. If I understand correctly what's on page 37 in their documentation I should send in 8 bits and will receive 8 bits and I do this by sending in the uint8_t tx (address but set the first bit to 1) and uint8_t rx. 

When I do this I get the NRF_SUCCESS code but the data received is 0x00 and is supposed to be 0x02 for the register I'm trying. I'm really new to this so I have really no idea what I should be doing right now.

[Simonr]

Hi

It seems like you've mixed up the SPI pin configuration, as you should refer to the pin configuration chapter when configuring pins, and not the pin assignments. The sck_pin, mosi_pin, miso_pin, and ss_pin configured like this for the setup you're describing.

        .sck_pin        = 4,
        .mosi_pin       = 20,
        .miso_pin       = 19,
        .ss_pin         = 3,

Best regards,

Simon

[Konrad213]

Thank you! Now the execution gets stuck at nrf_drv_spi_transfer which never returns anything do you know any potential reasons for that?

[awneil]

Again, have you used an oscilloscope to see what's happening on the wires?

Have you used the debugger to find exactly where it's getting stuck within the software?

[Konrad213]

Thanks for the answer! Won't have access to an oscilloscope for a couple of days, will do so as soon as I have but I'm hoping I can get past this issue before that. The execution gets stuck in this while loop (part of nrfx_spim.c):

 if (!p_cb->handler)
    {
        while (!nrf_spim_event_check(p_spim, NRF_SPIM_EVENT_END)){}

Here's nrf_spim_event_check (part of nrf_spim.h):

 

__STATIC_INLINE bool nrf_spim_event_check(NRF_SPIM_Type * p_reg,
                                          nrf_spim_event_t spim_event)
{
    return (bool)*(volatile uint32_t *)((uint8_t *)p_reg + (uint32_t)spim_event);
}

[Konrad213]

I used an oscilloscope and changed the code slightly but still the same behavior as mentioned below. I used an arduino to talk to the ADS chip and it worked fine. It looks like the output to the slave select pin isn't happening at all (voltage stays same on oscilloscope) when using the nrf chip vs the arduino. Any ideas?

static uint8_t tx[2];
static uint8_t rx[2];

static const nrfx_spim_t m_spi_master_0 = NRFX_SPIM_INSTANCE(SPI_INSTANCE);

void ADS_init( void )
{
    nrfx_spim_config_t const spi_config =
    {
        .sck_pin        = 4,
        .mosi_pin       = 22,
        .miso_pin       = 23,
        .ss_pin         = 3,
        .irq_priority   = APP_IRQ_PRIORITY_LOW,
        .orc            = 0xFF,
        .frequency      = NRF_SPIM_FREQ_4M,
        .mode           = NRF_SPIM_MODE_2,
        .bit_order      = NRF_SPIM_BIT_ORDER_MSB_FIRST, 
    };
    ret_code_t err_code = nrfx_spim_init(&m_spi_master_0, &spi_config, NULL, NULL);
    SEGGER_RTT_printf(0, nrf_strerror_get(err_code));
     
}

uint8_t Read_reg(uint8_t addr)
{ 

  tx[0] = addr | ADS1293_READ_BIT; 
  tx[1] = 0x00; 
  nrfx_spim_xfer_desc_t xfer_desc = NRFX_SPIM_XFER_TRX(tx, 2, rx, 2);
  nrf_gpio_pin_clear(3);
  ret_code_t err_code = nrfx_spim_xfer(&m_spi_master_0, &xfer_desc, 0);
  nrf_gpio_pin_set(3);
  SEGGER_RTT_printf(0, nrf_strerror_get(err_code));
  return rx[1];

}