Re: Do ROM 03 IIgs's have some problems?

[dempson@actrix.gen.nz (David Empson)]

Mitchell Spector <mitch2gs@hotmail.com> wrote:

> dempson@actrix.gen.nz (David Empson) wrote:
> 
> >skylarking <petsoundsnz@gmail.com> wrote:
> >
> >> I have one and sometimes I can't get into the control panel with
> >> control-apple-esc
> >
> >Ctrl-Apple-Esc generates an interrupt, so if the program you are
> >currently running (typically a game or similar) has locked out
> >interrupts, then nothing will happen when you push this key sequence.
> >
> >This isn't specific to a ROM 3.
> 
>     Although there was a key press that seemingly allowed you to bypass
> the lock out specifically on the ROM 3 (not all programs, only a handful).
> That sequence was: Apple-Shift-Control-Esc
> 
>     I discovered it by accident years ago. Can't remember off hand if it's
> firmware or hardware related, or even if it's a documented feature. 

First I've heard of it. My ROM 3 IIgs is at work so I can't verify this.

The only way it could actually bypass an interrupt lockout would be if
it generated an NMI or hardware reset instead of IRQ.

There is already the Ctrl-Option-Reset sequence which lets you go to the
control panel in the process of resetting the computer (can't resume
execution - only way out is to continue restarting).

NMI has the potential to destroy floppy disks (if you do an NMI during a
write operation) so it isn't used for anything under normal
circumstances.  Resuming after an NMI is also difficult, so it is best
handled as a precursor to resetting.  This wouldn't make it any better
than Ctrl-Option-Reset, so not much point.

The only other option which occurs to me would be that some firmware
routines or OS calls could check if Ctrl-Shift-Apple-Esc had been
pressed at some point recently, and if so, go to the Desk Accessory menu
before returning from the call.  This would allow the control panel to
be accessed even if interrupts were locked out over an extended period,
as long as the application called a firmware or OS function which did
this check.

If this feature is only present on a ROM 3 IIgs, it would be more likely
to be a firmware routine doing the check.
-- 
David Empson
dempson@actrix.gen.nz