>
> 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.
Is it possible to run the DMA to/from the I/O board at a different speed
(back-plane - 5 wait states) to the main memory (on the main PCB - no wait
states)? (It _is_ possible that this is the whole idea of DMA!) Is there bus
arbitration problems/bottle-necks?
> 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.
Is the PCI bus DMA much faster than the ISA bus DMA (i.e. 32-bit data bus,
higher speed)?
--
Andrew Tuckey, Visiting Lecturer
Electrical and Computer Engineering Department
University of Wisconsin - Madison
1415 Engineering Drive
Madison, WI 53706-1691
Email: [EMAIL PROTECTED]
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