System variables (again!)

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Por Bengalack

Hero (580)

Imagen del Bengalack

14-05-2022, 07:57

Great insight here! Thanks. But... if you are not using BIOS, and use your own ISR, and you never return from your program until there is a reset(as is it a rom/cartridge), I can't see how the ram "hi-jacking" affects anything. If there is a problem with this approach, it is the choice of not using BIOS-calls. This may cause future incompatibility... which is a fun thing to discuss regarding a retro-machine Smile Yes, I know about Nishi's latest works... 30 years later Smile

Por Micha

Resident (50)

Imagen del Micha

14-05-2022, 11:11

Bengalack wrote:

If there is a problem with this approach, it is the choice of not using BIOS-calls.

Are there actually any machines that don't use the "standard" ports for the VDP, PSG, keyboard and joysticks? Is there an overview or a list on this?

And the other way around: how much software/games are out there that handle hardware directly without using BIOS calls ?

Por Bengalack

Hero (580)

Imagen del Bengalack

14-05-2022, 17:22

Micha wrote:
Bengalack wrote:

If there is a problem with this approach, it is the choice of not using BIOS-calls.

Are there actually any machines that don't use the "standard" ports for the VDP, PSG, keyboard and joysticks? Is there an overview or a list on this?

Other people here know this area better, but AFAIK there is this, and the like: https://www.msx.org/wiki/Neos_MA-20

Por Bengalack

Hero (580)

Imagen del Bengalack

03-07-2022, 10:31

Micha wrote:

If you do have your own ISR and you don't use BIOS calls and you have all other interrupts disabled then it should be safe to use F380-FFFE...

What "all other interrupts"? I'm on IM1, and purely running my own code on 0038h.

Por aoineko

Champion (446)

Imagen del aoineko

03-07-2022, 14:16

If you use you own ISR and don't use BIOS routines you can use all the RAM freely (except FFFFh).
In your boot code, you can backup the usefull BIOS information in your own RAM area.
For exemple, in the game Final Smash I backup: Version config (002B, 002C and 002D), EXPTBL (FCC1) and SLTTBL (FCC5).

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