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Tools for floppy sector analysis #113885
09/01/18 02:51 PM
09/01/18 02:51 PM
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Al Kossow Offline OP
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What tools are available now for reverse engineering a floppy disk sector?

I imaged some rare Milwaukee Computers disks with a Supercard Pro, and the analysis part seems a bit opaque,
for example none of the controls seem to work if you bring up the histogram panel. I couldn't figure out how you tell it
to force a starting bit to decode an mfm bitstream if you don't know what the sync byte is

The other weird thing about the SCP is it wasn't obvious how to tell it the media is single-sided.

I was able to look at them with the HxC tool, but there doesn't even seem to be an MFM decoder in the track analysis panel.


Last edited by Al Kossow; 09/01/18 03:37 PM.
Re: Tools for floppy sector analysis [Re: Al Kossow] #113887
09/01/18 09:14 PM
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balrog Offline
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For graphical programs I know of DrCoolZic's Aufit utility. It's primarily Atari ST focused though.

For command line utilities, I know of two that are fairly full featured. There is Keir Fraser's Disk-Utilities, and there is Simon Owen's samdisk. Both should be able to take in SCP images and support FM and MFM decoding.

Any chance you could post the images somewhere?

Re: Tools for floppy sector analysis [Re: balrog] #113888
09/01/18 10:37 PM
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Al Kossow Offline OP
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Originally Posted by balrog

Any chance you could post the images somewhere?


sure. there isn't anything proprietary in them.

I put them under http://bitsavers.org/bits/MilwaukeeComputers

I just finished an annotated disassembly of the boot rom in http://bitsavers.org/pdf/milwaukeeComputers/firmware/MC-1200_2716_U15_MFM_6-29-82_10_Sector.txt

The sync bytes are $B1

It also appears there are no checksums in the adr or data fields

RB started on a driver for the machine, but it's been stalled trying to find disks for it.

Last edited by Al Kossow; 09/01/18 10:38 PM.
Re: Tools for floppy sector analysis [Re: Al Kossow] #113889
09/01/18 11:36 PM
09/01/18 11:36 PM
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R. Belmont Online content
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Robbert and AJR did the existing skeleton, actually, but if the images can be bunged into some MAME-compatible format I might be able to take a look. Looks like they attached a drive directly to a couple of PIAs which is rough though.

Re: Tools for floppy sector analysis [Re: R. Belmont] #113890
09/02/18 04:08 AM
09/02/18 04:08 AM
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Originally Posted by R. Belmont
Looks like they attached a drive directly to a couple of PIAs which is rough though.


Make that one PIA, one SSDA (MC6852) and a whole bunch of TTL glue attached mainly to the latter. (The other PIA just provides a Centronics interface.) The PolyMorphic Systems SSSD FDC has a very similar-looking setup (with a 8255 PPI rather than a PIA), though the schematic for that board is not available online and the Poly-8813 dump in MAME contains no useful FDC code (being likely not written for the original hardware). Motorola's AN-764 is again based around a PIA and SSDA, but with fancier support circuitry that includes dedicated PLL and CRC checker devices and a bit of RAM.

Last edited by AJR; 09/02/18 04:10 AM.
Re: Tools for floppy sector analysis [Re: Al Kossow] #113891
09/02/18 04:25 AM
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balrog Offline
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@RB we should be able to convert .scp into MFI; it's probably easiest to do so using samdisk which supports both (and I think can interface directly with SuperCardPro hardware as well).

Re: Tools for floppy sector analysis [Re: Al Kossow] #113893
09/02/18 10:01 AM
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shattered Offline
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samdisk doesn't support writing MFI, but it could be hacked to recognize this sync byte and output a sector dump.

Re: Tools for floppy sector analysis [Re: AJR] #113894
09/02/18 02:05 PM
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Al Kossow Offline OP
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Originally Posted by AJR
Originally Posted by R. Belmont
Looks like they attached a drive directly to a couple of PIAs which is rough though.


Make that one PIA, one SSDA (MC6852) and a whole bunch of TTL glue attached mainly to the latter.


The glue around the SSDA is the MFM to NRZ codec.

I finished the text translation and cleanup of the prom listing scan.

The floppy code is full of delay loops, I wondered how this possibly
work with interrupts. I put up a new scan of the schematics and looking
at it this morning noticed the system doesn't have INT or NMI hooked
up at all, they just bring it out to a 25 bin expansion port.

Don't know if the p-System just makes prom calls for I/O. It's probaby easier to try HLE at the I/O adrs to try to bootstrap
it if we can extract valid sector data. I brought my machine in to the lab to see if I can get it to boot with a copy of a
floppy made with the SCP.

This system must have been a real dog to use.

Last edited by Al Kossow; 09/02/18 02:07 PM.
Re: Tools for floppy sector analysis [Re: Al Kossow] #113899
09/03/18 03:06 AM
09/03/18 03:06 AM
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Al Kossow Offline OP
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Just made a copy of the work01 boot disk from the SCP image, took it into the lab, and it booted p-System IV !

Re: Tools for floppy sector analysis [Re: Al Kossow] #113901
09/03/18 02:44 PM
09/03/18 02:44 PM
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Al Kossow Offline OP
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I just added a bulk erased and freshly formatted scp image to the files on bitsavers.
Just the adr and data headers appear to be there

Re: Tools for floppy sector analysis [Re: shattered] #115470
06/29/19 09:48 PM
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Originally Posted by shattered
samdisk doesn't support writing MFI, but it could be hacked to recognize this sync byte and output a sector dump.


I'm working on MFI writer and A2R reader for samdisk - not submitted yet. SCP to MFI conversion (and A2R to DO, for unprotected disks) does seem to work.

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