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.)
