680x0->PPC (or Coldfire)??

Aaron J. Grier aaron at frye.com
Fri Jun 14 23:52:10 UTC 2002

On Fri, Jun 14, 2002 at 12:00:45PM -0400, Smith, Gene wrote:
> Does anybody out there have any feel for how hard it is to convert
> from 68k to Power PC or Coldfire? Have a 68020 board that is 98%
> assemby and might want to upgrade the processor to something
> newer/faster/lower-power with minimal code rewrite.

depending on what addressing modes your 020 code uses, coldfire could be
as simple as a recompile.

a project of ours considered moving from 68331 to coldfire, but the
existing assembly code liberally sprinkled with address register
indirect with base displacement:

move.l  (_pit_counter,a5),d1

which would work on the coldfire if the base displacement fits into 8 or
16 bits, but that's wasn't typical for the code we were planning on

the 683xx might fill the bill if you're just looking to cut costs...
but be aware there are a couple 020 addressing modes (PC and memory pre-
and postindexed indirect) that aren't supported on the cpu32.

of course a better solution might be to start migrating parts of your
assembly application to C running with RTEMS!  :)

  Aaron J. Grier  |   Frye Electronics, Tigard, OR   |  aaron at frye.com

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