SPIM with DMA Problem?

RE: SPIM with DMA Problem?

haakonsh — Tue, 18 Jan 2022 17:30:20 GMT

Hey Helmet,

That API call is most likely non-blocking and that ~2ms delay is the time it takes to transfer your data. If you used the API as intended then you can use that ~2ms for something useful.

BR,
Håko Holdhus

RE: SPIM with DMA Problem?

HelmetWithHornInstalledInside — Tue, 18 Jan 2022 15:25:37 GMT

Hello Haakonsh, I have found the problem.

I believe the status (most likely) register would trigger SPI's library read+write function to return the result once data is detected on the SPI bus, even though the data hasn't been updated to the designated buffer area.

This is particularly noticeable when the transmission speed is 125K.

I put a 2ms (yes, that much) delay in the function and it fixed the problem.

So basically, after that library function returned, I wait for 2ms for the data to "actually" be updated to the buffer in the memory.

Cheers.

RE: SPIM with DMA Problem?

haakonsh — Thu, 13 Jan 2022 08:01:30 GMT

I suggest you share the relevant code, then I can see what's going on. If you're not using an event handler and the transfer function is non-blocking, then you will most likely get the kind of issue that you're observing.

RE: SPIM with DMA Problem?

HelmetWithHornInstalledInside — Thu, 13 Jan 2022 07:45:22 GMT

I built everything based on the SPIM example from the Nordic SDK (version 17? or so) downloaded from NordSemi official site.

That said, I pull data from SPI using on of the example function with a pointer pointing to the receiving buffer as parameter passed in.

I didn't care much for callbacks/handlers. Is it possible that you can only successfully update rx data with a handler? That would be a rather strange design.

RE: SPIM with DMA Problem?

haakonsh — Wed, 12 Jan 2022 11:39:48 GMT

Well, the most common method for data transfers in drivers for DMA peripherals is a non-blocking transfer function and a event handler that notifies the application when a transfer is completed. How do you handle the SPIM events?