multibank binaries - checksum

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tvrfan
Tuning Addict
Posts: 349
Joined: Sat May 14, 2011 11:41 pm
Location: New Zealand

multibank binaries - checksum

Post by tvrfan » Sat Jun 09, 2018 2:55 pm

To any long time experts out there -

Do you know if the multibanks do a checksum or not ?

Does it do one for each bank ?

The checksum obvious for single banks like A9L, but I'm looking at BWAK3N2 (which appears to use the secondary stack R22 as the background task pointer?) and I can't see how or where it does any checksum. SAD doesn't work much at all for BWAK3N2 so I need to add more functionality, which doesn't help....

Any help or info on this appreciated - thanks
TVR, Triumph (cars), kit cars, classics. Ex IT geek, development and databases.

https://github.com/tvrfan/EEC-IV-disassembler

sailorbob
BIN Hacker
Posts: 1649
Joined: Tue Jul 12, 2005 6:10 am

Re: multibank binaries - checksum

Post by sailorbob » Wed Jun 13, 2018 2:15 am

The multiple bank checksum calculation is the same as single bank checksum with each bank being added in turn. In the BWAK3 strategy the routine is at 0x872D9.

tvrfan
Tuning Addict
Posts: 349
Joined: Sat May 14, 2011 11:41 pm
Location: New Zealand

Re: multibank binaries - checksum

Post by tvrfan » Wed Jun 13, 2018 2:50 pm

Thanks Bob, will check that out....

[2 mins later ]

Damn, I should have spotted that....Now you pointed that out, it's quite obvious.
Interesting that the routine stops at a slightly different end address for each bank....
TVR, Triumph (cars), kit cars, classics. Ex IT geek, development and databases.

https://github.com/tvrfan/EEC-IV-disassembler

sailorbob
BIN Hacker
Posts: 1649
Joined: Tue Jul 12, 2005 6:10 am

Re: multibank binaries - checksum

Post by sailorbob » Wed Jun 13, 2018 3:30 pm

No point in checksumming unused areas of ROM and, IIRC, the VID block is excluded.

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