RE: Updating SPI transfer with PPI

Einar Thorsrud — Tue, 21 May 2019 09:13:00 GMT

Hi,

I am not sure this will solve the issue you have. Is the time when you need to toggle between values constant, or does it depend on something else? If it is constant then it should be OK to use fixed length transfers and start the next transfer after the previous has finished via PPI (for instance by a timer like you do). However, the array list is not circular, so you will have to start again via SW when you have iterated through your array list.

There is no example in the SDK that demonstrates EasyDMA array list, but the driver documentation covers this under Repeated transfers. Essentially you set up an array of transfers, and when you start a new transfer, this increases the array index list so that the next data array is used.

I have not tested your code, but it looks like you have the main parts you need. However, I notice the following

You use NRF_DRV_SPI_FLAG_RX_POSTINC, but it should be NRF_DRV_SPI_FLAG_TX_POSTINC, which is probably what you want?
Do you care about RX data? If you can use NRF_DRV_SPI_XFER_TX, or just set the third parameter in NRF_DRV_SPI_XFER_TRX to null.

If you go this route and have problems after testing it, can you provide updated code and a description of the problems you are seeing?