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DMA block transfer not send all bytes

Prakash Balagangatharan
Expert 2440 points
Other Parts Discussed in Thread: MSP430F6438

Hi,

 I am using MSP430F6438.In this i am try send data to uart using DMA. In this case for single transfer DMADT_0 all bytes are sent properly, but if i am using Repeated single transfer DMADT_4 means first time all bytes comes properly, next time bytes are misaligned, and also if i am using block transfer mode DMADT_1 only first byte sent. Can any ome help me.
                DMA2CTL &= ~DMAEN;                
                DMACTL1 = DMA2TSEL_21;
                   
                DMA2CTL |= DMADT_1;   //DMADT_4
             
                DMA2CTL |= DMASRCINCR_3;
                     
                DMA2CTL |= DMASBDB; 
                        
                DMA2SZ = buf_ptr->szBuf;     
                     
                DMA2SA = (uint32_t)buf_ptr->txrxbuf_ptr; 
                     
                DMA2DA = (uint32_t)&uartRegister1->txbuf;
                
                DMA2CTL |= DMAIE;
                  
                DMA2CTL &= ~DMAIFG;  
                      
                DMA2CTL |= DMAEN;             
               
                //uartRegister1->txbuf = *(buf_ptr->txrxbuf_ptr);
               
                uartRegister1->intrflag &= ~(0x02);
                uartRegister1->intrflag |= 0x02;  

 

Thanks in advance

  • 0
    Guru 227245 points

    You should first clear DMAIFG and then set DMAIE, else you might get an interrupt right between the two instructions.

    Block mode means one trigger, many transfers. So when TXIFG gets set, the DMA will stuff szBuf bytes to txbuf as fast as possible (and only the last and maybe – depending on MCLK/baudrate ratio - the first get sent)

    How do you handle the DMA interrupt? Maybe you’re superfluously do a manual trigger there (like the one you did to initially start the transfer). Which would ‘swallow’ one byte.

    The peripherals will (usually) do what you tell them to do, not what you want them to do. J
    You described what you want, but only the code shows what you actually told the peripheral to do.

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