Change PPI Controlled SPI Message?

[Fan Jiaming]

Hi,

I am currently implementing an application which uses PPI to control SPI transaction when a HIGH-LOW transition is detected on a GPIO pin.

I first set up the transaction using nrf_drv_spi_xfer with RAM TX and RX buffer, also with the NRF_DRV_SPI_FLAG_HOLD_XFER flag. The program runs without problem.

I wonder if it is possible to change the content of what I send in between the PPI triggered transaction. For example I would like to send a 0x41 instead of 0x4B in the next transaction.

I have tried changing the RAM buffer content in the SPI event handler after each transaction, but it doesn't seems to work. I tried to set up nrf_drv_spi_xfer again that points to differnt buffer and reconnect it to PPI, but it also doesn't do the trick.

Is there a way?

[Petter Myhre]

Sounds like you want to use repeated transfers with the NRF_DRV_SPI_FLAG_TX_POSTINC flag. Have you looked into that?

[Fan Jiaming]

Oh, it didn't occur to me I could implement this function using that flag. Should I also include the repeated transfer flag, as I am not sure about what repeated transfer does? Will the transaction keeps going on without PPI triggering a new task until you stop the transaction explicitly in the SPI handler?

[Fan Jiaming]

Also, do you have any idea why changing the buffer content in the SPI handler doesn't work?

[Petter Myhre]

That I don't know. If you want to share a complete project that reproduces the behavior I can try to test it here.

[Petter Myhre]

And yes you should use repeated transfer. Each transaction should still be triggered by PPI. See the Repeated transfers section here.