[net.micro.cbm] Amiga - 68000 chip

michael3@garfield.UUCP (Mike Rendell) (08/15/85)

[]

  I am wondering why the Amiga uses the 68000 chip instead of the 68010?
The 68010 has been out for quiet a while (about a year?) so it was around
when the Amiga was being devoloped.  Also, would it be possible to upgrade
it to the 68010 (or maybe the 68020)?


					Mike Rendell
					michael3@garfield

csc@watmath.UUCP (Jan Gray) (08/26/85)

In article <3429@garfield.UUCP> michael3@garfield.UUCP (Mike Rendell) writes:
>[]
>
>  I am wondering why the Amiga uses the 68000 chip instead of the 68010?
>The 68010 has been out for quiet a while (about a year?) so it was around
>when the Amiga was being devoloped.  Also, would it be possible to upgrade
>it to the 68010 (or maybe the 68020)?
>
>
>					Mike Rendell
>					michael3@garfield

Unless you need the ability to complete a page-faulted instruction
you don't need a 68010.  The 68010 also gets you "loop mode" (although
I seem to remember unrolled loops are faster), a movable interrupt vector
base, and a few other things, but 68010s are probably a bit more expensive
than 68000s.

The 68010 is pin compatible with the 68000.

The 68020 on the other hand would be quite an improvement, but I doubt
it would sync well with the Amiga interleave-DMA-with-instruction scheme,
and it is of course not pin compatible.

Jan Gray

kurt@fluke.UUCP (Kurt Guntheroth) (08/28/85)

The amiga uses the 68000 chip exactly because it is less expensive and the
amiga does not require the 68010 extra capabilities of instruction restart.
The 68000 and 68010 are directly compatible and if you want to speed
everything up about 7-8%, you can just drop in a 68010 (assuming the 68000
is in a socket of course).
-- 
Kurt Guntheroth
John Fluke Mfg. Co., Inc.
{uw-beaver,decvax!microsof,ucbvax!lbl-csam,allegra,ssc-vax}!fluke!kurt

dal@tikal.UUCP (Don Ledford) (08/28/85)

------
In article <916@vax2.fluke.UUCP> kurt@fluke.UUCP (Kurt Guntheroth) writes:
>The amiga uses the 68000 chip exactly because it is less expensive and the
>amiga does not require the 68010 extra capabilities of instruction restart.
>The 68000 and 68010 are directly compatible and if you want to speed
>everything up about 7-8%, you can just drop in a 68010 (assuming the 68000
>is in a socket of course).
>-- 

I'm a software type and don't have access to the amiga schematics, but
I would caution against replacing the 68000 chip with a 68010 until
you know for sure it doesn't effect the shared access to the video RAM.
It may be that access is arbitrated by monitoring the instruction
fetch activity of the CPU (during fetch the DMA has a free shot at
the video RAM).  The 68010 doesn't need to perform fetches for certain
types of code loops (hence the speed improvement); this may cause
unacceptable delays for the video circuitry.

Speculation only. 

Don Ledford

granvold@tymix.UUCP (Tom Granvold) (08/29/85)

-
    Yes you can replace a 68000 with a 68010 in an Amiga, Atari ST, MAC or
any other machine that uses the 68000. The two chips are pin compatable.
There are two advanges that I know of for doing this. First, the 68010
can handle page faults where the 68000 cannot. Second, the 68010 can
internally hold short loops, 3 or 4 instructions, and therefore execute
them faster that the 68000 can.
    No, putting a 68010 in any of these machines will not probably work. The
reason is that the on some execptions, Motorola's name for interrupts, the
68010 saves more information on the stack than the 68000 does. This means 
that the OS will most likely need a couple of small changes. This is no
problem if one knows the OS and has the source. I would not count on
Commodore, Apple or Atari to do it for us.
    So to repleat, it will probably not work to replace the 68000 with a
68010 in an Amiga or other 68000 system. If someone in the S.F. bay area
would like to try an experiment, I have a 68010 chip that we can us. If
you have an Amiga, Atari ST or MAC and are willing to open it up to 
change the chip, I'd love to see if it works. Of course I can afford to
make this offer since it won't be my machine being messed with :-). I
don't have any of these machines yet. I am still debating over whether
to get an ST and save money or spend more and get the Amiga.

Tom Granvold
Tymnet

ucbvax!oliveb!tymix!granvold