Custom BIOS from cart
Posted: Tue Nov 18, 2014 12:02 pm
Hi there,
For debug/dev purpose, I'd like to make a custom bios.
This bios could be used on emulator (standard bios), on hardware (standard bios to burn), on cart (to avoid hardware update)
I read some posts like
viewtopic.php?p=14320#14320
viewtopic.php?p=21772#21772
viewtopic.php?t=1746
, some points should be taken in account to handle the 2 ways
- standard bios is loaded form 0x0 while cart bios is loaded from 0x400000 (base adress)
- header is different (not sure exactly how...)
- info of sub cpu must be defined at 0x1A8+
- region security code must be added at 0x200 and should be the same that the one on standard bios of the MCD used
- custom main bios should be added afer region security code
- subbios is zipped using Kosinski
So basically, I can't take any bios I want and burnt it on a cart
but i could take the subcpu, pcm driver and security code from a bios, and add them on a custom bios
So
- what the bios did before giving the hand to the cart bios ? nothing , only looking for cart bios first ?
- is there a way to bypass this tmss pair which ask for a custon bios for each bios existing ?
- what is the "best" bios available to start with ?
- is there some bios which doesn't work with some MCD model ?for ex if I take a region free Jap MCD1 Bios, will it work on a European MCD2 ? I assume XEyes, JVC, CDX are not valid ...?
- is there some bios which doesn't handle cart bios ? (first jap model?)
- a cart bios is only a standard card with /CART not grounded (VCC or NC ?), nothing more like address mapping , right ?
anything more to know ?
For debug/dev purpose, I'd like to make a custom bios.
This bios could be used on emulator (standard bios), on hardware (standard bios to burn), on cart (to avoid hardware update)
I read some posts like
viewtopic.php?p=14320#14320
viewtopic.php?p=21772#21772
viewtopic.php?t=1746
, some points should be taken in account to handle the 2 ways
- standard bios is loaded form 0x0 while cart bios is loaded from 0x400000 (base adress)
- header is different (not sure exactly how...)
- info of sub cpu must be defined at 0x1A8+
- region security code must be added at 0x200 and should be the same that the one on standard bios of the MCD used
- custom main bios should be added afer region security code
- subbios is zipped using Kosinski
So basically, I can't take any bios I want and burnt it on a cart
but i could take the subcpu, pcm driver and security code from a bios, and add them on a custom bios
So
- what the bios did before giving the hand to the cart bios ? nothing , only looking for cart bios first ?
- is there a way to bypass this tmss pair which ask for a custon bios for each bios existing ?
- what is the "best" bios available to start with ?
- is there some bios which doesn't work with some MCD model ?for ex if I take a region free Jap MCD1 Bios, will it work on a European MCD2 ? I assume XEyes, JVC, CDX are not valid ...?
- is there some bios which doesn't handle cart bios ? (first jap model?)
- a cart bios is only a standard card with /CART not grounded (VCC or NC ?), nothing more like address mapping , right ?
anything more to know ?