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Thread: cpmtools diskdefs for North Star MDC?

  1. #1

    Default cpmtools diskdefs for North Star MDC?

    Anyone know the correct cpmtools diskdef parameters for single density North Star MDC-A1? I'm using the Lifeboat CP/M images from deramp.com on a Sol-20.

    I guessed this one, but it doesn't quite work:

    # Northstar Micro-Disk System MDS-A1
    diskdef ns
    seclen 256
    blocksize 1024
    tracks 35
    maxdir 64
    boottrk 3
    sectrk 10
    skew 5
    os 2.2
    end

    cpmls, cpmrm, and cpmcp "work" in the sense that I can get a directory listing and add and remove files to an image, but the file data is corrupted. It could be the skew. Skew! (shakes fist...)

    On a related note, I haven't taken the time to understand the CP/M layout on a minifloppy. Any tips?

  2. #2

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    Doesn't your Northstar use hard Sectored Floppy's. If you look at the Index holes, in the cookie you will
    have more than one hole.

    I don't think you will be able to get cpmtools working on Hard Sector Floppy's.

    Larry

  3. #3

    Default

    The single density CP/M 2.2 disk images have no skew, so the cpmtools setting is probably 0 or 1. Im not familiar enough with cpmtools to know if there’s a difference between a skew of 0 and 1. I’ll be able to check a little later today.

    Now that we’re talking about the single density images, I’m curious what the skew is in the CP/M 1.4 images. I’ll check that out too.

    Mike

  4. #4

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    Yes, the disk controller uses 10 sector, hard sector disks. I have it running with Mike's VSG.

    Not sure why the DSK image would depend on hard versus soft sector, though?

    Interestingly, one problem might be maxdir. In the disk image, it looks like there's a max 56 files, not 64. cpmtools returns an error with 56, though. Works with maxdir = 32.

    Eric

  5. #5

    Default

    CP/M directory sizes are (strictly?) powers-of-two. 56 *file entries* (not the same as 56 files) does work out to 14 sectors, which won't work out to a whole number of allocation blocks, although that's not necessarily a problem. cpmtools might enforce a power-of-two directory size, regardless of whether CP/M might work.

    There might be something to be gleaned from the image file, can you point me to a specific example? I can look at it for clues about the disk layout.

    And, no, hard sectoring should have no effect on cpmtools and the disk image files.

  6. #6

    Default

    I wrote the CP/M 2.2 BIOS and created the disk images you are referring to for the North Star MDS-A1 controller. This is the older, single density controller. The BIOS is definitely configured for 64 directory entries (extents). The BIOS is here: http://deramp.com/downloads/processo...images/cpm2.2/

    Your diskdef was close, you just needed to remove the sector skew. I experimented with cpmtools this morning and it appears that a skew of 0 or 1 gives the same results. I'm assuming 0 means "no skew" which results in sectors incrementing by 1, which of course, is the same as specifying a skew of 1 which also increments by 1.

    # Northstar Single Density Micro-Disk System MDS-A1, A2, etc.
    diskdef mdsa1
    seclen 256
    blocksize 1024
    tracks 35
    maxdir 64
    boottrk 3
    sectrk 10
    skew 1
    os 2.2
    end

    It's much easier to create and modify these disk images by actually running the disk images under SIMH. I added support for the North Star single density controller to SIMH a number of years ago. I also created a custom CUTER PROM to load into SIMH that maps calls to CUTER for console I/O to the Altair ports that SIMH supports. Let me know if you want to go that route and I can help you out.

    Mike

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