Complex SPI transactions with PPI compatible with Zephyr?

RE: Complex SPI transactions with PPI compatible with Zephyr?

Vidar Berg — Mon, 14 Mar 2022 09:42:19 GMT

That is good news. Thank you for the update.

RE: Complex SPI transactions with PPI compatible with Zephyr?

Kyrre Aalerud — Mon, 14 Mar 2022 08:49:57 GMT

You are correct, this can be done in a single operation with 1 dummy byte in receive buffer and 1 byte length set in tx_length. It was a mistake on my part assuming the CS needed deasserting between the transfers. This is true for the memory chip but not the sensor that we are using and where we want to optimize. It is thus possible with a single transaction.

RE: Complex SPI transactions with PPI compatible with Zephyr?

Vidar Berg — Mon, 14 Mar 2022 08:27:32 GMT

[quote user=""]an address to the external device from the first tx buffer in the set, while ignoring the reception, having a NULL rx buffer before going on to the second set of buffers where the tx buffer is NULL and rx buffer is now valid and a count tells it to receive a set of data values.[/quote]

What is the reason you can't set this up as a single transfer? Is it because you don't want to waste RX and TX buffers, or is it because you need to de-assert the CS line between these 2 transactions?

RE: Complex SPI transactions with PPI compatible with Zephyr?

Kyrre Aalerud — Mon, 14 Mar 2022 07:15:27 GMT

This is exactly what I am describing, but it handles a single transfer only. The complex function of multiple tx and rx buffers and events to handle a potential setup or address in external unit is handled by the spi library and interrupt handler and as such is incapable of handling this via ppi and not involving the cpu.

RE: Complex SPI transactions with PPI compatible with Zephyr?

Vidar Berg — Fri, 11 Mar 2022 16:38:48 GMT

Hello,

For the scenario you outline you will likely need to work work with the nrfx driver APIs directly. There you have the nrfx_spim_xfer() function which lets you set up repeated TXRX transfers with auto increment of the RX and TX pointer (easyDMA list feature) and optionally with the END interrupt disabled (NRFX_SPIM_FLAG_NO_XFER_EVT_HANDLER).

Note that when using the NRFX_SPIM_FLAG_NO_XFER_EVT_HANDLER flag, you can connect the END event via PPI to a TIMER in counter mode to keep track how many transfers have been completed.

The Zephyr nrfx use example demonstrates how you can use nrfx drivers in the SDK.

Best regards,

Vidar