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From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: TT RAM
Message-ID: <2310@atari.UUCP>
Date: 20 Sep 90 19:00:03 GMT
References: <3107@medusa.informatik.uni-erlangen.de> <2304@atari.UUCP> <3118@medusa.informatik.uni-erlangen.de>
Organization: Atari Corp., Sunnyvale CA
Lines: 25

csbrod@medusa.informatik.uni-erlangen.de (Claus Brod ) writes:
>apratt@atari.UUCP (Allan Pratt) writes:
>>VME memory is not accessible to SCSI, and you should use the buffer
>>pointed to by the _FRB cookie.

>Hum, hum, and how do we detect that some RAM is a) VME RAM and b) 16
>bits wide? Did I miss something here?

My comment about VME RAM was not clear.  In the TT030, which is the
full name of the machine that's now available, there are two kinds of
VME address space: A24/D16 and A16/D8.  These are not 32 bits wide, so
the SCSI chip can't access them.  The memory map, telling where in
memory those segments appear, should be part of the TT documentation:
if it's not, it will be.

The VME expansion isn't really for RAM anyway: VME RAM for a TT is
expensive and slow -- slow because it's only 16 bits wide, because it
goes through the VME bus, and because it's not cacheable by the 68030.
You're far more likely to want to put a video display card there, or
extra serial ports or something.  For those, the fact that the
processor can't get at the memory at full speed won't hurt too much.

============================================
Opinions expressed above do not necessarily	-- Allan Pratt, Atari Corp.
reflect those of Atari Corp. or anyone else.	  ...ames!atari!apratt