🚀 go-pugleaf

In article <7160@sugar.hackercorp.com> peter@sugar.hackercorp.com (Peter da Silva) writes:
   In article <CEDMAN.90Nov28142350@lynx.ps.uci.edu> cedman@golem.ps.uci.edu (Carl Edman) writes:
   > A correct 68000 program runs unchanged on a 68030.

   Ah, then explain why Atari ST programs don't run on a 68020. There are lots of
   instructions that work differently between the 68000 and 68030, and any program
   that uses them will behave differently on different machines. Oh, you can say
   "but those aren't correct 68000 programs", which is all well and good but in
   the real world these instructions exist and are percieved as being useful to
   the sorts of folks who write manic games in assembler.

I haven't heard about the ST in a long time, but last time I checked,
the reason why current STs don't work with higher processors (in
contrast to the amiga, which has run higher processors almost
forever), is that the OS of the ST was written sloppily. OSes
sometimes have to use dirty programming, and as long as they do it
that is fine. Amiga OS has been written in a way which is compatible
with higher processors, ST OS hasn't. User programs for the ST should
run unmodified under higher processors.

   Basically, writing a portable program is harder the lower the level you write
   the program at. If you do everything through intuition in C, you're unlikely
   to cause headaches for Amiga 3000 users. If you do everything in assembly,
   it's a lot harder to keep all the differences between the different
   processors straight... because they become exposed to the programmer.

I really don't know about which "all the differences" you are talking
about. I've programmed both and there really aren't any
incompatibilities.  I'm all for using Intuition and not writing to the
screen memory directly. But you can do that just as well in assembler.
And intuition.library does not screen you from any processor
incompatibilities.

   I'm not saying "it's impossible to write a portable 68000 program in assembly",
   but rather "it's a whole lot harder to write one". Quit with the theoretical
   BS and look at the real world.

There are lots of 68030 instructions which don't run on a 68000.
Almost all 68000 instructions run on a 68030. The only minor
exceptions to this are quite obscure accesses which should only be
made in supervisor mode (in which no user programm should run) anyway.

If I may quote the "Processor book for the 680x0 family" with respect
to the 68020 (the translation is mine):

"The 68020 has been extended in many areas. Still it remains program
- compatible with the other CPUs in the family. Certain limitations
of compatibility affect routines which process exceptions. But on the
User-level the 68020 is capable to run all programs written for 680x0
family without changes."

Good enough ?


Theorectical Physicist,N.:A physicist whose  | Send mail
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