Xref: utzoo comp.sys.mac.hardware:420 comp.sys.mac.programmer:10435
Path: utzoo!attcan!sobmips!uunet!cs.utexas.edu!usc!jarthur!bridge2!apple!apple.com!chewy
From: chewy@apple.com (Paul Snively)
Newsgroups: comp.sys.mac.hardware,comp.sys.mac.programmer
Subject: Re: Mac "Accelerators" and "DMA"
Message-ID: <5220@internal.Apple.COM>
Date: 16 Nov 89 17:25:13 GMT
References: <1989Nov15.214527.1212@jose.uucp>
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 38

In article <1989Nov15.214527.1212@jose.uucp> ken@jose.uucp (Ken MacLeod) 
writes:
>   Why isn't there an accelerator that is _just_ a processor and memory
> on a card, and passes I/O commands (at quickdraw, file manager, etc. 
levels)
> on to the motherboard?  For bulk transfers, the motherboard can either
> read/write directly into the card's memory instruction at a time, or the
> card can include a simple memory-to-memory DMA that the motherboard CPU
> sets up.  For control structures, two CPU RAM regions would be logically
> mapped so that pointers could point to one from the other.  The M-to-M
> DMA unit could also be used for reads/writes into video card RAM (if you
> know how QuickDraw or PostScript handles rasterizing, you should drop
> your jaw in awe of what that means, CPU handles start/end, DMA handles
> between while CPU...).
> 
>   It seems to me that the CPU/NuBus technology is already there, and from
> enough programming on the Mac it seems simple enough to copy the ROMs 
into
> the card and patch in interfaces that send the relevant commands to the
> motherboard, and let the ROMs on the motherboard take it from there.

Uh... I honestly don't believe you could possibly have looked at much of 
our ROM code and still be saying that with a straight face. :-)

I'm not the hardware guru here, though, so let me pass it on to them to 
comment on...

At least one DMA SCSI card has been done, but certainly nothing of the 
scope that you're suggesting.  It's a great idea, but I think it'd take 
pretty much a total rewrite of everything that we have.  Not that that'd a 
bad idea; it's just expensive.

__________________________________________________________________________
Just because I work for Apple Computer, Inc. doesn't mean that they 
believe what I believe or vice-versa.
__________________________________________________________________________
C++ -- The language in which only friends can access your private members.
__________________________________________________________________________