S32KのトピックCircular buffer - DMA transfer

Circular buffer - DMA transfer

user_244572 — Wed, 29 Jan 2025 12:12:49 GMT

Hello NXP team,

Is there a way to configure DMA for a circular buffer transfer other than the source and destination modulo variable ?
what if the buffer size is not a power of 2 ?

example array size is 10, number of bytes to be transfered is 10 x 2 = 20 bytes ?

Thanks,

Re: Circular buffer - DMA transfer

davidtosenovjan — Wed, 29 Jan 2025 17:25:19 GMT

It is indeed the most common configuration.

Double buffering scheme you may also create with using of INT_HALF interrupt.

But you may use links or scatter/gather features to create special configuration just in accordance to your specific needs.

Re: Circular buffer - DMA transfer

user_244572 — Thu, 30 Jan 2025 07:51:41 GMT

Hi David,

Thanks for your answer.

Can you elaborate more on that ?

what if the buffer size changes dynamically as well ?

It would be great if you can provide examples.

My ultimate goal at the end is to read data periodically from a lookup table that changes dynamically in sizes based on input frequency and transfer this data to Emios registers.
We need to read from the table in a circular way.

Thanks,

Re: Circular buffer - DMA transfer

davidtosenovjan — Mon, 03 Feb 2025 12:52:04 GMT

Here you may see appnote dealing with eDMA (even written for different product line, it is still almost the same DMA module
https://www.nxp.com/docs/en/application-note/AN4765.pdf

Witch Scatter-gather functionality you may achieve even dynamic buffer size, even it may be mor complex use.

In RM, there is a chapter dealing with this in a great detail:
15.5.8 Dynamic programming