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Thread: FDISK "Divide Overflow" on 256MB CF Card

  1. #1
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    Default FDISK "Divide Overflow" on 256MB CF Card

    I've recently purchased and assembled an XT-IDE rev. 4 board, and am trying to use it in my 5155 (IBM PC Portable). This is my first attempt at soldering anything, so I'm not convinced that all my connections are the best, but the 5155 did boot with the card in it, and I did get to the XT-IDE Universal BIOS:

    IMG_20190104_182957.jpg

    It doesn't find a boot sector on the device, even after I have used install-mbr on Linux to create a DOS MBR, and prepped the card with a VM to include 3.31. I'm not surprised by this, as the comments on the "Modern Classic" XT-IDE walkthrough on YouTube suggested that the way to get the CF card to work was to prep it from the target PC itself.

    IMG_20190104_183017.jpg

    As far as physical disks go, I only own a set of PC-DOS 3.20 floppies, so I boot into DOS from the floppy and then attempt to use FDISK to prepare the device. This is where things go belly-up.

    IMG_20190104_183029.jpg

    I issue FDISK without any arguments, and before even getting the FDISK menu I get a "Divide Overflow" error:

    IMG_20190104_183058.jpg


    I have no idea why I shouldn't be able to prep the CF card from a virtual machine, and even less of an idea of why I can't run FDISK on it. Any pointers or help that folks could give me would be greatly appreciated.

    Video of the PC Portable booting into the XT-IDE BIOS with a different CF card in the drive: https://scitech.video/videos/watch/a...8-35774af62e68

  2. #2

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    Since you are handy with Linux, zero out the entire card with dd

    sudo dd if=/dev/zero of=/dev/sdb bs=1M

    Then try again. Replace sdb with the device address of the CF card and unmount it first.

  3. #3
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    Quote Originally Posted by pearce_jj View Post
    Since you are handy with Linux, zero out the entire card with dd

    sudo dd if=/dev/zero of=/dev/sdb bs=1M

    Then try again. Replace sdb with the device address of the CF card and unmount it first.
    No dice. I used dd with a 512b blocksize to zero the entire CF card, then I used install-mbr to build a boot sector, then a basic DOS 3.31 PC image in VirtualBox to FDISK the drive and install the system software to it with FORMAT /S and SELECT C: 001 US. I stuck the card in the 5155 and got the boot sector error, then booted with the PC-DOS 3.20 floppy and tried to FDISK it and got "Divide Overflow" again

  4. #4

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    I'd suggest blanking it with dd, then moving it directly to the PC, booting from floppy and running fdisk then format from there.

  5. #5
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    I suspect most of the problem is DOS 3.20 - 256MB is probably too large for it to deal with. 3.20 only supports 32MB maximum partition sizes although you should be able to have several partitions.

    install-mbr? No, you don't need to do that. Just set up an emulator or VM with a raw (uncompressed, no header) disk volume exactly the same size as the CF card. Then when everything is set up to your liking, just "dd" it to the CF device. You will need to make sure both your 5155 and emulated environment have the exact same CHS geometry values.

    You will want at least DOS 3.30 but that also only supports 32mb partitions maximum. As you noticed, DOS 3.31 should work excellently for this size CF as it supports partitions up to 512mb.

  6. #6
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    Quote Originally Posted by pearce_jj View Post
    I'd suggest blanking it with dd, then moving it directly to the PC, booting from floppy and running fdisk then format from there.
    I tried that when I did the dd. I used 512 byte blocks as that would blow away the MBR, but I repeated it for the entire length of the drive:

    sudo dd if=/dev/zero of=/dev/sdb bs=512 count=524288

  7. #7
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    Quote Originally Posted by SomeGuy View Post
    I suspect most of the problem is DOS 3.20 - 256MB is probably too large for it to deal with. 3.20 only supports 32MB maximum partition sizes although you should be able to have several partitions.

    install-mbr? No, you don't need to do that. Just set up an emulator or VM with a raw (uncompressed, no header) disk volume exactly the same size as the CF card. Then when everything is set up to your liking, just "dd" it to the CF device. You will need to make sure both your 5155 and emulated environment have the exact same CHS geometry values.

    You will want at least DOS 3.30 but that also only supports 32mb partitions maximum. As you noticed, DOS 3.31 should work excellently for this size CF as it supports partitions up to 512mb.
    What I'll try next is seeing if I can use fdisk on it from a VM running DOS 3.20. I think I tried that in the past and it worked, which would confuse me because if the problem is fdisk then it should be a problem whether run from the VM or run from the actual 5155.

  8. #8
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    Quote Originally Posted by djfitzgerald View Post
    What I'll try next is seeing if I can use fdisk on it from a VM running DOS 3.20. I think I tried that in the past and it worked, which would confuse me because if the problem is fdisk then it should be a problem whether run from the VM or run from the actual 5155.
    Okay, so I did this yesterday, and FDISK worked fine on the CF card from a VirtualBox image (I have VirtualBox running on Linux, and configured so that the block device at /dev/sdb/ is passed through to a *.VMDK file that is mounted as a disk image for an IDE device). Not only that, but I can actually boot my VM from the CF card, using it as an IDE disk.

    I'm wondering if my soldering of one or more of the IDE connector's 40 pins is bad, or if my CF reader is borked. I know that with XT-IDE offline, I can run FDISK on the PC and have it yell at me that there are no fixed disks, which is good.

    One other thing I am concerned about. If you look at the images in my first post to the thread, you will see that my CF card capacity is listed as 8064.0 MiB / 0.4 kiB. Thats not accurate, as its a 256MB CF card. I tried with a 2GB CF card and got the same capacity listed. I'm assuming that the listed capacity of "8064.0 MiB / 0.4 kiB" is the maximum that the XT-IDE BIOS can recognize, but am wondering if the fact that its not listing my actual CF card capacity is a sign of a problem.

  9. #9
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    Another data point: Remember that SD card I prepared with a virtual machine to boot into DOS 3.30? I plugged it into an old ThinkPad X41 and turned the laptop on... the machine booted into DOS 3.30 from the CF card. So I think this whole "No boot sector found" business from XT-IDE is bunk.

  10. #10

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    Try upgrading to a newer revision of the XUB that uses the new drive translation code, Try r591, The 'No boot sector found' error is likely because you are not configuring the CF on the 5155 with the 1.1.5 XUB, Using another computer to configure the CF for the 5155 that is running 1.1.5 XUB is asking for trouble.

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