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Thread: DOS File Level access to Secondary (370H) FDC - Driver

  1. #51

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    I thought the DPB in boot sector started with DOS 2? I'll dig up some 8 SPT minis and play around

  2. #52
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    It did, but wasn't universally followed by third-party vendors. (DOS 2.x still had a fair number "almost PC" vendors)

  3. #53

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    Yeah so it doesn't look like it was so much an issue of support being dropped as it is they've always done that silly "sector size on boot limit" thing. Even DOS 2.11 balks at a BPB from the driver with 1024 byte sectors.

    Really makes me wonder if there is a viable way to hack it after boot time. Not because blocking/deblocking is hard, but because this would be cooler.

    IMG_20200412_180540054.jpg
    IMG_20200412_182818983.jpg

  4. #54

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    Quote Originally Posted by maxtherabbit View Post
    Yeah so it doesn't look like it was so much an issue of support being dropped as it is they've always done that silly "sector size on boot limit" thing. Even DOS 2.11 balks at a BPB from the driver with 1024 byte sectors.

    Really makes me wonder if there is a viable way to hack it after boot time. Not because blocking/deblocking is hard, but because this would be cooler.
    Damn you Microsoft! LOL!
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  5. #55

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    How does the PC BIOS determine if you are using a 360kB disk in a 1.2MB drive to boot even? Does it just start at 500kHz and reduce the rate if it doesn't get a good read?

  6. #56
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    It's all in the BIOS. Take a look at the AT BIOS code--a READ ID is performed which tells everything. Incidental to that is that the BIOS makes the determination to double-step, not DOS.

  7. #57
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    Quote Originally Posted by maxtherabbit View Post
    Yeah so it doesn't look like it was so much an issue of support being dropped as it is they've always done that silly "sector size on boot limit" thing. Even DOS 2.11 balks at a BPB from the driver with 1024 byte sectors.

    Really makes me wonder if there is a viable way to hack it after boot time. Not because blocking/deblocking is hard, but because this would be cooler.
    You could hack the msinit routine to always use 1024 bytes as maxsect, but that has unfortunate consequences, such as doubling the storage required for BUFFERS, etc. I suspect that SMARTDRV would also need to double buffer size as well.

  8. #58

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    Quote Originally Posted by Chuck(G) View Post
    It's all in the BIOS. Take a look at the AT BIOS code--a READ ID is performed which tells everything. Incidental to that is that the BIOS makes the determination to double-step, not DOS.
    didn't realise the AT BIOS source was available, but I found it and it does in fact cycle through the data rates in the retry function called by the main R/W/V function unless the media determined bit is set in the drive state memory variable, in which case it reports true error

    after a successful operation it sets the bit

  9. #59
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    One way to handle 5.25" 720K floppies on the 5170 was to reset the "double step" BIOS flag (0:90h/0:91h, IIRC) using a small TSR. Some later/third party BIOSes redefined the flags, so it didn't work on all systems.

  10. #60

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    Finally located a double sided TM848E and it's on the way. Assuming it arrives safely I'll resume work on the DSDD 8" profile immediately

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