LPC Microcontrollers中的主题 Re: LCP54S018M DMA driver questions

LCP54S018M DMA driver questions

carson_cummins — Wed, 16 Sep 2020 17:52:54 GMT

Hello all,

I'm a developer implementing DMA to transfer transmit only data (no recieve) to multiple flexcomm ports. I have a few questions:

1. I'm using the latest 2.8.0 SDK with DMA driver files included (fsl_dma & fsl_spi_dma .c/.h). There is no definition for FSL_FEATURE_DMA_DESCRIPTOR_ALIGN_SIZE. Can someone point me in the right direction as to what this should be?

2. There is no definition that matches the description of the DMA_ALLOCATE_LINK_DESCRIPTOR(nextDesc) macro as discussed on line 866 -881 in fsl_dma.c. I see a definition of DMA_ALLOCATE_LINK_DESCRIPTORS (with an 'S') but it appears to function differently than described in the comment.

3. I'm encountering an issue with linked list DMA to SPI peripheral transfers. On every flexcomm channel I've set up, there is an intermittent extra bit inserted in to the data stream that is shifting the data going out by one. I'm interfacing with WS2812B LEDs and this is causing them to flicker. The data being transferred has been verified as correct so I'm not sure where this extra bit is coming from.

Thank you in advance.

Re: LCP54S018M DMA driver questions

Alice_Yang — Thu, 17 Sep 2020 07:55:36 GMT

Hello carson_summins,

I recommend you open the SDK demo "dma_linked_transfer", you can find the

description of your two question.

1. " FSL_FEATURE_DMA_DESCRIPTOR_ALIGN_SIZE"

2. "DMA_ALLOCATE_LINK_DESCRIPTOR" is one of DMA descriptor of "DMA_ALLOCATE_LINK_DESCRIPTORS".

Re: LCP54S018M DMA driver questions

carson_cummins — Tue, 22 Sep 2020 18:12:50 GMT

Re: LCP54S018M DMA driver questions

carson_cummins — Tue, 22 Sep 2020 18:14:26 GMT

Wonderful, thank you. Is there anything you can infer from #3? I've looked at the code examples provided by NXP and they don't really cover an instance where DMA is being used without needing RX. I've got the setup somewhat functional sending data only DMA->SPI but I don't think the provided driver file was designed with ignoring RX data in mind. Do you or anyone else know of any example code that I could view?

Re: LCP54S018M DMA driver questions

Alice_Yang — Thu, 24 Sep 2020 02:48:29 GMT

Hello carson_cummins,

Recommend you using logic analyzer check transfer signal.