Weird disk format

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EPTech
Posts: 6
Joined: Sun Mar 07, 2021 12:02 am

Weird disk format

Post by EPTech »

Hi all,

I recently restored a PDC Clipper for a friend of mine. It works with 3.0" floppies like CPC or PCW. I was able to get raw data from the disks using the Kryoflux hardware. The computer is based on a C64 mobo and uses a dedicated floppy drive controller to convert the floppy interface to IEC. So my first guess is that the format should be PCM DOS. I can convert the raw data to an MFM image with 1024 bytes per sector but I cannot apply this option to the PCM DOS type. The software reports an error if I do that. Is there a way to convert the raw stream or the MFM image to a D64 image?

Kind greetings,
Pascal Eraerts.
brightcaster
Posts: 369
Joined: Fri Nov 08, 2013 10:48 pm

Re: Weird disk format

Post by brightcaster »

The 3" floppy of the PDC Clipper was doublesided 500kB. So, there is no chance to get it converted to d64! The Clipper had it's own OS in proprietary roms on the c64 motherboard and in the IEC/shugart converter...

But it should be possible to connect a XU1541 to the IEC and read or write standard d64 files that way!

ftp://ftp.dreesen.ch/PDC_Clipper

Can you upload the raw stream somewhere and post a link here to have a look at it?

David
EPTech
Posts: 6
Joined: Sun Mar 07, 2021 12:02 am

Re: Weird disk format

Post by EPTech »

Thanks for your reply David,

By Double density 500kB is suppose you mean 250kB per side.
I have put a SD2IEC converter in the PDC Clipper, conveniently tugged away in the screen compartment and configured as a secondary drive (9). We can copy data from the Floppy to the SD2IEC and my friend has been able to safeguard most of his data this way. But apparently there is a disk with a lot of his programs he wrote as a kid that the floppy drive itself cannot read.

So I used the Kryoflux to make an image of that disk. I used a low density drive because this gave me the best flux signature. Using DTC I can convert to an MFM image using the settings:
start track: 1
end track: 40
sector size: 1024 bytes
sector spacing: 80 (because I used a low density drive)

If the PDC hardware can convert the MFM format from the drive into a IEC stream, I suppose there must be a way to do it in software. Hence my question if such a tool exists.

Anyway, here is an example of the raw data of one side of a partially working disk. By partially I mean the directory can be read and some programs will work.
https://www.dropbox.com/s/ws3ld9haye79s ... A.zip?dl=0

Thanks and kind greetings,
Pascal.
ZrX
Posts: 644
Joined: Tue Dec 06, 2011 9:09 pm

Re: Weird disk format

Post by ZrX »

The dump has the same data on both sides so you should flip the disk over to read the other side. As the drive only has single head KryoFlux will read the same data for both sides without flipping the disk.

But the format itself is a really weird one.

A single 1024 byte sector seems to hold 4 256 byte sectors, which are also interleaved (s1s2s3s4s1s2s3s4...), and sectors belonging to one logical track can span more than one physical track.

Edit:
After interleaving the sectors correctly, the data is almost the same as a regular d64 disk image, but larger, so typical tools can't open it.
EPTech
Posts: 6
Joined: Sun Mar 07, 2021 12:02 am

Re: Weird disk format

Post by EPTech »

Hi,

Thanks for the info.
Yes, I realized that it is only a single side and that I need to flip the disk to preserve both sides.
At least now I know that it is just a weird format and not just me making stupid settings in DTC. I still need to read up on how to interpret the Kryoflux stream format. I can try and assemble the image myself but that would be time consuming. I advised my friend to write the stream back to a blank disk and copy the data to the SD2IEC drive on the computer. I guess that is the easiest way.

I will keep you guys posted on how that goes. Thanks again,

Kind greetings,
Pascal.
EPTech
Posts: 6
Joined: Sun Mar 07, 2021 12:02 am

Re: Weird disk format

Post by EPTech »

Hi there,

I have an additional question. Since I have a somewhat tricky format that is not supported by DTC, is there a way of remastering the stream and writing it back to the same medium (3" disk)?
From reading other threads, I figured out that just writing back the stream will result in the same unreadable disk. There must be a way to optimize the stream, right? I tried to convert it to MFM but then DTC does not support writing MFM images to disks or converting them back to stream.
I have some programming skills. If I am prepared to sink time into it, does the documentation contain all I need to convert the stream files into a d64 image? In other words, does to documentation tell me all I need to know about the KF stream format?

Kind greetings,
Pascal.
brightcaster
Posts: 369
Joined: Fri Nov 08, 2013 10:48 pm

Re: Weird disk format

Post by brightcaster »

If you have a valid mfm sector dump of a known geometry you can always read that to the HxC tool and export that again as kryoflux raw stream. That (exported) raw stream will be perfectly alligned again and chances are great that written back to a floppy everything works.

https://hxc2001.com/download/floppy_dri ... r_soft.zip

But is that stream you supplied really from a floppy written by the clipper hardware? Whats the geometry of a floppy formatted by the clipper? Is it identical to the one you did send?

I say that, because the stream you did send provides only 200kB per side but all the flyers and data sheets say that it should be 250kB...
Last edited by brightcaster on Tue Apr 06, 2021 8:43 pm, edited 1 time in total.
brightcaster
Posts: 369
Joined: Fri Nov 08, 2013 10:48 pm

Re: Weird disk format

Post by brightcaster »

There is another notable anomaly! The first valid track of the raw data you provided starts with ID01 (usually ID00) and the last track is ID40 (usually ID39). But the floppy head will always start physically at track 00 whatever ID it has. So I guess it will not find anything there because that track is not formatted at all!

This oddity would result in not finding anything on the floppy. It could be solved by shifting the tracks -1 which can be done by renaming the raw files (track01.0.raw to track00.0.raw and so on till track 40.0.raw to track39.0.raw).

David
brightcaster
Posts: 369
Joined: Fri Nov 08, 2013 10:48 pm

Re: Weird disk format

Post by brightcaster »

Try writing the attached raw stream to a 3" floppy and look if the clipper can read it...

David
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Clipper.zip
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