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When I was trying to edit the checksum of 3 Dragons Story for play on export consoles the graphics totally mess up. Checksum reader says everything is OK and I enter the game and this is what happens...

It's exactly the same problem on the emulator and on real hardware.

I am guessing I wrote over the actual graphics code but how am I supposed to move it to incorporate the checksum? Is this a complex thing to do also will it increase the rom beyond 32kb in size?

The Three Dragon Story bleh.png (9.04 KB)

The header area might be used for data. Here's how I'd fix it:

- Run it in Meka's debugger with the breakpoint:

b r 7ff0..7fff

- When it hits, try to figure out from the code what the start point of that data is
- Figure out the size of the data (looks like it goes right up to $7fff)
- Look for some free space in the ROM that is big enough for the data (looks like it's extremely full... the biggest I see is 18 bytes)
- Copy it there and "rewire" the addresses to point to it

If that doesn't work:

- expand the ROM to 48KB
- now you have lots of free space
- but you might not be able to use it...

Edit: Well, here's how I did it...

1.

b r 7ff0..7fff

2. Breakpoint hits at $7fdf
3. I can see it's using register HL to point at data, and the loop starts with it at $7feb. So that's where the data starts.
4.

b remove 0
w r 7ff0..7fff
j 0
c

5. I see it only reads up to $7ff2. So the block is 8 bytes.
6. Look for 8 free bytes. I see some at $0018.
7.

w clear
w 18..1f
j 0
c

8. $18 is used. There's another gap at $26-$37.
9.

w clear
w 26..37
j 0
c

10. No hits.
11. Copy 8 bytes from $7feb to $26
12. Rewire pointer at $7fdb (change from EB 7F to 26 00)
13. Add header
14. Done.

I suggest running it in Meka's debugger with

b 7ff0..7fff

and try to play through the whole game, just to check. Let us know the result.

(Irrelevant note: the bytes from $7ff5 are the ASCII "LD D,5", a remnant of source code.)

still not working :(

Hmm, I'll take a look.

Edit: I've PMed you with a link to an IPS file. I followed my own instructions and it seems to work.

Edit: attached in public now

The Three Dragon Story (KR) (BIOS fix).ips (48 B)

Author	Message
Tycho Joined: 16 Dec 2009 Posts: 243	Three Dragons Story Checksum Graphics very messy Posted: Thu Jul 29, 2010 3:32 am
Tycho Joined: 16 Dec 2009 Posts: 243	When I was trying to edit the checksum of 3 Dragons Story for play on export consoles the graphics totally mess up. Checksum reader says everything is OK and I enter the game and this is what happens... It's exactly the same problem on the emulator and on real hardware. I am guessing I wrote over the actual graphics code but how am I supposed to move it to incorporate the checksum? Is this a complex thing to do also will it increase the rom beyond 32kb in size? The Three Dragon Story bleh.png (9.04 KB)

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14752 Location: London	Posted: Thu Jul 29, 2010 8:44 am
	The header area might be used for data. Here's how I'd fix it: - Run it in Meka's debugger with the breakpoint: b r 7ff0..7fff - When it hits, try to figure out from the code what the start point of that data is - Figure out the size of the data (looks like it goes right up to $7fff) - Look for some free space in the ROM that is big enough for the data (looks like it's extremely full... the biggest I see is 18 bytes) - Copy it there and "rewire" the addresses to point to it If that doesn't work: - expand the ROM to 48KB - now you have lots of free space - but you might not be able to use it... Edit: Well, here's how I did it... 1. b r 7ff0..7fff 2. Breakpoint hits at $7fdf 3. I can see it's using register HL to point at data, and the loop starts with it at $7feb. So that's where the data starts. 4. b remove 0 w r 7ff0..7fff j 0 c 5. I see it only reads up to $7ff2. So the block is 8 bytes. 6. Look for 8 free bytes. I see some at $0018. 7. w clear w 18..1f j 0 c 8. $18 is used. There's another gap at $26-$37. 9. w clear w 26..37 j 0 c 10. No hits. 11. Copy 8 bytes from $7feb to $26 12. Rewire pointer at $7fdb (change from EB 7F to 26 00) 13. Add header 14. Done. I suggest running it in Meka's debugger with b 7ff0..7fff and try to play through the whole game, just to check. Let us know the result. (Irrelevant note: the bytes from $7ff5 are the ASCII "LD D,5", a remnant of source code.)

Tycho Joined: 16 Dec 2009 Posts: 243	Posted: Thu Jul 29, 2010 9:46 am
Tycho Joined: 16 Dec 2009 Posts: 243	still not working :(

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14752 Location: London	Posted: Thu Jul 29, 2010 12:23 pm Last edited by Maxim on Fri Jul 30, 2010 8:55 am; edited 1 time in total
	Hmm, I'll take a look. Edit: I've PMed you with a link to an IPS file. I followed my own instructions and it seems to work. Edit: attached in public now The Three Dragon Story (KR) (BIOS fix).ips (48 B)

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