DMA capable devices have more registers than have been used in previous examples. This section adds the following fields to the device register structure to support DMA-capable device examples.
For DMA engines without scatter-gather support:
uint32_t dma_addr; /* starting address for DMA */ uint32_t dma_size; /* amount of data to transfer */
For DMA engines with scatter-gather support:
struct sglentry { uint32_t dma_addr; uint32_t dma_size; } sglist[SGLLEN];
caddr_t iopb_addr; /* When written informs device of the next */ /* command's parameter block address. */ /* When read after an interrupt,contains */ /* the address of the completed command. */