Screen truncated in Sega Master System?

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johannesbehr
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Screen truncated in Sega Master System?

Unread post by johannesbehr » Thu Jan 03, 2019 12:29 am

Hi everybody!

All games for Sega Master System I tried on my Odroid-Go have a truncated sceen :?:

I tried:
- Prince of Persia
- Castle of Illusion


What is the reason for this? Is this a known limitation?

Btw: The Odroid-Go is the cooles gadget I ever got :D !

crashoverride
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Re: Screen truncated in Sega Master System?

Unread post by crashoverride » Thu Jan 03, 2019 1:51 am

Can you provide a picture that shows the issue?

johannesbehr
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Re: Screen truncated in Sega Master System?

Unread post by johannesbehr » Thu Jan 03, 2019 3:41 pm

Thanks for your response!

Here come some Pictures, showing the games on the Odroid Go and on the Retro Pi... :)

Toggling screen scaling by the hotkeys also does not help.
Attachments
Odroid_Go-PrinceOfPersia.jpg
Odroid_Go-PrinceOfPersia.jpg (270.18 KiB) Viewed 361 times
Odroid_Go-CastleOfIllusion.jpg
Odroid_Go-CastleOfIllusion.jpg (248.21 KiB) Viewed 361 times
RetroPi-PrinceOfPersia.jpg
RetroPi-PrinceOfPersia.jpg (297.39 KiB) Viewed 361 times
RetroPi-CastleOfIllusion.jpg
RetroPi-CastleOfIllusion.jpg (94.91 KiB) Viewed 361 times

johannesbehr
Posts: 20
Joined: Thu Jan 03, 2019 12:21 am
languages_spoken: english
ODROIDs: Odroid-Go
Contact:

Re: Screen truncated in Sega Master System?

Unread post by johannesbehr » Thu Jan 03, 2019 4:50 pm

Hi Crashoverride,

I investigated a bit into the code and I guess the problem is the "console type detection" in loadrom.c
Maybe it is because if the rom has the string "TMR SEGA" at 0x7ff00 it always skips the detection.
I patched the PrinceOfPersia-Rom so that it has 0x55 instead 0x54 ("UMR SEGA" :-) ) and the game started with the correct resolution!

Probaly the console type detection needs to be fixed…

Greetings
Johannes

crashoverride
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Re: Screen truncated in Sega Master System?

Unread post by crashoverride » Thu Jan 03, 2019 4:51 pm

I tested both titles and they display correctly. The ROMs being used may be 'hacked' or otherwise modified. They appear to operate in GameGear mode rather than Master System.

johannesbehr
Posts: 20
Joined: Thu Jan 03, 2019 12:21 am
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Re: Screen truncated in Sega Master System?

Unread post by johannesbehr » Fri Jan 04, 2019 3:20 pm

Finally I found the solution:

Both games had a wrong region Information. So checking with a binary editor I saw that byte 0x7fff had the value 70 while the game was for Master System.
As explained here: http://www.smspower.org/Development/ROM ... fff05Bytes this would indicate a Game Gear-Game.

So by changing this byte to 40 both ROMs now run perfectly well!!

Thank you for your patience :-) !
Attachments
correkt_region.png
correkt_region.png (3.01 KiB) Viewed 303 times
wrong_region.png
wrong_region.png (3.1 KiB) Viewed 303 times

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