RE: How to properly configure periodic SPI transfers with PPI and TIMER?

user14926 — Wed, 15 Jun 2022 13:28:09 GMT

Hi,

The second argument to nrfx_timer_compare_event_address_get() should be the TIMER COMPARE channel, not the PPI channel (e.g. 0 for COMPARE0). Most likely, the variable readingEventAddr does not contain the desired address after the function call (0x40008140), and the PPI channel will connect to something else.

[quote user=""]1) Here it describes that if I wanto to use the NRFX_SPIM_FLAG_HOLD_XFER flag I must to set the chip select pin as NRFX_SPIM_PIN_NOT_USED and manage it outside the driver. How I should do it if the tranfers are supposed to be autonomous?[/quote]

If you have multiple SPI devices on the same bus, or need to control the CS line for power reasons, you can setup multiple COMPARE events to trigger after each other in the same timer, and use a second PPI channel together with GPIOTE to toggle the CS line before starting the SPI transfer. Similarly, you can toggle the GPIOTE channel when SPI END event is generated.

[quote user=""]2) To generate the TIMER0 event in the PPI can I set false the enable_int parameter in the nrfx_timer_compare function or I have to set it as true? Because if I enable the interrupt, the Zephyr OS crash and restart the chip.[/quote]

Yes, interrupt is not needed when using PPI. This is only used when you need the event to trigger an interrupt in SW.

Best regards,
Jørgen