An issue in NRF51822 custom board as spi slave with BLE

Question

Hello there,

I'm trying to use my NRF51822 custom board as spi slave with BLE that sending whatever received from the master. I'm using MSP430FR5994 as the master.

I'm using 110 softdevice and SDK v10. I tried to combine both BLE peripheral and spi slave examples from the SDK. BLE code works fine (received all zeros value using N RFconnect) but spi slave does not.

I tried to debug the master spi pins using the oscilloscope. I can see the master source the clock when the CS goes low, but this happens only when the NRF51822 custom board is not connected to the master. When I connected the NRF51822 custom board, the CS never goes low ( it always high even when the Master drives it low to start the spi communication ).

I sat the clock speed to 1MHz in the master because from my search in this forum I knew that maximum clock speed fro spi slave for nrf51822 is 2MHz. Also, I set up the spi mode, bit order to be the same in both master and slave.

I'm pretty sure I miss something in the NRF51822 configuration or my logic is wrong. Do I need to configure the clock in the NRF51822 ?

Any help would be highly appreciated.

Here is a snippet of my code:

// setting up the spi pins
#define 	NRF_GPIO_PIN_MAP(port, pin)   ((port << 5) | (pin & 0x1F))
#define SPIS_SCLK_PIN NRF_GPIO_PIN_MAP(0, 3)   // pin P03
#define SPIS_MOSI_PIN NRF_GPIO_PIN_MAP(0, 1)   //pin P01
#define SPIS_MISO_PIN NRF_GPIO_PIN_MAP(0, 2)   //pin P02
#define SPIS_CS_PIN NRF_GPIO_PIN_MAP(0, 4)    //pin P03

int main(void)
{

    uint32_t err_code;
    uint8_t i;
    
    // Initialize spis
    err_code = spi_slave_init();
    APP_ERROR_CHECK(err_code);

    // Initialize BLE
    ble_stack_init();
    gap_params_init();
    advertising_init();
    services_init();
    // Start execution.
    err_code = ble_advertising_start(BLE_ADV_MODE_FAST);
    APP_ERROR_CHECK(err_code);

    // Enter main loop.
    while(1)
    {
        nrf_delay_ms(10000);
        for(i=0;i<CHARACTERISTIC_SIZE;i++)
        {
             char1_data[i] = m_rx_buf[i]; // update BLE data using RX buffer
        }
        err_code = custom_service_update_data(m_conn_handle,char1_data);
        APP_ERROR_CHECK(err_code);
    }
}


uint32_t spi_slave_init(void)
{
    uint32_t              err_code;
    nrf_drv_spis_config_t spis_config = NRF_DRV_SPIS_DEFAULT_CONFIG(SPIS_INSTANCE_NUMBER);

    spis_config.miso_pin        = SPIS_MISO_PIN;
    spis_config.mosi_pin        = SPIS_MOSI_PIN;
    spis_config.sck_pin         = SPIS_SCLK_PIN;
    spis_config.csn_pin         = SPIS_CS_PIN;
    spis_config.mode            = NRF_DRV_SPIS_MODE_0;
    /*
    NRF_DRV_SPIS_MODE_0   -----> (CPOL = 0, CPHA = 0)
    NRF_DRV_SPIS_MODE_1   -----> (CPOL = 0, CPHA = 1)
    NRF_DRV_SPIS_MODE_2   -----> (CPOL = 1, CPHA = 0)
    NRF_DRV_SPIS_MODE_3   -----> (CPOL = 1, CPHA = 1)
    */
    spis_config.bit_order       = NRF_DRV_SPIS_BIT_ORDER_MSB_FIRST;
    spis_config.def             = DEF_CHARACTER;
    spis_config.orc             = ORC_CHARACTER;

    err_code = nrf_drv_spis_init(&m_spis, &spis_config, spi_slave_event_handle);
    APP_ERROR_CHECK(err_code);

    //Initialize buffers.
    spi_slave_buffers_init(m_tx_buf, m_rx_buf, (uint16_t)TX_BUF_SIZE);

    //Set buffers.
    err_code = nrf_drv_spis_buffers_set(&m_spis, m_tx_buf, sizeof(m_tx_buf), m_rx_buf, sizeof(m_rx_buf));
    APP_ERROR_CHECK(err_code);

    return NRF_SUCCESS;
}