Pertinent to this topic, there's currently a discussion on the LisaList regarding making Twiggy disk images. Some comments from James McPhail from SigmaSeven Systems, creator of X/Profile and BLU. The initial Lisa 2/MacXL conversions with 400k drives had a "LisaLite" board that sat between the Lisa I/O board and the 400K floppy, I assume to translate between the Twiggy implementation and the 400k drive protocol.
Later machines did away with the LisaLite board, but I'll admit I don't know how - perhaps that's the IWM in the Lisa 2/10 as referred to above.
--
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.
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.
>Free, opensource, http://github.com/claunia/DiscImageChef
Thanks for that contribution!
Later machines did away with the LisaLite board, but I'll admit I don't know how - perhaps that's the IWM in the Lisa 2/10 as referred to above.
--
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.
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.
>Free, opensource, http://github.com/claunia/DiscImageChef
Thanks for that contribution!