Re: Using PLD or FPGA for ISA bus board with DMA
From: KR Williams (krw_at_att.biz)
Date: 04/25/04
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Date: Sun, 25 Apr 2004 11:28:42 -0400
In article <44b0ca4e.0404242059.3b82c9e8@posting.google.com>,
assaf_sarfati@yahoo.com says...
> <ISA> wrote in message news:<40895aaf$0$20662$afc38c87@news.optusnet.com.au>...
> > I'm planning to build an ADC board with onboard buffer with DMA transfer
> > from onboard buffer to computer's memory.
> > Where can I find an ISA bus board design example with DMA functionality
> > using PLD or FPGA ?
> > What would be the max paractical speed to transfer data from ISA bus to PC's
> > memory?
>
> ISA was never designed for DMA, unless you consider the 8-bit 8237 on the
> motherboard. Both ISA and the 8237 are very much obsolete, and even if
> present on current chipsets, they have probably not been verified for
> correct operation for generations (chip generations, that is).
THere are three forms of ISA DMA. The 8237 DMA registers only
address one. ISA can also busmaster (HOLD/ HOLDA/, IIRC). IBM
had a series of modem/sound cards that did ISA busmastering. It
worked rather well, though the drivers had to copy into buffers
below the 16MB line.
> Unless entirely impossible, I'd suggest designing a PCI board; there are
> many interface chips available, and most of them include some sort of DMA.
> Best of all, the PCI bus was designed to use DMA as its basic data-transfer
> method (it's not called DMA; it's called Master transaction in PCI-speak).
I wouldn't disagree with this assessment. ISA is dead, and may
it stay dead. ;-)
> Designing a board around a PCI interface chip not too bad; the chip makers
> have lots of guides, app notes and possibly even evaluation cards available;
> PCI is doable using 2 signal and 2 power planes - even (if you are very
> careful) only 2 signal planes. OTOH, you can't wire-wrap or protoype one
> very easily.
You won't meet spec without the internal planes. It might work,
but might not. I'd never go below 2S2P for a PCI card, which
throws it out of the range of the hobbyist.
>
> If going the PCI route, I'd recommend learning at least the PCI basics,
> since it's very different from ISA, or any single-processor async bus
> (which ISA basically is).
-- Keith
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