DMA channel unexpectedly set active

jdupre — Thu, 11 Aug 2016 21:02:11 GMT

I'm following the UART DMA example in LPCOpen for the LPC15xx.

I have a descriptor that looks like this:

/* Descriptor for the channels we need */

dmaRXDesc[0].source = DMA_ADDR(&LPC_USART0->RXDATA);

dmaRXDesc[0].dest = DMA_ADDR(&RxBuf[0] + RX_BUF_SIZE - 1);

dmaRXDesc[0].next = DMA_ADDR(NULL);

dmaRXDesc[0].xfercfg = DMA_XFERCFG_SETINTA

| DMA_XFERCFG_WIDTH_8

| DMA_XFERCFG_SRCINC_0

| DMA_XFERCFG_DSTINC_1

| DMA_XFERCFG_XFERCOUNT(RX_BUF_SIZE);

When I call

Chip_DMA_SetupChannelTransfer(LPC_DMA, DMAREQ_USART0_RX, dmaRXDesc[StartDescIdx].xfercfg);

the active flag for the channel gets set immediately. I don't understand this. If I haven't set DMA_XFERCFG_CFGVALID, shouldn't I have to do something else to make the channel active?

I want to do all the DMA configuration in advance, and then have the UART ISR trigger the pre-configured DMA transfer to start. (I'm monitoring RXBRK and RXDELTABRK in the UART ISR to control when the DMA transfer should start.)

Re: DMA channel unexpectedly set active

Carlos_Mendoza — Wed, 14 Sep 2016 20:31:45 GMT

Hi Joseph,

Apologies for the delay, are you still having problems with the DMA?

Thanks in advance for your response!

Best Regards,
Carlos Mendoza
Technical Support Engineer

topic Re: DMA channel unexpectedly set active in LPC Microcontrollers

DMA channel unexpectedly set active

Re: DMA channel unexpectedly set active