How to disassemlbe/edit PSX BIOS ?

[a4451137]

Hello
What tool use for disassemlbe PSX BIOS ?
How this BIOS is secured/packed ?

example.
How to change playstation logo boot ?


In bios is checksum ?

Can I use IDA to disassemble BIOS ?

[Administrator]

Search for specific data type headers such as TIM, TMD and HMD using IDA. It wont be easy so good luck to you

[a4451137]

Search for specific data type headers such as TIM, TMD and HMD using IDA. It wont be easy so good luck to you

So many years and no one hack it
It is possibly to create my own menu ?

my point is: you can make your own menu (psx-exe like) with the same pics (ripped) of background or even better!, then compile it from 80030000 start addres, and put it to 18000 to the new bios (without header 0x800).
bios shell is justa code - nothing special)))

How someone created modchip without sourcecode bios ?

[Orion_]

I don't think this logo is as image data in the bios.
from what you can see in the vram during bios boot, you have a font loaded for the SONY text, and the middle logo might be a simple gradient polygon. (as it is animated remember)

[a4451137]

But How modchip was created without bios source code ?

[Administrator]

The BIOS has got nothing to do with how modchips work (not including stealth). Modchips were made by hackers reverse engineering the system to know exactly what they had to do in order to get the PSX to boot copies.

[Tommy]

The BIOS has got nothing to do with how modchips work (not including stealth). Modchips were made by hackers reverse engineering the system to know exactly what they had to do in order to get the PSX to boot copies.

They spoof a signal between the CD drive and the outer hardware to make it look like an appropriate signal is on disc at an appropriate place, right? So the BIOS executes normally, believing the CD drive to have told it that a valid disc is inserted.

... and the middle logo might be a simple gradient polygon. (as it is animated remember)

It definitely is: one of the emulators includes a note in either its manual or its graphics setup menu that you can enable rendering of quads as quads rather than as pairs of triangles to get slightly less subjective distortion but at the cost of the gradient on the startup logo not rendering correctly.

So many years and no one hack it
It is possibly to create my own menu ?

Probably you'd get good mileage out of a standard R3000a disassembly and then differencing between the SCPH-1001 and SCPH-1002 BIOSes. The no-disc-inserted menu is entirely different in Europe from what it is in the US but obviously anything that game code may call is intentionally the same.

[AmiDog]

So many years and no one hack it

Well, nocash (martin korth) has written a complete BIOS clone for his emulator, so he has probably spent some time hacking the original BIOS.

[a4451137]

IDA PRO support PSX BIOS image:

[org]

SCPH-1001 reversing:

https://github.com/ogamespec/psxdev/tree/master/reverse

IDA 6.5 project in SCPH1001.zip

[Administrator]

SCPH-1001 reversing:

https://github.com/ogamespec/psxdev/tree/master/reverse

IDA 6.5 project in SCPH1001.zip

Very cool. Would be nice to get the complete source from Sony though

[locarno]

SCPH-1001 reversing:

https://github.com/ogamespec/psxdev/tree/master/reverse

IDA 6.5 project in SCPH1001.zip

Very cool. Would be nice to get the complete source from Sony though

Any update on this ? Sony released complete source or it leaked from somewhere ?

[CodeAsm]

SCPH-1001 reversing:

https://github.com/ogamespec/psxdev/tree/master/reverse

IDA 6.5 project in SCPH1001.zip

Very cool. Would be nice to get the complete source from Sony though

Any update on this ? Sony released complete source or it leaked from somewhere ?

Last change on their wiki was in december I think, git was 2 months ago.

Sony released complete source or it leaked from somewhere ?

I hope you reread what that project is about, the meaning of the word "reverseing" is important here. ( https://en.wikipedia.org/wiki/Reverse_engineering )
Very intresting still tho, amazing what some people can figure out with IDA and programming knowledge. Hope more discoveries will be made.