[HP41] mcode question polling point entries

[MeindertKuipers]

(03-22-2023 05:13 PM)Monte Dalrymple Wrote:  

(03-22-2023 04:09 PM)MeindertKuipers Wrote:  Hi mcode guru's,

I am struggling with some mcode using the HP41 polling entries, and I am probably messing up some registers. Is there any definition which CPU registers can be freely used and which must be restored during any of these polling entries?

From the comments in the HP-41 OS listing: Plug-in ROMs must preserve C[10:3] and return to RMCK10 with hex mode, P selected, Status Set 0 up, and chip 0 selected.

So, everything else is fair game, including subroutine levels. But if you're using the I/O service entry (FF8) in some case no subroutine levels are available. That's the only restriction that I sometimes forget about.

Monte

I do not think the subroutine levels are an issue. I am patching the PRINTER ROM, and that uses at least 2 levels in the xFF8 entry. And for my application it is not an issue at all, no additional subroutines planned