Disk version (VDK) Weetabix Vs The Titchies

Looking for a Dragon or CoCo game not already in the archive - Then request it here and hopefully it will either be uploaded to the archive or another member can upload it to this forum.
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robcfg
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by robcfg » Wed Aug 24, 2016 11:52 am

I extracted the raw binary data (not the loader but can do it also) from the cas file.

If my maths are correct, the loading address is 0x100 and the exec address is 0x302. I think this will clash with DragonDOS, maybe the code is relocatable and could be loaded in a safe memory area.

Edit:Also, I've noticed that the cas file has almost all 0x55 leader bytes removed, even on the last end block, plus there's some comment text at the end of the file. Could that be why the motor doesn't stop?

I've attached a new cas file with corrected leader bytes.
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weetarob.zip
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weetadata.zip
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robcfg
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by robcfg » Sat Aug 27, 2016 3:42 pm

More news!

I took a couple of snapshots, one with the emulator started and one once the game is loaded.

It seems that the data portion is loaded at offset 3076 (maybe 3072 as I may have not counted right the header bytes from the snapshot) and the text screen would be in the text screen memory area I guess.

You'll find attached the raw binary loader in case someone can disassemble it, and the two snapshots for reference.

I think that if we find the real exec address, we could load the text screen and the binary data from disk and then exec the game at the right address.
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SnapsAndLoader.zip
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jmk
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by jmk » Sat Aug 27, 2016 8:20 pm

An odd loader... The first block is code, which is executed at $0302. That then loads in the second block, which is a BASIC file (although it contains no valid BASIC code). It goes into $2401 (when Dragon DOS is present) or $1E01 normally.

The loader then copies that routine to $0C00 and calls $0C08. That then builds up a few tables at $7600-$7DFF, copies the rest of the code to $4000 and then starts the game by going to $65C6.

So, I have been a bit wasteful (there's a gap between $6780 and $7600) and saved out one BIN file: $4000,$7E00,$65C6.

Just do RUN"WEETABIX to start it.
weetabix.vdk.zip
Weetabix vs The Titchies VDK
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pser1
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by pser1 » Sat Aug 27, 2016 10:36 pm

Congratulations man!
You have made a great job analyzing the tape part by part and explaining us how it works.
Thanks a lot for that.

cheers
pere

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Bosco
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by Bosco » Sun Aug 28, 2016 1:18 pm

Well done James! :D

jmk
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by jmk » Sun Aug 28, 2016 3:28 pm

Thanks - have a CoCo version for completeness!

I have implemented this by doing a lot of pokes in the basic loader. It was a relatively simple conversion, it only used two common ROM calls and some other pokes were needed to cope with the different key matrix.

5E56 JSR $8012 ; Read joystick (instead of [$A00A] or $A9DE on the CoCo).
61B6 JSR $8006 ; Key read (high score) instead of [$A000] or $A1CB on the CoCo.
623C JSR $8006 ; Key read (menu) instead of [$A000] or $A1CB on the CoCo.

The keys in the original are:
Z = Left
X = Right
M = Fire
Space = Shield
F = Pause

But I had to change the pause key to P in the CoCo version because of the way the game reads the joystick (F is not returned in the bottom two bits of $FF00 on the Dragon, but it does on the CoCo, which clashes with the joystick fire buttons).
weetabix.dsk.zip
Weetabix vs The Titchies CoCo DSK
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Stig
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Re: Disk version (VDK) Weetabix Vs The Titchies

Post by Stig » Thu Sep 01, 2016 4:20 pm

Awesome !! Thanks a million for your hard work jmk :)

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