• Do you know if those separate 255 byte transfers can be chained such that there isn't a pause in the SPI clock? I guess that might screw up the idea of using it as a general purpose neopixel driver.

    It turns out I was somewhat incorrect on maximum number of bits you can transfer. There is a maximum of 255 bytes per SPI transaction, but, with EasyDMA operating in 'ArrayList' mode, the SPI transaction will be repeated (from the next contiguous address) without a 'pause'. Since the TX and RX is double buffered, presumably this means no pause in the SCK (although I haven't yet tried this). To STOP the transfer, you need to count the TX END events and issue a STOP to the peripheral. This could be done via PPI and a HW counter. This means that, if you can break the data block into 'n' equally sized blocks, then total transfer size is 'n' x TXD.MAXCNT.

    I think the 'ArrayList' terminology is misleading and confusing. It implies (to me anyway) that you can have a list of transactions with independent and dis-contiguous buffers and sizes. Nordic's SPI Manager driver, however DOES provide this, but I doubt that the SPI clock is continuous between transactions. I've used the SPI Manager and it is powerful, but with power comes complexity.


Avatar for TomWS @TomWS started