mega65 target doesn't need soft stack about llvm-mos

[ki-bo]

This is a very good point. Calling KERNAL routines may either need switching to a temporary 8 bit stack on a separate page, or one could make the use of the soft stack configurable when building the application.

I see uses of the compiler where the ROMs are banked out completely and all I/O routines are written with no dependencies to ROM routines. This will allow to use more RAM, and games will probably make use of that. Having a cpu stack instead of a soft stack should provide some performance gain still.

[lgblgblgb]

@ki-bo This is true, for sure, just I would like to add, that then any KERNAL routine call needs more care since those routines are probably not so much aware of 16 bit stack pointer usage, and there can be cases when this matters.

[lgblgblgb]

Also IRQ handler must aware of this, which is used by the ROM for eg. kbd scanning/etc. But indeed, I think so too, using the CPU capabilities of MEGA65 (or C65) the fact they have 16 bit stack pointer mode and stack relative addressing mode would be a huge gain, not only because of speed/performance, but maybe the code can be smaller as well?

[ki-bo]

I just checked with a current Mega65 ROM. The IRQ itself seems to be unaffected, as it just doesn't care where the stack actually lives. But I agree that certain ROM routines (eg. ones banking in ROM) will have issues if your stack is actually moved somewhere else. I think, switching to the original stack page at $100 right before the jsr into ROM and then switching it back to the original 16 bit location afterwards might still work, though.