a8cas-convert and FSK blocks

[smesgr]

Hi everybody,

 

i start playing around with backup of some (personal/family) tapes i have. I started to backup some tapes which have a known good dump and compare my dumps against them.

 

A) Silent Service - prone to not loading on the real thing. Had some bad blocks but with audacity I could fix a cracking sound in one of the data blocks which led to a fsk block and bad data detection by a8cas. Plus had alot of other FSK-blocks. I did trim down the leading and tailing sound and those blocks disappear. Except some magic bytes (checksum?) - it is a 1:1 copy

B) Escape from Traam - does not work on the real thing. Had again some fsk-blocks which could be mostly get rid of if the tailing and leading audio was cut. Again some repeating byte differs in a regular pattern. First data-block had a different irq_length after changing the value to a higher number (or copy the value from the good dump) the dump started to work - I'm a bit confused why this happens but maybe a question for another topic

C) BMX simulator - this tape has several sections thus again alot of fsk-blocks compared to the good dump. Otherwise it seems to be nearly identical.

 

so my question is it possible to filter those blocks in the dump using a8cas or another tool? As far as I understood those blocks are for copy protection stuff something those specific tapes should afaik not have.

[baktra]

The a8cas-convert creates the fsk blocks whenever it detects a signal that doesn't constitute a regular data block. It can just be a noise, or it can be part of some copy protection scheme.

 

To remove the fsk blocks, you can use for example TURGEN and its Tape Image Extractor function. That function allows you to display the contents of the tape image, select a subset of tape image chunks, and save them as a new, clean tape image.

 

Another possibility is to use a8cas-convert to convert the .cas file to a .hex file. You can then edit the .hex file with a text editor, remove the fsk chunks and re-convert to a .cas file.

[smesgr]

cool this works fine. After removing those blocks BMX simulator had now 2 bytes less than the good dump. Opening good dump with TURGEN I could see a 134 byte block which seems to be odd. Maybe a wrong byte recording which is ignored/skipped by the Atari. Otherwise it seems to be identical and both dumps work fine.

 

Great thanks

Edited May 23, 2023 by smesgr

[Rybags]

Does the program actually use a long or errored block?

A normal block has 2 speed measurement, control byte, payload (128) and checksum for a total of 132 bytes.

 

[smesgr]

it is at the beginning, after the loading screen. So I doubt it is necessary. Even after playing both dumps i couldn't spot a difference.

Edited May 27, 2023 by smesgr