SPIM fun (not!)

Question

Again, I'm having trouble with the driver library. Earlier when testing I had SPI working OK as a small standalone test , but now I want to add SPIM to my actual application. The application is based on the BLE sample template. 
 I've attached a cut down copy of my code and my sdk_config.h.. I'm guessing that the config file is screwed up as I had to hack it to remove some of the nrf legacy entries. 
 The test here is just trying to send some data over SPI. I toggle a debug gpio just to verify I'm looking in the right place. But I'm just seeing a handful of erratic pulses on the SCK line, and some regular clock-like pulses on the data line! (yes, the pinouts are correct) 
 So 
 Q1 Is there a sdk_config.h available with the old legacy drivers removed available? 
 Q2 What is the format of sdk_config.h? 
 Q3 I'm not sure what to do with the rx buffer? this is a tx only output 
 I've attached my config file and code, can you see anything fundamentally wrong with it? The end goal is to send 2-byte packets triggered by a timer via PPI. I already have the timer & PPI working, at the moment the PPI is just toggling a gpio as a test. 
 
 #define PIN_DBG 3
#define DAC_CS_PIN 31
#define DAC_SCK_PIN 26
#define DAC_SDI_PIN 29
#define DAC_SPI_INSTANCE 1
#define DAC_BUF_SIZE 16

//SPI master
#define SPI_INSTANCE 1 /**< SPI instance index. */
static const nrfx_spim_t spi = NRFX_SPIM_INSTANCE(SPI_INSTANCE); /**< SPI instance. */
static volatile bool spi_xfer_done; /**< Flag used to indicate that SPI instance completed the transfer. */
static uint8_t dac_buf[DAC_BUF_SIZE];
static uint8_t m_rx_buf[8]; /**< dummy RX buffer. */

static void idle_state_handle(void)
{
 if (NRF_LOG_PROCESS() == false)
 {
 nrf_pwr_mgmt_run();
 }
}

static void gpio_init(void)
{
 ret_code_t err_code;
 err_code = nrf_drv_gpiote_init();
 APP_ERROR_CHECK(err_code);
 nrf_drv_gpiote_out_config_t out_config = GPIOTE_CONFIG_OUT_SIMPLE(false); 
 err_code = nrf_drv_gpiote_out_init(PIN_DBG, &out_config);
	APP_ERROR_CHECK(err_code);
 nrf_drv_gpiote_in_config_t in_config = GPIOTE_CONFIG_IN_SENSE_TOGGLE(true);
 in_config.pull = NRF_GPIO_PIN_NOPULL;
 err_code = nrf_drv_gpiote_in_init(PIN_IN, &in_config, in_pin_handler);
	APP_ERROR_CHECK(err_code);
}

void spim_event_handler(nrfx_spim_evt_t const * p_event,
 void * p_context)
{
 spi_xfer_done = true;
 NRF_LOG_INFO("Transfer completed.");
}

/**@brief Function for application main entry.
 */
int main(void)
{
 uint16_t n; //TEST
 uint32_t err_code = NRF_SUCCESS;
 log_init();
 gpio_init();
 nrfx_spim_config_t spi_config = NRFX_SPIM_DEFAULT_CONFIG;
 spi_config.ss_pin = DAC_CS_PIN;
 spi_config.miso_pin = NRFX_SPIM_PIN_NOT_USED;
 spi_config.mosi_pin = DAC_SDI_PIN;
 spi_config.sck_pin = DAC_SCK_PIN;
 spi_config.frequency = NRF_SPIM_FREQ_8M;
 nrfx_spim_init(&spi, &spi_config, spim_event_handler, NULL);
 nrfx_spim_xfer_desc_t xfer_desc = NRFX_SPIM_XFER_TRX(&dac_buf, DAC_BUF_SIZE, m_rx_buf, 8);

 //SPI test
	// Fill the buffer and generate a waveform on the debug pin to check on the logic analyser
 for(n=0; n<16; n++)
 {
 dac_buf[n] = n;
 nrf_delay_us(1);
 nrfx_gpiote_out_clear(PIN_DBG);
 nrf_delay_us(1);
 nrfx_gpiote_out_set(PIN_DBG);
 }
 spi_xfer_done = false;
 APP_ERROR_CHECK(nrfx_spim_xfer(&spi, &xfer_desc, 0));
 while (!spi_xfer_done)
 {
 __WFE();
 } 
 nrfx_gpiote_out_clear(PIN_DBG);
 // Enter main loop.
 for (;;)
 idle_state_handle();
}

 
 sdk_config.h

hmolesworth · Accepted Answer

You may be seeing a 'scope alias issue, but even if not using the SPI at 8MHz really requires high drive outputs; these must be set after initialising the SPI: 
 nrf_gpio_cfg(DAC_CS, NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
 nrf_gpio_cfg(DAC_SDI, NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
 nrf_gpio_cfg(DAC_SCK, NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE); 
 The Rx stuff is redundant, just use null and 0 thus: 
 nrfx_spim_xfer_desc_t xfer_desc = NRFX_SPIM_XFER_TRX(&dac_buf, DAC_BUF_SIZE, NULL, 0); 
 If there are still issues, try dropping to clock to 1MHz just to check the capacitance on the connecting leads are not too high, Leads more than a few inches (100mm) can cause transmission issues on the SCK at the DAC if it happens to be a high-speed DAC; in that case a damping or termination resistor will be required. Usually high-drive alone fixes that though.

SPIM fun (not!)

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