Problem reading side 1 of a 360k PC disk

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NRS
Posts: 27
Joined: Mon May 06, 2013 8:32 pm

Re: Problem reading side 1 of a 360k PC disk

Post by NRS »

So which part (DOS/BIOS/Controller) decides how that line should be set during normal PC/DOS operation (when the disk works on both sides without a hitch)? I find it hard to believe that DOS or the BIOS switch between one value for side 0, and another for side 1.

Remember that specifying -dd1 works for BOTH sides, and -dd0 works for NEITHER side in DTC, and not specifying -dd at all reads the first but not the second side properly. I'm getting the feeling that it's DTC that acts weirdly when no value is specified, not the drive or the disk. How does DTC know how to set the drive density line? I have read both 360K and 1.2M disks successfully without ever specifying that option, so it can't be that it just defaults to 0, as the documentation claims. If DTC uses information from the boot sector when using image type -i4 to select the density, then that would be the answer to the question why these particular two disks cause problems: because KQ2 (Tandy Version) is the first game I have imaged that does not have a standard DOS boot sector, being a self-booting game.

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IFW
Posts: 3079
Joined: Mon Nov 08, 2010 2:42 pm

Re: Problem reading side 1 of a 360k PC disk

Post by IFW »

1, Yes, it defaults to 0 - you can see this via device level logging
2, The BIOS is unlikely to set it; unless if you can select the drive type (but ultimately it's the FDC pulling the line). If it sets anything at all, it's a hardwired value, but see (4)
3, DTC does not do disk analysis (at least not in the sense you imply), hence the content is irrelevant during read
4, It is simply not possible to determine a correct default value for this line as it is drive dependent, and some drives actually allow to change the behaviour of the line (active low/high) via a jumper... so if it works as a default setting the drive was probably used in a PC before and jumpered correctly for that.

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karadoc
Posts: 139
Joined: Sun Oct 31, 2010 9:12 pm

Re: Problem reading side 1 of a 360k PC disk

Post by karadoc »

Yes, this does need to be added to the GUI. I'm working on some secure hashing features at the moment, and I have some other things to catch up on, but I will add this to the list of things to be done. Thanks for bringing it to my attention.

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