基于NiosII的DMA传输总结.doc

最近练了一段时间的DMA传输，现做如下的总结，分享自己获得心得以及遇到的一些问题。 在系统运行时，当需要传输大量数据时，可以采用DMA的方式进行传输，以解脱出CPU来处理其他命令。Nios II中的DMA传输有以下三种形式：1、 存储器到存储器这种情况下需要同时打开发送通道和接收通道，而且源地址和目标地址都是自增的。tx = alt_dma_txchan_open(/dev/dma_0);/打开发送通道dma_res = alt_dma_txchan_send(tx, tx_buf, 32, NULL, NULL); / tx_buf是源地址rx = alt_dma_rxchan_open(/dev/dma_0);/打开接收通道dma_res = alt_dma_rxchan_prepare(rx, rx_buf, 32, dma_done, NULL); / rx_buf是目标地址，dma_done()是DMA完成后被调用的回调函数。2、 存储器到外设这种情况下只要打开发送通道，而且源地址是自增的，目标地址是固定的。tx = alt_dma_txchan_open(/dev/dma_0); / 打开发送通道alt_dma_txchan_ioctl(tx, ALT_DMA_TX_ONLY_ON, (void *)dst_addr); / dst_addr是目标地址dma_res = alt_dma_txchan_send(tx, tx_buf, 32, dma_done, NULL); / tx_buf是源地址3、 外设到存储器这种情况下只要打开接收通道，而且源地址是固定的，目标地址是自增的。rx = alt_dma_rxchan_open(/dev/dma_0); / 打开接收通道alt_dma_rxchan_ioctl(rx, ALT_DMA_RX_ONLY_ON, (void *)source_addr); / source_addr是源地址dma_res = alt_dma_rxchan_prepare(rx, rx_buf, 32, dma_done, NULL); / rx_buf是目标地址其中通过alt_dma_txchan_ioctl，alt_dma_rxchan_ioctl还可以设置每次发送和接收的字节数。下面给出两个实例，说明DMA传输的过程。1、 存储器到存储器下面程序为SDRAM到onchip-memory的数据传输。硬件连接图示：程序如下：#include #include #include #include system.hstatic volatile int rx_done = 0;int rc;alt_dma_txchan txchan;alt_dma_rxchan rxchan;static char buff256;void* tx_data = (void*) buff; /* 源地址 */void* rx_buffer = (void*) 0x01801000; /* 目标地址，从上图看到0x01801000为onchip-memory的地址*/DMA传输结束回调函数static void done_t(void* handle, void* data) rx_done+; int main (int argc, char* argv, char* envp)/* 打开发送通道 */if (txchan = alt_dma_txchan_open(/dev/dma) = NULL) printf (Failed to open transmit channeln); exit (1);/* 打开接收通道 */if (rxchan = alt_dma_rxchan_open(/dev/dma) = NULL) printf (Failed to open receive channeln); exit (1);/* 开始发送数据 */if (rc = alt_dma_txchan_send (txchan, tx_data, 128, NULL, NULL) 0) printf (Failed to post transmit request, reason = %in, rc); exit (1);/* 开始接收数据*/if (rc = alt_dma_rxchan_prepare (rxchan, rx_buffer, 128, done_t, NULL) 0) printf (Failed to post read request, reason = %in, rc); exit (1);/* 等待传输结束 */while (!rx_done);printf (Transfer successful!n);return 0;程序运行结束后在Nios IDE的console界面中显示：Transfer successful!表明传输成功。2、 存储器到UART下面程序为SDRAM到UART的数据传输硬件连接图：程序如下：#include #include #include sys/alt_dma.h#include altera_avalon_uart_regs.h#include system.h#include alt_types.hstatic volatile int tx_done = 0;volatile static alt_u8 chr20 = 1,2,3,4,6,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20 ;/待发送的数据/回调函数static void done (void* handle)tx_done+;int main()int rc;alt_dma_txchan txchan;void* source_buff_ptr = (void*) chr; /* 源地址 */void* destination_buff_ptr = (void*)IOADDR_ALTERA_AVALON_UART_TXDATA(UART_BASE); /* 目标地址IOADDR_ALTERA_AVALON_UART_TXDATA(UART_BASE)函数读出txdata的地址 */* 打开发送通道 */if (txchan = alt_dma_txchan_open(/dev/dma) = NULL)printf (Failed to open transmit channeln);exit (1);/* 设置目标地址固定 */if (rc = alt_dma_txchan_ioctl(txchan, ALT_DMA_TX_ONLY_ON, destination_buff_ptr) 0)printf (Failed to set ioctl, reason = %in, rc);exit (1);/设置每次发送一个字节，即8位，因为UART每次只发送8位if(rc = alt_dma_txchan_ioctl(txchan,ALT_DMA_SET_MODE_8 ,NULL)0) printf(Failed to set mode 8n); exit(1);/* 开始发送 */if (rc = alt_dma_txchan_send(txchan, source_buff_ptr, 20, done, NULL) 0)printf (Failed to post transmit request, reason = %