With the ISA, it depends on the TYPE of DMA you use. If you use one of the
channels on the motherboard, there sould be no problem. It's only a bit
shaky if you try to run it from the bus itself. That's because of
motherboard features. Since there's to be no motherboard, i.e. only a
passive ISA backplane, that shouldn't be a limitation. It's not necessary,
in general, to have DMA, first because the processors used on PC
motherboards have block transfer operations which operate at the bus
bandwidth.
The only things which would be inherited from the adoption of ISA as an open
bus would be the connector and the signal definitions. I see nothing wrong
with those. One could even punt the 14.318 MHz (4x color-burst) oscillator
in favor of a more useful one, or perhaps none at all.
The types of boards useful in development don't need a lot of documentation
to be used outside the MSDOS/PC world. The base locations of the 8250's on
I/O boards is know, the base of the printer port (twisted though it is) is
known, and one doesn't need a video board right off the top. The WD1003-WAH
board is well uderstood and the EIDE interface emulates that pretty well.
That solves the mass storage problems. Serial I/O is straigtforward enough.
Where's the problem?
Dick
-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Saturday, July 03, 1999 3:24 PM
Subject: Re: OT: A call to arms (sort of)
>>
>> Well . . . what could possibly be more "open" than the ISA. It's capable
of
>> pretty much anything that the PDP-11 could dish out, AND you can get paid
>
>Well, apart from interupt sharing, multiple bus masters (the 16 bit ISA
>allows for _one_ bus master card, but it doesn't really handle it
>properly), certain DMA transfers, etc, etc, etc...
>
>> for taking the boards away from a lot of places. Almost any function you
>
>But most of these cards are _NOT_ 'open'. Try getting complete
>programmings specs for certain video cards, let alone schematics, PAL
>equations, etc.
>
>The whole idea of this is to make an open PC, _because_ existing cards
>are not fully documented.
>
>-tony
>
Received on Sat Jul 03 1999 - 17:22:11 BST