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My first post in here, 'cos it's a bit technical.

I have several roms which differ from the Meka-recognised rom by one byte; this byte is in different places but it's always FE in the recognised rom and FF in the unrecognised one. Some examples (fc output):

Captain Silver
0003164B: FF FE

Desert Strike
00063111: FF FE

Gauntlet
000072F5: FF FE

Sagaia
0003AD51: FF FE

Sonic Chaos
00027EE9: FF FE

Tom and Jerry - The Movie [A]
0003C0EB: FF FE
0003CEAB: FF FE

(two bytes but the same difference)

I have three roms Meka flags as having one byte wrong - for all three, the wrong byte is FF instead of FE.

Is there a reason why these bad bytes are always FF? Or are they not code at all, but a flag of some sort (eg. country code), which would explain the peculiarities of it?

Maxim

It's for SMS Checker...

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> My first post in here, 'cos it's a bit technical.

You're welcome! :)

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> I have several roms which differ from the Meka-recognised rom by one byte; this byte is in different places but it's always FE in the recognised rom and FF in the unrecognised one. Some examples (fc output):

[...]

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> I have three roms Meka flags as having one byte wrong - for all three, the wrong byte is FF instead of FE.
> Is there a reason why these bad bytes are always FF? Or are they not code at all, but a flag of some sort (eg. country code), which would explain the peculiarities of it?

No reasons.
I guess it is just a coincidence that the error is the same, or maybe some lame ROM distribution site found amusing to modify roms this way to recognize roms downloaded from his site -sic-

In your examples, except Desert Strike, you are able to check out which is the right ROM with the checksum.
However the location of the bad byte in Desert Strike is beyond the 256 kb so it is not included in the checksum.

The one listed in MEKA *should* be ok, but I'll redump Desert Strike to verify.

I just redumped it and the one recognized by MEKA is the good one.

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> > My first post in here, 'cos it's a bit technical.

> You're welcome! :)

Thanks :o)

(... bad byte always FE -> FF)

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> No reasons.
> I guess it is just a coincidence that the error is the same, or maybe some lame ROM distribution site found amusing to modify roms this way to recognize roms downloaded from his site -sic-

Very odd coincidence, very odd thing to do to mark the roms (you could add a footer or stick something in a header). I didn't mention that GoodSMS thinks they're all bad dumps.

I think I'll flag them up as one byte wrong. I'm thinking of making a program to fix up the slightly-bad dumps, BTW (or maybe I could meka.pat them - if I knew the Meka CRCs).

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> In your examples, except Desert Strike, you are able to check out which is the right ROM with the checksum.

Er... how? I searched most of the tech docs for "check" and drew a blank. Anyone made a checksummer (or sumchecker)? Anyone want one?

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> However the location of the bad byte in Desert Strike is beyond the 256 kb so it is not included in the checksum.

> The one listed in MEKA *should* be ok, but I'll redump Desert Strike to verify.

(later verified)

So it's definitely a bad byte, not an actual difference? Righty-ho.

Oh, you might want to use the info I gave to construct these roms and add them to meka.nam - none of them are recognised.

Maxim

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> > In your examples, except Desert Strike, you are able to check out which is the right ROM with the checksum.

> Er... how? I searched most of the tech docs for "check" and drew a blank. Anyone made a checksummer (or sumchecker)? Anyone want one?

Thanks to Mike G, I now have two... didn't they ought to be in Software Tools, though?

Maxim

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> Thanks to Mike G, I now have two... didn't they ought to be in Software Tools, though?

Probably :)
Anyway, they are both buggy in certain cases. I have now figured out some missing parts of the header so I will write a tool for it as soon as possible, and which should be included in the next version of MEKA.

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> Anyway, they are both buggy in certain cases.

But if one version of a game passes as OK and the rest don't, it's fair to say that the passed one is a good dump?

Reason being, I have an Meka-unrecognised Street Fighter 2 here which passes the CRC test, but the [A] and [B] versions Meka knows don't.

