Widget image to LisaEm-compatible .dc42? from Tom Stepleton on 2018-04-09 (lisalist1)

From: Tom Stepleton <stepleton_at_email.domain.hidden>
Date: Mon, 9 Apr 2018 17:22:04 -0700 (PDT)

Hi everyone,

I'm about finished with my Widget restoration project here. I was able to backup my "spare" Widget with my UsbWidEx, then copy the image data to my
"main" Widget with BLU. My 2/10 booted and ran successfully from this
image, revealing an old Office System and Workshop installation that hadn't run for about twenty years. There was not much interesting on the disk, but it was still a nice result.

The data backup wasn't entirely smooth---during the disk's long rest, some of the sectors became harder to read. I extracted four whole-disk backups of the drive, each of which had some unreadable sectors. Next, I wrote some Python scripts to merge them together into a "combination" disk image---if a sector couldn't be read in image 1, the program would look for the sector in image 2, and so on. For any sectors that were missing from all the images, I went back to the UsbWidEx to attempt repeatedly to read them from the disk, one by one, until the Widget finally got a good read from each of them. Some of the sectors required a few dozen reads, but eventually I was able to get all of the data this way. If anyone is interested to know more about the scripts and techniques I used, feel free to drop me a line.

One of the things I had wanted to do was to convert the raw disk image recovered from the Widget into a .dc42 file that would be bootable in LisaEm. I wasn't able to succeed in this---has anyone pulled it off?

The main issue seems to have to do with sector tags. On a Widget, as the BLU manual <http://sigmasevensystems.com/blumanual.html> notes (appendix C), tag data comes at the ends of sectors. This doesn't mean that you can build a working BLU image by calling the first 512 bytes of each Widget sector
"data" and the remaining 20 bytes "tags", though. The first block---the
boot block---needs to be arranged so that LisaEm (executing the Lisa boot ROM) reads the 532-byte sector in the same order that it appears on the drive. So, for the first block, the first 20 bytes are the tag, and the remaining 512 are the data bytes. Entirely backwards from (most of? all of?) the rest of the disk.

There seem to be other differences, too. The tags don't appear to have the same format as the tags on ProFile drives---at least, not the emulated ones. From my own observations, the tag bytes seem to have been shifted around a bit. I haven't tried "unshuffling" them to match the LisaEm .dc42 arrangement, but it's something that wouldn't be too hard if you knew what to do.

But first---has anyone else out there succeeded in doing this? That is, taken a raw disk image of a Widget and created a .dc42 file that LisaEm could boot.

Thanks for any help,
--Tom

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Received on 2018-04-09 20:26:35