想利用dma抓两幅图像到内存，

单幅图像通过单次DMA实现了；所以EPPI及基本的DMA配置应该是正确的。

现在，想利用描述符的DMA传输2幅图像时，寄存器配置如下；结果，内存中一副图像也没有。

VideoInDMAList[0].pStartAddress = ADV7280VideoBuffer;
VideoInDMAList[0].XCount = IMAGE_WIDTH / 2;
VideoInDMAList[0].XModify = 0x4;
VideoInDMAList[0].YCount = IMAGE_HEIGHT;
VideoInDMAList[0].YModify = 0x4;
VideoInDMAList[0].Config = ENUM_DMA_CFG_WRITE |
                                            ENUM_DMA_CFG_MSIZE04 |
                                            ENUM_DMA_CFG_PSIZE04 |
                                            ENUM_DMA_CFG_ADDR2D |
                                            ENUM_DMA_CFG_SYNC |
                                            ENUM_DMA_CFG_DSCLIST |
                                            ENUM_DMA_CFG_EN;
VideoInDMAList[0].pNext = &VideoInDMAList[0];
VideoInDMAList[0].bCallbackWhenDone = false;

VideoInDMAList[1].pStartAddress = ADV7280VideoBuffer1;
VideoInDMAList[1].XCount = IMAGE_WIDTH / 2;
VideoInDMAList[1].XModify = 0x4;
VideoInDMAList[1].YCount = IMAGE_HEIGHT;
VideoInDMAList[1].YModify = 0x4;
VideoInDMAList[1].Config = ENUM_DMA_CFG_WRITE |
                                            ENUM_DMA_CFG_MSIZE04 |
                                            ENUM_DMA_CFG_PSIZE04 |
                                            ENUM_DMA_CFG_ADDR2D |
                                            ENUM_DMA_CFG_SYNC |
                                            ENUM_DMA_CFG_STOP |
                                            ENUM_DMA_CFG_EN;
VideoInDMAList[1].pNext = &VideoInDMAList[0];
VideoInDMAList[1].bCallbackWhenDone = false;

*pREG_DMA33_DSCPTR_NXT = &VideoInDMAList[0];
ssync();
*pREG_DMA33_CFG = ENUM_DMA_CFG_READ |        //看编程手册说，第一次要设成read，尝试设成write也不行
                                     ENUM_DMA_CFG_MSIZE04 |
                                     ENUM_DMA_CFG_PSIZE04 |
                                     ENUM_DMA_CFG_ADDR2D |
                                     ENUM_DMA_CFG_SYNC |
                                     ENUM_DMA_CFG_DSCLIST |
                                     ENUM_DMA_CFG_FETCH02;
ssync();

最后，使能DMA33

这个也有试过，描述符0 dma配置成ENUM_DMA_CFG_STOP，也是没图像；所以，不知道触发描述符DMA的流程是否正确

VideoInDMAList[0].Config = ENUM_DMA_CFG_WRITE |
                                            ENUM_DMA_CFG_MSIZE04 |
                                            ENUM_DMA_CFG_PSIZE04 |
                                            ENUM_DMA_CFG_ADDR2D |
                                            ENUM_DMA_CFG_SYNC |
                                            ENUM_DMA_CFG_STOP  |
                                            ENUM_DMA_CFG_EN;