Maxim

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> Reason being, I have an Meka-unrecognised Street Fighter 2 here which passes the CRC test, but the [A] and [B] versions Meka knows don't.

Where did you got it from ?
I wonder if it is a hack or what. Anyway. SF2 is not perfectly dumped as far as I know (the guy who dumped it left a few bad bytes in it). This is one thing i have to do since a year, and I always forget :) hmm.. I'll do it tonight!

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> > Reason being, I have an Meka-unrecognised Street Fighter 2 here which passes the CRC test, but the [A] and [B] versions Meka knows don't.

> Where did you got it from ?

Via SMS Checker - someone mailed it to me.

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> I wonder if it is a hack or what. Anyway. SF2 is not perfectly dumped as far as I know (the guy who dumped it left a few bad bytes in it). This is one thing i have to do since a year, and I always forget :) hmm.. I'll do it tonight!

Well, the actual chacksum is the same, so either someone was clever enough to hack it so the checksum matched (unlikely if it's a CRC) or it's a third, perfect (for the first 256K at least) dump.

Maxim

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> Well, the actual chacksum is the same, so either someone was clever enough to hack it so the checksum matched (unlikely if it's a CRC)

It is not really a CRC and it's not possible to find out which data has to be modifed to get it to a "good dump", unless of course there is noticable pattern which is broken somewhere..

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>or it's a third, perfect (for the first 256K at least) dump.

I'll redump mine ASAP and see.

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> I'll redump mine ASAP and see.

And...? (just wondering...)

Maxim

Author	Message
Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Rom differences Posted: Sun Sep 17, 2000 12:32 pm
	My first post in here, 'cos it's a bit technical. I have several roms which differ from the Meka-recognised rom by one byte; this byte is in different places but it's always FE in the recognised rom and FF in the unrecognised one. Some examples (fc output): Captain Silver 0003164B: FF FE Desert Strike 00063111: FF FE Gauntlet 000072F5: FF FE Sagaia 0003AD51: FF FE Sonic Chaos 00027EE9: FF FE Tom and Jerry - The Movie [A] 0003C0EB: FF FE 0003CEAB: FF FE (two bytes but the same difference) I have three roms Meka flags as having one byte wrong - for all three, the wrong byte is FF instead of FE. Is there a reason why these bad bytes are always FF? Or are they not code at all, but a flag of some sort (eg. country code), which would explain the peculiarities of it? Maxim It's for SMS Checker...

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Posted: Sun Sep 17, 2000 5:18 pm
	Quote > My first post in here, 'cos it's a bit technical. You're welcome! :) Quote > I have several roms which differ from the Meka-recognised rom by one byte; this byte is in different places but it's always FE in the recognised rom and FF in the unrecognised one. Some examples (fc output): [...] Quote > I have three roms Meka flags as having one byte wrong - for all three, the wrong byte is FF instead of FE. > Is there a reason why these bad bytes are always FF? Or are they not code at all, but a flag of some sort (eg. country code), which would explain the peculiarities of it? No reasons. I guess it is just a coincidence that the error is the same, or maybe some lame ROM distribution site found amusing to modify roms this way to recognize roms downloaded from his site -sic- In your examples, except Desert Strike, you are able to check out which is the right ROM with the checksum. However the location of the bad byte in Desert Strike is beyond the 256 kb so it is not included in the checksum. The one listed in MEKA should be ok, but I'll redump Desert Strike to verify.

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Desert Strike.. Posted: Sun Sep 17, 2000 5:21 pm
	I just redumped it and the one recognized by MEKA is the good one.

