Dumping and Emulation Issue

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plaxamate
Posts: 15
Joined: Sat Aug 29, 2020 11:07 pm

Dumping and Emulation Issue

Post by plaxamate »

OK, so I think I've finally got this down properly. I just dumped my first early game, Ghostbusters, for the PCJr. from original disk. I dumped it and converted to PSI since I see what looks like protection on the last track. The disk is one sided, 180K and boots automatically. It was made for 128K PCJr. I've tried it on PCE, where it gets to the Activision logo and goes no further. Can someone check to make sure that the dump looks ok? It seemed OK when I dumped it. I've put the raw files along with the PSI I created here:

https://www.dropbox.com/sh/x5njrwcwbj9a ... yLU1a?dl=0

Thanks all for all the help!

Plaxamate
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mr.vince
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Joined: Tue Oct 05, 2010 5:48 pm

Re: Dumping and Emulation Issue

Post by mr.vince »

I have no experience with PC Jr. and PSI files, but does the format itself support non-standard data, violations of the recording scheme? If yes, then probably the software used for conversion does not present the scheme violations in a way expected by the program.
SomeGuy
Posts: 319
Joined: Wed Feb 18, 2015 8:18 pm

Re: Dumping and Emulation Issue

Post by SomeGuy »

PCE does not emulate a PCJr or Tandy 1000. Only a PC and XT. I believe this disk would also freeze on a genuine PC or XT because it is expecting a PCJr.

mr.vince, The PSI format used by PCE is a sector format. That means overlapping sectors are separated out in to individual sectors. The number of sectors on a track is not limited by a track length. It is very flexible and it does support some tricks, such as storing more data in a sector than is actually used, allowing a diagnostic read on that sector to return gap data and part of the next sector.

This allows some copy protections to work, but some tricker ones will not. For example if a disk writes to part of an overlapping sector with the intention of clobbering one of the sectors (to indicate the disk is used or such), that will not change the other sector and fail.

At a glance, I think this disk image is dumped OK, but I am not too familiar with any PCjr emulators that support copy protected images. (86box might?)
ZrX
Posts: 650
Joined: Tue Dec 06, 2011 9:09 pm

Re: Dumping and Emulation Issue

Post by ZrX »

The disk has invalid sector numbers, wrong sector size and a checksum error on the last track. Basic things that should work on psi and perhaps imd images.
brightcaster
Posts: 405
Joined: Fri Nov 08, 2013 10:48 pm

Re: Dumping and Emulation Issue

Post by brightcaster »

As SomeGuy said, the overlapping sectors are stored as individual sectors in the psi image. So if you write to one of them it will not change the other (in the psi image).

But you can't write to one sector on the original floppy without changing the other (at least in the overlapping area)! So it's a matter of how the protection works and what it does test. If the original floppy runs fine without a write notch, there's a good chance that the psi image works also...

BTW: The C64 Version of Ghostbusters needs to hit space bar to go beyond the intro logo! But I don't know if that's the same with the PCjr version...

David
ZrX
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Joined: Tue Dec 06, 2011 9:09 pm

Re: Dumping and Emulation Issue

Post by ZrX »

No overlapping sectors on this one. Just normal sectors but the sector headers on the last track have been altered for the purpose of copyprotection.
brightcaster
Posts: 405
Joined: Fri Nov 08, 2013 10:48 pm

Re: Dumping and Emulation Issue

Post by brightcaster »

Well, how is it called than? Sector inside sector? I see it as sector 24 with 512 byte within sector 23 with 1024 byte?

David
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ZrX
Posts: 650
Joined: Tue Dec 06, 2011 9:09 pm

Re: Dumping and Emulation Issue

Post by ZrX »

That's just because the sector header has been altered to tell you the sector is 1024 bytes while the actual sector itself is still just 512 bytes. HxC tries to interpret it according to the header information and makes it look like the next sector is inside it, which also causes the checksum to come out as bad.

Too much automation in a software isn't always a good thing.
brightcaster
Posts: 405
Joined: Fri Nov 08, 2013 10:48 pm

Re: Dumping and Emulation Issue

Post by brightcaster »

Wow, that's an interesting aspect! I agree now. Because the sectors are almost empty, the gaps as well as the synch marks can also be seen clearly in the stream view! I wondered how they have written that, because of the data artifacts at the sector borders, the floppy looks as if it has been written by a standard controller and not by a duplicator.

Yes, it's a long way to go from automatism for real KI...
plaxamate
Posts: 15
Joined: Sat Aug 29, 2020 11:07 pm

Re: Dumping and Emulation Issue

Post by plaxamate »

Very interesting! I know that there is a broken copy out there that works on DosBox, so I wasn't sure about mine.

According to this site (https://www.vogons.org/viewtopic.php?t=50664&start=40) the disk won't work at all on any CGA/EGA, etc. past the title (which is what happens on my dump), so maybe it's a good dump and I just have to wait for an emulator to come out since I can't write code. I'm curious, though, since my disk DOES have a notch in it (which I wasn't expecting). Anyone got a PCJr to check it? :-)
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