Visualizing a C64 floppydisk

3rd Party Software, Tools & Add-ons for KryoFlux
Ze_ro
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Re: Visualizing a C64 floppydisk

Post by Ze_ro » Sun Mar 25, 2012 6:38 pm

This is really interesting. It would be neat if it could visualize other disk formats, so you could see how Amiga disks differ from Atari ST, or even Mac... or would that kind of visualization even be possible with analyzing the individual formats in much more detail?

--Zero

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DrCoolZic
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Re: Visualizing a C64 floppydisk

Post by DrCoolZic » Mon Mar 26, 2012 9:16 am

ZrX wrote:Well my G64 code is pretty manual so far, depending what kind of format it's being fed with. Some formats like bad sector protection and Vorpal tend to work with minimum work but others like Rapidlok are still pretty much a no-go.

PS. The previous Gianan Sisters image has been updated.

And some more work on the visualizing code tested with Giana Sisters and F-16 Combat Pilot showing some "data".
What is the meaning of the displayed graphics?

ZrX
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Re: Visualizing a C64 floppydisk

Post by ZrX » Wed Mar 28, 2012 6:14 am

DrCoolZic wrote:What is the meaning of the displayed graphics?
Yellow is sync part for sector 0 header if detected.
Red is sync part for the header of other sectors.
Purple is sector header.
Cyan is sync part for data.
Green is data, presented as color intensity by the value of decoded bytes, red if there's a checksum error.

F-16 Combat Pilot is interesting as even while the tracks are synced to the index, they start from random sector. There are several games like that around.

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DrCoolZic
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Re: Visualizing a C64 floppydisk

Post by DrCoolZic » Tue Feb 18, 2014 1:34 pm

This is so nice that I have implemented the same type of visualization for Atari ST
see viewtopic.php?f=7&t=769
ghost-buster-disk-data-correct-NFA.JPG
FD Data Layout with NFA (in yellow) just before index
ghost-buster-disk-data-correct-NFA.JPG (366.3 KiB) Viewed 1699 times

ZrX
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Re: Visualizing a C64 floppydisk

Post by ZrX » Wed Feb 19, 2014 7:44 am

Nice :)

How do you decide what part of the stream would classify as weak bits / NFA?

And are the sectors displayed as data or just as flux changes but with the headers and all relevant parts colored for easier identification?

My tool does visualization based of the decoded data, but can also generate flux level presentation, tho it'll be very slow due to the size of the image (about 32000 x 32000 pixels).

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DrCoolZic
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Re: Visualizing a C64 floppydisk

Post by DrCoolZic » Wed Feb 19, 2014 12:03 pm

ZrX wrote:Nice :)

How do you decide what part of the stream would classify as weak bits / NFA?

And are the sectors displayed as data or just as flux changes but with the headers and all relevant parts colored for easier identification?

My tool does visualization based of the decoded data, but can also generate flux level presentation, tho it'll be very slow due to the size of the image (about 32000 x 32000 pixels).
The visualization is also done on decoded data. So NFA (no flux area) correspond to an MFM encoding of 0 (no clock and no data transitions) which should not happen in normal case but is used for protection.
Weak bits (that I call fuzzy bits) are detected by comparing data over two revolutions if the data differs then it is considered as weak bits

in this representation data color depends of the type of records (sync, id, gap, data, ...) and the content.
This representation can be useful to see tracks with constant data but I prefer the following representation that is easier to interpret for protections
ghost-buster-disk-layout-new.JPG
ghost-buster-disk-layout-new.JPG (151.08 KiB) Viewed 1668 times
turrican-disk-layout.JPG
File with NFA spread in several track
turrican-disk-layout.JPG (157.55 KiB) Viewed 1668 times
More details about the display can be found here viewtopic.php?f=7&t=769
New version and new doc to come soon v0.3a 8-)

ZrX
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Re: Visualizing a C64 floppydisk

Post by ZrX » Thu Feb 20, 2014 7:52 am

Having no experience about Atari, I just assume NFA etc. areas are using sectors marked as bad or having bad crc here?

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DrCoolZic
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Re: Visualizing a C64 floppydisk

Post by DrCoolZic » Thu Feb 20, 2014 9:20 am

ZrX wrote:Having no experience about Atari, I just assume NFA etc. areas are using sectors marked as bad or having bad crc here?
This protection write relatively high frequency flux transition on the media. This fools the read channel that returns No transitions for long period of time (e.g. 5 ms). This is normally not possible even on unformatted areas that returns noise.

For details you can start here viewtopic.php?f=3&t=749&start=20#p6587

ZrX
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Re: Visualizing a C64 floppydisk

Post by ZrX » Thu Feb 20, 2014 11:59 am

I meant the allocated area where they've decided to place the NFA.

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DrCoolZic
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Re: Visualizing a C64 floppydisk

Post by DrCoolZic » Thu Feb 20, 2014 12:32 pm

ZrX wrote:I meant the allocated area where they've decided to place the NFA.
It is usually used with what I call sector within sector. So you have a sector that have the NFA inside. Inside this sector is located another sector that also contains the NFA this second sector is shifted by a half bitcell. This allow the FDC to read the clock bits (normally not possible with WD1772). Both sector have CRC errors and often fuzzy bits
Turrican-NFA-Zoom.JPG
Turrican-NFA-Zoom.JPG (101.11 KiB) Viewed 1648 times
Here you can see the first sector starts with an ID in yellow followed by an intra-sector gap followed by the start of a sector (orange border indicate fuzzy bits + red border indicates crc error) ...
Inside this sector (only after few bytes) we find the second sector
The NFA ( ~ 89.7 to 94 ms) is located inside the data segment of both sectors.

If you look at the decoded data read by a read track command you have the following content
turrican-nfa-track-buf.JPG
turrican-nfa-track-buf.JPG (169.07 KiB) Viewed 1648 times
The NFA is displayed in Red (clock & data = 0 i.e. MFM=0)

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