SPI Slave readout returns always 0

[Neum_d]

Hi,

i'm trying to readout the who_am_i register of SPI slave ST lis2hh12 (a MEMS sensor). I followed the spi-example found in examples/peripheral/spi of SDK 15.3.0.

I modified the parameters of spi_config, but it has no effect at all:

uint8_t       m_tx_buf[3];
uint8_t       m_rx_buf[3];

nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
spi_config.ss_pin   = SPI_SS_PIN;
spi_config.miso_pin = SPI_MISO_PIN;
spi_config.mosi_pin = SPI_MOSI_PIN;
spi_config.sck_pin  = SPI_SCK_PIN;
spi_config.orc = 0xFF;
spi_config.frequency = NRF_DRV_SPI_FREQ_2M;
spi_config.mode = NRF_DRV_SPI_MODE_0;
spi_config.bit_order = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST;

uint32_t init_error_code=nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL);
m_tx_buf[0]=0x80|LIS2HH12_WHO_AM_I;
m_tx_buf[1]=0xFF;
m_rx_buf[0]=0xFF;
m_rx_buf[1]=0xAA;
spi_xfer_done=false;
uint32_t transfer_error_code=nrf_drv_spi_transfer(&spi, m_tx_buf, 1, m_rx_buf, 2);
while (!spi_xfer_done)
{
  __WFE();
}

The rx_buf is at the end always 0x00 0x00, i expected something like 0x00 0x41. init_error_code and transfer_error_code have the value NRFX_SUCCESS.

[Kenneth]

Not sure why you are populating m_rx_buf[] with values, since that is the values received on MISO. Do you have a logic analyzer to observe data on the SPI lines?

[Neum_d]

I populate m_rx_buf[] to see, if its content changes. Yes, the content changes. Unfortunately, I do not have a logic analyzer.

[Kenneth]

I recommend to get a logic analyzer and/or oscilloscope so you may observe the physical pins. For test if you connect MISO to MOSI, you likely will see that m_rx_buf == m_tx_buf.

Kenneth

[Neum_d]

Thank you very much! I borrowed a 2-channel oscilloscope from a friend and as i started to connect the oscilloscope-channels to the pins CS and SCK, i saw that i used the wrong pins!