下面是一个External Port DMA的例子：

          while((*pDMAC0)&DMAS){asm("nop;");};    // DMA in progress

            *pDMAC0 = 0; //Disable External Port CH 0 DMA
            
            *pIIEP0 = Internal_buffer;   //Internal Memory Source
            *pEIEP0 = SDRAM_wbuffer;  //External Memory Destination
            *pIMEP0 = 1;    //Set up internal modify
            *pEMEP0 = 1;    //Set up external modify
            *pICEP0 = DMA_LEN;  //length of DMA
            *pECEP0 = DMA_LEN;
            
            printf("\nWrite DDR DMA start!\n");

            //Config and enable External Port CH 0 DMA

            *pDMAC0 = DEN|TRAN|DFLSH|INTIRT;    // write to external memory, Internal DMA Completion Interrupt in enabled.

      我参考了你的代码，发现我的程序还有些问题。

     我需要从外部sdram读数据到内部sram，计算好之后再将结果写到外部sdram。我配置了DDR2，我的代码类似于下面的：

DMA_Internal2External(int*Internal_buffer,int *SDRAM_buffer,int DMA_LEN)

{

             while((*pDMAC0)&DMAS){asm("nop;");};  

            *pDMAC0 = 0;      
            *pIIEP0 = Internal_buffer;
            *pEIEP0 = SDRAM_buffer;
            *pIMEP0 = 1;  
            *pEMEP0 = 256;  //此处我设置为256
            *pICEP0 = DMA_LEN;  
            *pECEP0 = DMA_LEN

            *pDMAC0 = DEN|TRAN|DFLSH|INTIRT;

}

DMA_External2Internal(int *SDRAM_rbuffer,int *Internal_buffer,int DMA_LEN)

{

             while((*pDMAC0)&DMAS){asm("nop;")};//代码会在此处死循环，死循环的发生很随机

            *pDMAC0 = 0;      
            *pIIEP0 = Internal_buffer;
            *pEIEP0 = SDRAM_buffer;
            *pIMEP0 = 1;  
            *pEMEP0 = 1;  //此处仍为1
            *pICEP0 = DMA_LEN;  
            *pECEP0 = DMA_LEN

           *pDMAC0 = DEN|DFLSH|INTIRT;

}

调用过程类似于：

for(i = 0; i < 100; i++)

{

     DMA_External2Internal();

     DMA_External2Internal();

     数据计算;

     DMA_Internal2External();

     DMA_Internal2External();

}

我配置了DDR2，不知道是不是这里有问题。

当用DMA将外部数据读入内部时发现，得到的数据里第一个数有时候会读取失败，得到数据0。

另外我用的是adsp-21469评估板

我的问题在哪里呢？谢谢！