[HP41] mcode question polling point entries

[Ángel Martin]

(03-23-2023 04:07 PM)MeindertKuipers Wrote:  Getting a bit closer now.
According to the VASM listings:

Quote:** all subroutine levels are available except in I/O service entry.
** if PKSEQ is set then I/O service routines must either preserve three subroutine
** returns on the subroutine stack or else terminate the partial key sequence.

And with the quoted CAT from OS/X I guess we are in PKSEQ. But my code does not use any extra subroutines, and without using N my code works with OS/X. The moment I change N the PSEQ is disrupted, but I still have to find out how N is used and what to do about it.
Use of any other register is out of the question, these are all in use unfortunately ...

Hmmm... I'm not aware of any register restriction in the I/O polling point - at least not in general. However there may be something else at play here if the routines use registers with system data information. If the previous module alters the system data (in its I/O polling chance) then the following module will not have the expected contents.

I suspect that in the OS/X case there is some of that going on but I should review the code again. BTW you can try with the original CCD Module and see if it shows the same issue (I bet it does, since the OS/X uses the same code for this).

I'll report what I find out, it's not the easiest piece of code (very complex indeed) and I never got the source code so will take a little effort.

PS. As far as the YFNX case plugged in a lower page than the OS/X - I believe Monte figured out the reason why that happens. I don't remember the details but I don't recall that registers were involved...