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Some games use the information left by the bios on C000 to know where they're being booted from.
If I am not wrong, some games rely on the bios to set the stack pointer.
Is there any other bios leftover that makes game run(possibly even because of bugs in the game)?

I noticed two things:
bios v. 1.3 initializes the whole ram to 0. Is there any game that does not work properly without this initialization?
alex kidd bios does not initialize to 0 (is there thus any game that glitches because of this)?
why does alex kidd bios write to C004?

p.s. I also found this thread
http://www.smspower.org/forums/1567-SMSZ80StackPointer
was something new found since then?

Not sure if this is of use. Its about the official power base converter for the mega drive/genesis and how it set the stack pointer. There were a few games mentioned that relied on the stack pointer being set to work.

http://www.smspower.org/forums/14084-PowerBaseConverterInfo

Thank you, indeed I think the SP is one of the things that need to be set for some games.
My wonder was if there are other games that have bugs (e.g. code that uses memory/registers/vdp memory not initialized by the game itself) that went undetected during testing because the machine always started in the state left by the bios.

Yes, Codemasters even managed to release some games unaware that they don't work on original model systems.

do you mean because of the vdp differences or because of something in RAM?

It's VDP compatibility. I think there's also some games which fail due to mapper compatibility, as the earlier BIOSes don't set the paging registers for slots 0 and 1, and the game doesn't default them.

you mean the 'SMS2' games? Do you think they didn't know the 'extra high' video mode wasn't available on the first model?

sverx wrote

you mean the 'SMS2' games? Do you think they didn't know the 'extra high' video mode wasn't available on the first model?

Or maybe they didn't care at all....

More likely they didn't test it.

Author	Message
kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	Games dependence on bios Posted: Fri Feb 23, 2018 1:59 am
	Some games use the information left by the bios on C000 to know where they're being booted from. If I am not wrong, some games rely on the bios to set the stack pointer. Is there any other bios leftover that makes game run(possibly even because of bugs in the game)? I noticed two things: bios v. 1.3 initializes the whole ram to 0. Is there any game that does not work properly without this initialization? alex kidd bios does not initialize to 0 (is there thus any game that glitches because of this)? why does alex kidd bios write to C004? p.s. I also found this thread http://www.smspower.org/forums/1567-SMSZ80StackPointer was something new found since then?

wasup Joined: 05 Nov 2014 Posts: 435 Location: Auckland - NZ	Posted: Sun Feb 25, 2018 8:02 am
	Not sure if this is of use. Its about the official power base converter for the mega drive/genesis and how it set the stack pointer. There were a few games mentioned that relied on the stack pointer being set to work. http://www.smspower.org/forums/14084-PowerBaseConverterInfo

kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	Posted: Sun Feb 25, 2018 11:50 pm
	Thank you, indeed I think the SP is one of the things that need to be set for some games. My wonder was if there are other games that have bugs (e.g. code that uses memory/registers/vdp memory not initialized by the game itself) that went undetected during testing because the machine always started in the state left by the bios.

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14744 Location: London	Posted: Mon Feb 26, 2018 12:08 am
	Yes, Codemasters even managed to release some games unaware that they don't work on original model systems.

kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	Posted: Fri Mar 02, 2018 6:02 am
	do you mean because of the vdp differences or because of something in RAM?

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14744 Location: London	Posted: Fri Mar 02, 2018 6:58 am
	It's VDP compatibility. I think there's also some games which fail due to mapper compatibility, as the earlier BIOSes don't set the paging registers for slots 0 and 1, and the game doesn't default them.

sverx Joined: 05 Sep 2013 Posts: 3827 Location: Stockholm, Sweden	Posted: Fri Mar 02, 2018 12:38 pm
	you mean the 'SMS2' games? Do you think they didn't know the 'extra high' video mode wasn't available on the first model?

kusfo Joined: 29 Mar 2012 Posts: 886 Location: Spain	Posted: Fri Mar 02, 2018 12:55 pm
kusfo Joined: 29 Mar 2012 Posts: 886 Location: Spain	sverx wrote you mean the 'SMS2' games? Do you think they didn't know the 'extra high' video mode wasn't available on the first model? Or maybe they didn't care at all....

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14744 Location: London	Posted: Fri Mar 02, 2018 1:58 pm
	More likely they didn't test it.

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