SPIM fun (not!)

RE: SPIM fun (not!)

hmolesworth — Tue, 21 Apr 2020 19:45:44 GMT

Ah, sdk_config.h - the bane of developers. I put stuff like this at the top of sdk_config.h:

#if defined(FEATURE_NO_32_KHZ_CRYSTAL)
#define NRFX_CLOCK_CONFIG_LF_SRC         0
#define CLOCK_CONFIG_LF_SRC              0
#define NRF_SDH_CLOCK_LF_SRC             0
#define NRF_SDH_CLOCK_LF_RC_CTIV        16
#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV    2
#define NRF_SDH_CLOCK_LF_ACCURACY        1 // <1=> NRF_CLOCK_LF_ACCURACY_500_PPM
#endif

#if defined(FEATURE_SPIM2)
#define SPIM_PRESENT               1
#define NRF_SPI_ENABLED            1//0
#define NRFX_SPI_ENABLED           1//0
#define NRF_SPIM2_ENABLED          1//0
#define NRFX_SPIM_ENABLED          1//0
#define NRFX_SPIM2_ENABLED         1//0
#endif

#if defined(FEATURE_SPIM3)
#define SPIM_PRESENT               1
#define NRF_SPI_ENABLED            1//0
#define NRFX_SPI_ENABLED           1//0
#define NRF_SPIM3_ENABLED          1//0
#define NRFX_SPIM_ENABLED          1//0
#define NRFX_SPIM3_ENABLED         1//0
#define NRFX_SPIM_EXTENDED_ENABLED 1//0
#endif

Then in project Preprocessro definitions FEATURE_SPIM2 etc; not pretty but it save lots of time trying to do it "properly" .. these settings give you DMA via the Nordic drivers

RE: SPIM fun (not!)

Nick_RA — Tue, 21 Apr 2020 16:55:39 GMT

OK - humble pie time! Yes it was aliasing as the sampling rate on my LA was sett too low for some reason 😞 The drive rate will be useful though... It's working fine as-is but would be good to set it anyway so not a wasted exercise.

Do you have any info on the sdk config? The one I'm using has been hacked about and may cause issues down the line. For example I can't see any option for setting EasyDMA, I may not need it as I'm only sending 2 bytes at a time but every little helps as the CPU can potentially get quite busy at times (I have a SoftDevice running, a SD card connected by SPI, this DAC output and a 5kbps Manchester decoder potentially all running concurrrently)

Thanks

Nick

RE: SPIM fun (not!)

hmolesworth — Tue, 21 Apr 2020 15:30:27 GMT

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.