Tips for Reverse Engineering a Cassette Program

[Noizer]

Yes, it seems that works even if there is a "?LOAD ERROR" but maybe will be problems in a certain condition of the game or something else who knows.

Btw I've tried to create a prg file from both original/cleaned tape but each time it will produce a prg (from $1201 to $3FFF) with different CRC32, it works but I don't trust it.

By filling memory from 1201 to 3fff with an arbitrary value before to load the TAP, you see these value inside this range 1201/3ff and not always in the same place, for me a new dump is better.

I confirm. I would call it a bad dump. A look at the extracted waves shows innumerable glitches and streches in the waveforms. It's a miracle that it even loads. Maybe you could try editing it and converting it back to Tap. I remember nippur72 doing something like that in another case.
BR

[Noizer]

Yes, it seems that works even if there is a "?LOAD ERROR" but maybe will be problems in a certain condition of the game or something else who knows.

Btw I've tried to create a prg file from both original/cleaned tape but each time it will produce a prg (from $1201 to $3FFF) with different CRC32, it works but I don't trust it.

By filling memory from 1201 to 3fff with an arbitrary value before to load the TAP, you see these value inside this range 1201/3ff and not always in the same place, for me a new dump is better.

I confirm. I would call it a bad dump. A look at the extracted waves shows innumerable glitches and streches in the waveforms. It's a miracle that it even loads. Maybe you could try editing it and converting it back to Tap. I remember

doing something like that in another case.
BR

[Vic20-Ian]

Fresh tap produced.

Boss.zip

(212.57 KiB) Downloaded 57 times

The first copy on the tape has a load error.

Fast forward to 70 on the tape counter and the second copy on the tape loads without errors.

[Mike]

I have extracted 'header.prg' and 'main.prg' from your tape and added a loader program, 'boot.prg': (download).

Decompress the *.zip archive to a directory on a SD-Card for SD2IEC or transfer the three files with their full filenames (i.e. including the '.prg' file name extension) to a disk. Then, run the file 'boot.prg'.

[kevgal]

Gday guys, here is the PRG version which requires 16k ram at blocks 1+2

Boss Chess.zip

And the Cart version (also requires 16K ram)-

Boss Chess Cart.zip

S1 to S9 set difficulty (s9 took over 2 hours to make a move!)

I think some of the issues with the tape version are due to part of the program residing in the cassette buffer.

[Mike]

I think some of the issues with the tape version are due to part of the program residing in the cassette buffer.

In my post preceding yours I just happened to provide a version of BOSS 1.5 - transferred from Vic20-Ian's tape - that addressed this issue.

[srowe]

The code in the cassette buffer is only copy protection, it's not part of the actual program.

[kevgal]

I was wondering if it was only for copy protection.
I actually used the header and the main prgs from Mike’s version to make the single PRG.
Thanks Mike.

[Mike]

I actually used the header and the main prgs from Mike’s version to make the single PRG.

Your one-file rework came at the expense that the game now needs +16K RAM to load - the original and my 3-file version are content with +8K RAM expansion. You also got the load address wrong: BASIC programs or BASIC stubs load to $1201 with +8K RAM or more, not $1200.

Regarding the first point, it should be fairly easy to use Exomizer to produce a compressed single file version that successfully loads into +8K RAM and puts both tape buffer contents and main program into place. For my part, I considered the job done by providing a proved working rip from Vic20-Ian's tape.

[kevgal]

Yep should have left out the superfluous byte at 1200, my main aim was to create a cart version for my multi carts, it would be good to squeeze it into 8k.
I’ll have to checkout this exomiser app that you mentioned.

[kevgal]

I've cheated a bit but here's a version that only needs 8k ram (still need 16k cart though unfortunately)

Boss Chess (8k).zip

[Mike]

(still need 16k cart though unfortunately)

Your latest executable should actually work with just a +8K RAM expansion. Or did you mean 8K ROM (in BLK5) and 8K RAM (in BLK1)?

I've cheated a bit [...]

The idea is good (using the screen at $1100 as temporary place for the tape buffer contents and a small routine that copies those data into the tape buffer before control is handed over to the main program) - the execution isn't. If a user modifies the bottom half of the screen before RUN, your newest version again barfs. It now also *requires* to be loaded with ",8,1".

The Right Thing™ to do was preparing a memory dump from $1100..$3FFF, with aforementioned contents and let Exomizer work on that (with -n to suppress the blinking "@" in the bottom-right corner - you don't want that to modify the screen contents either).

After I already provided a guaranteed working version of the game I am somewhat annoyed about those 'improvements' you tried. People that happen to stumble across this thread are now probably unsure about what version to download now. I am not going to repair your non-working downloads. What I provided in this post works. Period.