ISA Bus Example

A DMA engine on an ISA bus in an x86 machine has the following attributes:

• Access to the first 16 megabytes of memory only

• Inability to cross a 1-megabyte boundary in a single DMA transfer

• 16-bit counter register

• Ability to handle byte-aligned transfers

• Support for 1-byte, 2-byte, and 4-byte burst sizes

• Minimum effective transfer size of 1 byte

• Ability to hold up to 17 scatter-gather transfers

• Operation on sectors only, for example, a disk

A DMA engine on an ISA bus in an x86 machine has the following attribute structure:

static ddi_dma_attr_t attributes = {
    DMA_ATTR_V0,   /* Version number */
    0x00000000,    /* low address */
    0x00FFFFFF,    /* high address */
    0xFFFF,        /* counter register max */
    1,             /* byte alignment */
    0x7,           /* burst sizes */
    0x1,           /* minimum transfer size */
    0xFFFFFFFF,    /* max transfer size */
    0x000FFFFF,    /* address register max */
    17,            /* scatter-gather */
    512,           /* device operates on sectors */
    0,             /* attr flag: set to 0 */
};