Game ROMs that runs at 0000h

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By gdx

Enlighted (4197)

gdx's picture

05-03-2021, 13:00

Sometimes we are so sure but yet we have wrong. It also happens to everyone.
You can easily check it yourself with the BlueMSX debugger by using a point break. You just need a 48kB Rom with the address modified. In addition, Colecovision Roms converted of 48/64kB for MMM use this method. Some games from Sony and few others use also this method using mirrors. (Crazy train, Decathlon, Sparkie, etc)

By lintweaker

Champion (365)

lintweaker's picture

05-03-2021, 13:01

gdx wrote:

Sometimes we are so sure but yet we have wrong. It also happens to everyone.
You can easily check it yourself with the BlueMSX debugger by using a point break. You just need a 48kB Rom with the address modified. In addition, Colecovision Roms converted of 48/64kB for MMM use this method. Some games from Activision and Sony use also this method using mirrors. (Crazy train, Sparkie, etc)

Never too late to learn something new. The BIOS must be doing this via some code page 3 (i.e. enable ROM in page 0 and then jumping to it)?

By gdx

Enlighted (4197)

gdx's picture

05-03-2021, 13:29

The most signifiant 2 bits of the INIT address corresponding to the page to be selected to run the Rom.

By Grauw

Ascended (9690)

Grauw's picture

05-03-2021, 13:53

lintweaker wrote:

Never too late to learn something new. The BIOS must be doing this via some code page 3 (i.e. enable ROM in page 0 and then jumping to it)?

Yep, interslot calls work like that.

By gdx

Enlighted (4197)

gdx's picture

05-03-2021, 16:05

gdx wrote:

So we can display our own logo or do something else before the MSX logo but it will not work on Turbo R (nor on MSX1 of course).

In fact it depends on the Sub-Rom location. Korean MSX2s and few others do not have the Sub-ROM in slot 3-x.

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