Hello,
I have been working with the CC2530 and need to know how to use the DMA for both sending and receiving using USART0 in SPI master mode. I have been looking through various application notes and found DN112 and DN113 quite helpful. However, I am unsure that I understand how to both send and receive at the same time. From my reading I have produced the DMA_VECTOR interrupt code shown below. I would like to know if this code reflects a correct understanding of DMA operation with SPI (I cannot test at the moment) assuming that DMA channels 0 and 1 and the buffers have been properly setup elsewhere.
If the DMA interrupt is either from channel 0 (for SPI Tx) or from channel 1 (for SPI Rx), I wait until USART0 is inactive. Will both TX and RX be finished at this point?
Then I clear both interrupt flags. At this point, will both interrupt flags be high? Do I need to clear IRCON again? How would this affect DMA channels 2-4 if I need to use them as well?
Finally, I deselect the SPI slave, reset the buffers, arm the channels, and reselect the slave. Then I trigger the first transmission, but I don't completely understand why I have to do that.
I also thought about treating the two channels in different if blocks, but I thought that might cause a double interrupt if transmit and receive do not finish at the same time. I think that could cause problems if the transmit channel was used as an interrupt before the receive channel was serviced.
#pragma vector=DMA_VECTOR __interrupt void dma_ISR(void)
{
//Clear DMA CPU interrupt flag
IRCON&=~0x01;
//Determine interrupting DMA channel (0 or 1 or both)
if(DMAIRQ & 0x03)
{
//Wait for transfer to complete
while(U0ACTIVE);
//Clear DMA channel 0 and 1 interrupt flags
DMAIRQ&=~0x03;
//Set slave select high
CS=1;
//Reset SPI transmit buffer
SPI_TX_IND=0;
//Reset SPI recieve buffer
SPI_RX_IND=0;
//Arm DMA channel 0 and 1
DMAARM|=0x03;
//Set slave select low
CS=0;
//Trigger first transmission
U0DBUF=SPI_TX_BUF[SPI_TX_IND++];
//First reception occurs automatically?
}
}
I would appreciate clarification of these questions. Thank you in advance for your help.
