Re: 6502 illegal opcodes questions

["Michael" <michael.pohoreski@gmail.com>]

Michael J. Mahon wrote:
> The Apple ROM was not significantly changed until the //e, where much
> of the actual code was placed in a bank-switched area.  Much of the F8
> region became stubs at documented entry points vectoring to the actual
> routines.  Updating the F8 region of the ROM was known to be a minefield
> of compatibility issues.
>
> The notion of defining the ROM entry points more architecturally was
> not widespread at the time the Apple II was designed, and the impact
> of the subsequent loss of control over ROM code became a problem.

This is related to another hobby of mine -- the HP48 calculator (which
in a lot of ways, has the same "Apple" feel.)  It had the same problem,
all though it wasn't as bad, since there became known 'entry points' of
the system ROM; i.e. SYSEVAL on the HP28 which exposed the problem to
the general public.  (You know how curious engineers/geeks are when
something has "undocumented" written all over it.  ;-)

I'll agree that it was not widespread, but it was known. The question
is when?
Woz did work at HP -- when did the calculator people come up with a
solution?  And did Woz know about it?



> (I've always wondered how much "compatibility issues" and how much
> "renegotiation issues" factored into the decision to never update
> the Applesoft ROMs to fix bugs...)
>
> Later systems used a combination of less documentation and more
> complexity to make calls into the middle of ROM less likely.  Still
> not an ideal solution, but one well adapted to the Apple II.  ;-)

It certainly looks like everyone was too busy writing their own code,
since the ROM code wasn't all that usefull.

Cheers