UART Ring Buffer with DMA using SDK

thosewhowish2b — Fri, 25 Mar 2022 02:01:30 GMT

Hello,

I need to implement a ring buffer for receiving from UART via DMA. For consistency, I'd like to keep using the SDK.

What I want is to set up UART and DMA once, and have a circular buffer that overwrites itself over and over, completely unattended (I can't miss a character, ISR to switch buffer would be too slow). I'll have a periodic task reading from the ring buffer.

The thing is, I just cannot figure out how to do it. The most obvious way I've tried breaks the SDK's abstraction, making it (very) leaky, and also doesn't work:

Looking into edma_driver.h, there is this function EDMA_DRV_ConfigLoopTransfer() which looked to akin to EDMA_DRV_ConfigMultiBlockTransfer() that the UART driver uses. I could find a Freescale document recommending it, but the SDK back there seemed different back then and it tells me to call EDMA_DRV_RequestChannel() beforehand, which is not available anymore: https://www.nxp.com/docs/en/supporting-information/Enhanced-Direct-Memory-Access-Controller-Training.pdf

I tried:

commenting out the parts of the UART driver that stopped the DMA, that just made the DMA write outside the buffer's limit.
making my own function to activate DMA and UART's DMA requests using EDMA_DRV_ConfigLoopTransfer (InitUartDmaReceive()), that leads to DefaultISR on the first char.

So, is there a sensible way to do it? Or is the SDK really just lacking and I have to fiddle with registers?

Attached, a test project of mine. #define DMA_LOOP turns on the looping attempt. Using S32K148EVB-Q176.

Best regards,

Re: UART Ring Buffer with DMA using SDK

lukaszadrapa — Mon, 28 Mar 2022 10:46:20 GMT

Hi Wesley,

the SDK does not cover 100% functionality of the microcontroller. The DMA module itself allows us to handle almost all operations and situations we can think about. However, the UART driver does not cover this use-case. As we do not support modifications of SDK code, this should be implemented rather by your own code.

Regards,

Lukas

topic UART Ring Buffer with DMA using SDK in S32K

UART Ring Buffer with DMA using SDK

Re: UART Ring Buffer with DMA using SDK