'Any Kryoflux experiences made yet'
Author:Womo (guest: search)
Date: Sat, Dec 24th, 2011 @ 18:00 ( . )

Hey Pete,

when I remeber correctly to the G64 design discussions back in 1998 or so we already thought about track lengths not dividable by 8 bits exactly. I believe the discussion ended with the opinion that this can be simulated well enough by writing SYNC marks with the speed zone value increased or decreased by one step.

To my knowledge no one tested until now, if a native 1541 will ever recognise such "overspeed" or "underspeed" SYNC marks.

Furthermore, if you ever are able to detect either a weak bits zone or a write slice within a track you can easily utilise this area and either remove some of the zero bits or add some and write the resulting 0-bits area with a completely different speed zone value. This should also fix the issue.

One drawback I could think of: Protections that utilise the floppy's internal 6522 timers may be able to measure out SYNC lengths and also weak bits zones very exactly. Such checks may be able to reveal those manipulations, if not calculated very carefully. Therefore for some protections a virtual disk representation still needs to be remastered manually.

As long as all the common C64/1541 emulators are not able to parse G64 track lengths and even don't make use of the speed zone bitmaps optionally includable within a G64 along with a very precise reconstruction of the flux change data stream, all these considerations don't make much sense.


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