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From: scotty@l5comp.UUCP (Scott Turner)
Newsgroups: comp.sys.m68k,comp.sys.atari.st,comp.sys.amiga
Subject: Re: the 68070 - has it left hyperspace yet?
Message-ID: <110@l5comp.UUCP>
Date: Sat, 9-May-87 19:39:21 EDT
Article-I.D.: l5comp.110
Posted: Sat May  9 19:39:21 1987
Date-Received: Sun, 10-May-87 11:42:37 EDT
References: <280@spectrix.UUCP>
Reply-To: scotty@l5comp.UUCP (Scott Turner)
Organization: L5 Computing, Edmonds, WA
Lines: 34
Keywords: 68070, signetics, Philips, mac/st/amiga UN*X
Summary: Info on 68070 and Amiga's vs MMU's
Xref: mnetor comp.sys.m68k:469 comp.sys.atari.st:3360 comp.sys.amiga:4693

I have no knowledge of pricing or availablity but Signetics did break down and
send me a large information package about this device.

1. The chip is NOT pin compatible with anything except itself (grin).
2. The MMU is a warped 68451.
3. The chip uses 68010 style exception frames so it can use the MMU properly,
but that's ALL it takes from the 68010. No virtual CPU support ie move sr,ea
isn't priv'd.
4. The opcodes execute faster than their 68000 counterparts. Signetics has used
a wild 2X clock scheme. Where a 68000 counts T states off a 8MHz clock the 68070
counts it's states off a 16MHz clock BUT uses an 8MHz buss clock! This method
allows them finer granularity in the timing of the execution unit.
5. It's a cute chip but I doubt we'll see too many retrofits, as for the expected
design-ins... Wouldn't you rather have a MC68020?? (grin)

Trying to put this chip into the Amiga would raise all sorts of issues so I
don't blame C-A for not doing it. (I do think it was silly to not use the 68010
though) The MMU for example would kill most message ports. If C-A had been
thinking ahead they would have included an MEMF type for a true "public"
memory type. If this had been done then message ports could have been allocated
using this memory type and on MMU systems this would return a pointer into a
shared memory page. Alas it is too late now and we have RJ running around saying
how "lucky" we are to not have an MMU because of all the overhead in passing
messages back and forth in such systems. Some people should stick to designing
game machines, grin. It's surprising that this concept of shared memory pages
was missed since they picked up on the UN*X concept of having a slow file
system to cut the legs from under the machine.

Scott Turner

L5 Computing, the home of Merlin, Arthur, Excalibur and the CRAM.
GEnie: JST | UUCP: stride!l5comp!scotty | 12311 Maplewood Ave; Edmonds WA 98020
If Motorola had wanted us to use BPTR's they'd have built in shifts on A regs
[ BCPL? Just say *NO*! ] (I don't smoke, send flames to /dev/null)