Add initialization sequence to SPIM interface

RE: Add initialization sequence to SPIM interface

haakonsh — Thu, 04 May 2023 07:28:44 GMT

[quote user="kfxkaplan"]This did the trick, thank you so much for your help![/quote]

I'm glad to hear it worked out, let me know if you do find any issues.

One scenario you might want to be aware of is if an ISR executes between sending the start-condition and triggering the SPIM start task, then you will likely experience similar issues as before. You should therefore make your application tolerant to this SPI fault.

RE: Add initialization sequence to SPIM interface

kfxkaplan — Wed, 03 May 2023 14:47:22 GMT

This did the trick, thank you so much for your help!

RE: Add initialization sequence to SPIM interface

haakonsh — Wed, 03 May 2023 08:36:47 GMT

SCK and MOSI will return to their last configured state when the SPIM peripheral is disabled, that might be what's happening.

Try calling nrf_gpio_pin_clr(RFID_SPI_SCK_PIN) and nrf_gpio_pin_clr(RFID_SPI_MOSI_PIN), after you've enabled the SPIM. The pins should not immidiately change state as the GPIO peripheral is overridden by the SPIM peripheral, for as long as the SPIM peripheral is enabled.

RE: Add initialization sequence to SPIM interface

kfxkaplan — Tue, 02 May 2023 17:59:16 GMT

Thanks for the feedback haakonsh! I implemented the steps as follows

    nrfx_spim_xfer_desc_t xfer_desc = NRFX_SPIM_XFER_TX(&cmd_byte, sizeof(cmd_byte));    
    nrfx_spim_xfer(spi_inst, p_xfer_desc, NRFX_SPIM_FLAG_HOLD_XFER);
    task = nrfx_spim_start_task_get(spi_inst);
    nrf_spim_disable(spi_inst->p_reg);
    nrf_gpio_pin_set(RFID_SPI_SCK_PIN);
    nrf_delay_us(1);
    nrf_gpio_pin_set(RFID_SPI_MOSI_PIN);
    nrf_spim_enable(spi_inst->p_reg);
    nrf_spim_task_trigger(spi_inst->p_reg, task);

I tried this with and without the nrf_delay_us call. Initially, the waveform would look fine, like below.

However, by the second or third spim operation the waveform would look like the following, with both MOSI and SCLK going high nearly simultaneously.

This occurred both with and without the nrf_delay_us call between clearing the 2 pins.

Should I be disabling the spim driver again after the transfer and clearing both pins manually, or is something off with my implementation?

RE: Add initialization sequence to SPIM interface

haakonsh — Tue, 02 May 2023 09:13:26 GMT

Try this:

Set up a transfer with the NRFX_SPIM_FLAG_HOLD_XFER flag --> disable(not uninitialize) the SPIM peripheral --> set start conditions manually (CPU toggling of CLK and MOSI pins) --> enable SPIM periheral --> start SPIM transfer.

See the following API docs:

nrfx_spim_xfer
nrf_spim_disable
nrf_spim_enable
nrf_spim_task_trigger(NRF_SPIM_TASK_START)