Sat, 08 Jul 2000 Andrew Tuckey wrote:
[...]
> What does the actual DMA - the processor or the I/O board? Does there need to
> be some form of processor on the I/O board?
This depends on what bus and architecture is used. The specs I've seen on DSPs
that have DMA support indicate that the asynchronous DMA hardware is on the DSP
chip. It can be used either for memory->memory with maximum speed, or
memory<->I/O port/register, providing the sources and destinations support some
form of handshaking to deal with DMA synchronized to the external hardware.
x86 doesn't have DMA on the chip (*), but uses either the 8 DMA channels on the
mainboard chipset (4 x 8 bit + 4 x 16 bit; normally used with ISA boards) or PCI
busmaster DMA, which is supported by the PCI chipset but performed by the PCI
cards themselves. AGP is quite similar to PCI in this respect, AFAIK.
(*) exception: some x86 clones for embedded systems, with some standard
chipset functionality included.
David Olofson
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