In this episode, my goal is to remaster a Commodore DOS 1 demo disk. This isn’t easy because:

  • the DOS 1 disk format has a different layout (tracks/sectors) than a DOS 2 disk
  • OpenCBM doesn’t work very well with DOS 1 units, or those with 2 disk drives
  • there doesn’t seem to be an original image available.

I spend much of my time digging through the OpenCBM source code and enhancing it to support my DOS 1 2040, and do eventually get a DOS 1 demo disk written and succeed in running a (passing) performance test on my 2040 with my PET. However I fell back to using the 4040 demo disk contents, written to a DOS 1 format disk formatted by my 2040.

The playlist with other videos of me working on this 2040 is here: https://www.youtube.com/playlist?list=PLXs34HaWLi10C6ZdFEMkyiR1x8duq9cft

Timestamps

00:00 Intro
01:53 OpenCBM 2040 identification
24:15 DOS 1 OpenCBM status handling
34:35 OpenCBM dual drive directory listing
37:52 2040 demo disk images
58:46 Testing with my PET
63:58 Wrap-up

Problems hit:

  • OpenCBM didn’t correctly identify a DOS 1 2040 disk drive - I enhanced the source code to use a Memory Read (M-R) command that is compatible with both DOS 1 and DOS 2 drives.
  • OpenCBM didn’t properly report the status of a DOS 1 2040 disk drive - I enhanced the source code to handle both DOS 1 and DOS 2 status reporting.
  • OpenCBM cbmcopy/cbmwrite doesn’t properly write files to a DOS 1 2040 drive. I have not diagnosed this problem - instead I worked around this as below.
  • The “2040 demo disk” d64 on zimmers.net is actually a DOS 2 4040 demo disk, not a 2040 disk. I wrote this image to my DOS 2 2031 drive and copied the files over to a DOS 1 formatted disk, using my PET with both the 2040 and 2031 connected.
  • The 2040 demo disk in lynx (LNX) format, is not a list of original files - it also contains some games, and what look like some personal files. I unlynxed this using cbmconvert 2.1, but didn’t end up using the image.

You can find my fork of OpenCBM, with the fixes I made, here: https://github.com/piersfinlayson/OpenCBM
The 4040 demo disk labelled as 2040 demo disk is here: http://www.zimmers.net/anonftp/pub/cbm/demodisks/drives/2040-demo.d64.gz
The lynxed 2040 demo disk files are here: http://www.zimmers.net/anonftp/pub/cbm/demodisks/drives/2040DEMO.LNX.ZIP
cbmconvert is here: http://www.zimmers.net/anonftp/pub/cbm/crossplatform/converters/unix/cbmconvert-2.1.2.tar.gz

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