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Mon Sep 18, 2000 11:33 pm
	Quote > > My first post in here, 'cos it's a bit technical. > You're welcome! :) Thanks :o) (... bad byte always FE -> FF) Quote > No reasons. > I guess it is just a coincidence that the error is the same, or maybe some lame ROM distribution site found amusing to modify roms this way to recognize roms downloaded from his site -sic- Very odd coincidence, very odd thing to do to mark the roms (you could add a footer or stick something in a header). I didn't mention that GoodSMS thinks they're all bad dumps. I think I'll flag them up as one byte wrong. I'm thinking of making a program to fix up the slightly-bad dumps, BTW (or maybe I could meka.pat them - if I knew the Meka CRCs). Quote > In your examples, except Desert Strike, you are able to check out which is the right ROM with the checksum. Er... how? I searched most of the tech docs for "check" and drew a blank. Anyone made a checksummer (or sumchecker)? Anyone want one? Quote > However the location of the bad byte in Desert Strike is beyond the 256 kb so it is not included in the checksum. > The one listed in MEKA should be ok, but I'll redump Desert Strike to verify. (later verified) So it's definitely a bad byte, not an actual difference? Righty-ho. Oh, you might want to use the info I gave to construct these roms and add them to meka.nam - none of them are recognised. Maxim

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Checksums Posted: Tue Sep 19, 2000 7:57 pm
	Quote > > In your examples, except Desert Strike, you are able to check out which is the right ROM with the checksum. > Er... how? I searched most of the tech docs for "check" and drew a blank. Anyone made a checksummer (or sumchecker)? Anyone want one? Thanks to Mike G, I now have two... didn't they ought to be in Software Tools, though? Maxim

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Re: Checksums Posted: Tue Sep 19, 2000 8:55 pm
	Quote > Thanks to Mike G, I now have two... didn't they ought to be in Software Tools, though? Probably :) Anyway, they are both buggy in certain cases. I have now figured out some missing parts of the header so I will write a tool for it as soon as possible, and which should be included in the next version of MEKA.

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Re: Checksums Posted: Wed Sep 20, 2000 7:47 pm
	Quote > Anyway, they are both buggy in certain cases. But if one version of a game passes as OK and the rest don't, it's fair to say that the passed one is a good dump? Reason being, I have an Meka-unrecognised Street Fighter 2 here which passes the CRC test, but the [A] and [B] versions Meka knows don't. Maxim

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Re: Checksums Posted: Thu Sep 21, 2000 6:29 am
	Quote > Reason being, I have an Meka-unrecognised Street Fighter 2 here which passes the CRC test, but the [A] and [B] versions Meka knows don't. Where did you got it from ? I wonder if it is a hack or what. Anyway. SF2 is not perfectly dumped as far as I know (the guy who dumped it left a few bad bytes in it). This is one thing i have to do since a year, and I always forget :) hmm.. I'll do it tonight!

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	SF2 Posted: Thu Sep 21, 2000 7:08 pm
	Quote > > Reason being, I have an Meka-unrecognised Street Fighter 2 here which passes the CRC test, but the [A] and [B] versions Meka knows don't. > Where did you got it from ? Via SMS Checker - someone mailed it to me. Quote > I wonder if it is a hack or what. Anyway. SF2 is not perfectly dumped as far as I know (the guy who dumped it left a few bad bytes in it). This is one thing i have to do since a year, and I always forget :) hmm.. I'll do it tonight! Well, the actual chacksum is the same, so either someone was clever enough to hack it so the checksum matched (unlikely if it's a CRC) or it's a third, perfect (for the first 256K at least) dump. Maxim

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Re: SF2 Posted: Thu Sep 21, 2000 9:00 pm
	Quote > Well, the actual chacksum is the same, so either someone was clever enough to hack it so the checksum matched (unlikely if it's a CRC) It is not really a CRC and it's not possible to find out which data has to be modifed to get it to a "good dump", unless of course there is noticable pattern which is broken somewhere.. Quote >or it's a third, perfect (for the first 256K at least) dump. I'll redump mine ASAP and see.

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Re: SF2 Posted: Mon Oct 02, 2000 10:10 pm
	Quote > I'll redump mine ASAP and see. And...? (just wondering...) Maxim

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