Receiving SPI data via DMA on PIC32

Question

I know that this topic (DMA & SPI) has already been talked about on numerous threads in the microchip forum, actually i've read all the 15 pages in result of the search with keyword "dma" and read all the topics about dma & spi.

And I am still stuck with my problem I hope someone can help me :)

Here is the problem.

My chip is a PIC32MX775F512H. I am trying to receive (only receive) data using SPI via DMA. Since you cannot "just" receive in SPI, and that the SPI core starts toggling the SPI clock only if you write into the SPIBUF (SPI1ABUF for me) I am trying to receive my data using 2 DMA channels. DMA_CHANNEL1 for the transmitting part. DMA_CHANNEL2 for the receiving part.

I copy pasted the code from http://www.microchip.com/forums/tm.aspx?tree=true&high=&m=562453&mpage=1#

And tried to make it work without any luck. It only receives several bytes (5 or 6).

I've set the Event Enable Flags to DMA_EV_BLOCK_DONE for both dma channels, no interrupt occurs.

Do you have any idea ?

Here is the code I am using :

int Spi_recv_via_DMA(SPI_simple_master_class* SPI_Port, int8u *in_bytes, int16u num_bytes2) 
{ 
DmaChannel   dmaTxChn=DMA_CHANNEL1; 
DmaChannel   dmaRxChn=DMA_CHANNEL2; 
SpiChannel   spiTxChn=SPI_Port->channel; 
    int8u           dummy_input; 

    DmaChnOpen(dmaTxChn, DMA_CHN_PRI3, DMA_OPEN_DEFAULT); 
    DmaChnOpen(dmaRxChn, DMA_CHN_PRI3, DMA_OPEN_DEFAULT); 

    DmaChnSetEventControl(dmaTxChn, DMA_EV_START_IRQ_EN | DMA_EV_START_IRQ(_SPI1A_RX_IRQ)); 
    DmaChnSetEventControl(dmaRxChn, DMA_EV_START_IRQ_EN | DMA_EV_START_IRQ(_SPI1A_RX_IRQ)); 

    DmaChnClrEvFlags(dmaTxChn, DMA_EV_ALL_EVNTS); 
    DmaChnClrEvFlags(dmaRxChn, DMA_EV_ALL_EVNTS); 
    DmaChnSetEvEnableFlags(dmaRxChn, DMA_EV_BLOCK_DONE); 
    DmaChnSetEvEnableFlags(dmaTxChn, DMA_EV_BLOCK_DONE); 

    //SpiChnClrTxIntFlag(spiTxChn); 
    //SpiChnClrRxIntFlag(spiTxChn); 

    DmaChnSetTxfer(dmaTxChn, tx_dummy_buffer, (void *)&SPI1ABUF, num_bytes2, 1, 1); 
    DmaChnSetTxfer(dmaRxChn, (void *)&SPI1ABUF, in_bytes, 1, num_bytes2, 1); 

    while ( (SPI1ASTAT & SPIRBE) == 0) 
        dummy_input = SPI1ABUF; 
    SPI1ASTAT &= ~SPIROV; 

    DmaRxIntFlag = 0; 
    DmaChnEnable(dmaRxChn); 
    DmaChnStartTxfer(dmaTxChn, DMA_WAIT_NOT, 0); 


    while(!DmaRxIntFlag); 
    return 1;    
}

with those two interrupt handlers :

// handler for the DMA channel 1 interrupt 
void __ISR(_DMA1_VECTOR, ipl5) DmaHandler1(void) 
{ 
int evFlags;     // event flags when getting the interrupt 
    //LED_On(LED_CFG); 
INTClearFlag(INT_SOURCE_DMA(DMA_CHANNEL1)); // acknowledge the INT controller, we're servicing int 

evFlags=DmaChnGetEvFlags(DMA_CHANNEL1); // get the event flags 

    if(evFlags&DMA_EV_BLOCK_DONE) 
    { // just a sanity check. we enabled just the DMA_EV_BLOCK_DONE transfer done interrupt 
        DmaTxIntFlag = 1; 
    DmaChnClrEvFlags(DMA_CHANNEL1, DMA_EV_BLOCK_DONE); 
    } 
   // LED_Off(LED_CFG); 
} 

void __ISR(_DMA2_VECTOR, ipl5) DmaHandler2(void) 
{ 
int evFlags;     // event flags when getting the interrupt 

INTClearFlag(INT_SOURCE_DMA(DMA_CHANNEL2)); // acknowledge the INT controller, we're servicing int 

evFlags=DmaChnGetEvFlags(DMA_CHANNEL2); // get the event flags 

    if(evFlags&DMA_EV_BLOCK_DONE) 
    { // just a sanity check. we enabled just the DMA_EV_BLOCK_DONE transfer done interrupt 
        DmaRxIntFlag = 1; 
    DmaChnClrEvFlags(DMA_CHANNEL2, DMA_EV_BLOCK_DONE); 
    } 
}

So I end up waiting forever at the line : while(!DmaRxIntFlag);

I have put breakpoints in the interrupt vectors, they are never called.

This is the state of several registers during the ever lasting wait :

DMACON 0x0000C800
DMASTAT 0x00000001

I am using SPI1A port, so SPI1ABUF and _SPI1A_RX_IRQ

DCH1SPTR 0x5
DCH1SSIZ 0x2B

DCH2DPTR 0x6
DCH2DSIZ 0x2B

DCH2CON 0x00008083
DCH2ECON 0x1B10
DCH2INT 0x00800C4
DCH2SSA 0x1F805820
DCH2DSA 0x00000620

Channel 1 is used to transmit
Channel 2 is used to receive

What kind of device is on the other end of the SPI connection? I'd have to assume it is already in a mode where it is sending data? — Jon L

Alberto Alberto · Accepted Answer · 2013-04-30T15:21:51

You are missing these:

INTEnable(INT_SOURCE_DMA(dmaTxChn), INT_ENABLED);   // Tx
INTEnable(INT_SOURCE_DMA(dmaRxChn), INT_ENABLED);   // Rx

rigth before

DmaRxIntFlag = 0; 
DmaChnEnable(dmaRxChn); 
DmaChnStartTxfer(dmaTxChn, DMA_WAIT_NOT, 0);

Good luck!

Receiving SPI data via DMA on PIC32

2 Answers