Re: Tips for making Twiggy images

From: Natalia Portillo <claunia_at_email.domain.hidden>
Date: Mon, 02 Mar 2015 02:14:30 +0000

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Hi James,

El 22/2/15 a las 18:47, James MacPhail escribió:
>
> Sorry for this late post, I have been away.
>

>> how much can you read talking to the floppy controller, and how
>> much is really stored in the disk.

>
> The floppy disk controller in the Lisa is not an opaque black box
> as it is in some computers, it is a 6504 microprocessor with code
> in EPROM, and the commented source code is available online.
>
> It is even less opaque than the Mac, as the Lisa 1/2 don't have an
> IWM, they use a relatively simple state machine built from an
> off-the-shelf shift register, hex flip-flop, and 256 byte PROM,
> which performs the serial/parallel conversion and "bitslip FF"
> synchronization with the bitstream.
>
> The GCR translation is done entirely by the 6504 as well.
>
> As a result, there are no mysteries about the flux transitions on
> the disk, the 6504 code controls it all.

Given an opensource flux floppy reader I would lovely code anything needed to read disks.

> However, I have 1 rare twiggy disk (Lisa Basic disk 2) that has a
> crucial bad sector, and it could be that being able to read the
> flux transitions would make it practical to recreate that sector.

I've heard that is true for almost all kind of failures. Even when the head removes the magnetic material from the disk surface, that read can be used to return the digital data from the flux transitions. But this mostly mean using several heads (or cleaning them) for each track.

I have a rare (or so I've been told) Lisa COBOL disk (3.5" this one) with a bad sector, impossible to dump using DC42. I've not been able to get a DiscFerret because unless there are more than 5 interested buyers costs are prohibitively high (that's why I'm pursuing using something already usable, not like Arduino, but more like ARM MCUs or CPUs), and KryoFlux, simply not, won't give my money ever to people that call themselves computing history curators when they keep their knowledge and dumps invite-only and call their product opensource when the only source they include is an electric diagram (something even I with my novice electric engineer level can do with the board in sight) and a document about their format that's incomplete, updated, and never intended to be used, being happy to give you binary blobs for everything that really matters (the firmware and host software).

>> Free, opensource, http://github.com/claunia/DiscImageChef

>
> Thanks for that contribution!

My pleasure to give that to y'all.

Regards,
Natalia Portillo
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Received on 2015-07-16 12:39:52