SPI not transferring when sck pin not used

RE: SPI not transferring when sck pin not used

JVKran — Wed, 21 Oct 2020 14:52:09 GMT

Haven't looked at it that way. Thanks. This was my first question by the way. Still a bit new all this ; ).

RE: SPI not transferring when sck pin not used

awneil — Wed, 21 Oct 2020 14:34:25 GMT

Well, the question of why it happens is answered - so marking it would help people to find threads which answer the question?

RE: SPI not transferring when sck pin not used

JVKran — Wed, 21 Oct 2020 14:26:23 GMT

Is it solved though? It is temporarily solved with a workaround. Wouldn't be too hard for the devs to implement a construction that throws an error when sck_pin is set to not_used. Could save people a lot of time...

RE: SPI not transferring when sck pin not used

awneil — Wed, 21 Oct 2020 11:27:26 GMT

[quote userid="94539" url="~/f/nordic-q-a/67405/spi-not-transferring-when-sck-pin-not-used/276084#276084"]Just wish it would've been easier to find[/quote]

I guess that always the trouble with "abusing" a feature like this.

😞

Still interesting that you got away with it on the nRF52832, though!

RE: SPI not transferring when sck pin not used

JVKran — Wed, 21 Oct 2020 07:35:20 GMT

Oh well... That's great... Makes sense though. Just wish it would've been easier to find or using the macro on the sck_pin threw an error.

RE: SPI not transferring when sck pin not used

hmolesworth — Tue, 20 Oct 2020 22:53:51 GMT

We found that the general purpose peripheral which underlies SPIM/TWIM requires the clock signal to physically exist otherwise the internal registers are not clocked; maybe a consequence of using the same peripheral hardware to accept both internal (master) and external (slave) synchronous clock to drive the registers. Somewhere there is a note about this, but of course I don't remember where. This only applies to SCK, not MOSI and MISO. It's not bug, it's a feature ..

RE: SPI not transferring when sck pin not used

JVKran — Tue, 20 Oct 2020 11:09:56 GMT

Yes, I've looked at it but couldn't find anything obvious. In fact, the NRF_DRV_SPI_DEFAULT_CONFIG even has all pins (sck, mosi, miso and ss) set to NRF_DRV_SPI_PIN_NOT_USED.

RE: SPI not transferring when sck pin not used

awneil — Tue, 20 Oct 2020 11:03:11 GMT

Have you tried looking at (or stepping through) the code to see if there's anything obvious that's messed up by having the SCK pin as 'Not Used' ... ?

RE: SPI not transferring when sck pin not used

JVKran — Tue, 20 Oct 2020 10:45:51 GMT

Yep, haha. I know it's kinda mis-using SPI, but still; I wouldn't expect the macro to completely prevent transactions from completing.

At least there's a temporary fix; wouldn't be the end of the world if there isn't a proper solution.

RE: SPI not transferring when sck pin not used

awneil — Tue, 20 Oct 2020 10:18:17 GMT

Aha - that's a key bit of information! Yes, I have done this on nRF52832; haven't tried nRF52840.

Strictly, it is using the SPI peripheral in a way it's not intended - I guess we'll have to wait for the Nordic guys to say if there's anything that can be done ...

RE: SPI not transferring when sck pin not used

JVKran — Tue, 20 Oct 2020 10:01:02 GMT

Sorry, forgot to add that I wrote a library for the WS2812 leds. Using SPI at 4MHz with DMA is a very efficient way to control these leds. Then, 4 bits represent 1 bit in the WS2812 protocol. Hence MOSI is connected straight to the DIN pin of the leds and other pins are not used nor necessary.

RE: SPI not transferring when sck pin not used

awneil — Tue, 20 Oct 2020 09:57:23 GMT

Why would you set the SCK pin as 'not used' - surely that makes no sense?!

SCK is essential to SPI.