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Thread: TRS-80 Model 12 successfully shipped

  1. #21
    Join Date
    Jun 2013
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    Sydney, OZ
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    137

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    Quote Originally Posted by Alphasite View Post
    I couldn't get CP/M on the Model II to format. Did you use the stock firmware on your HxC?
    Yep - stock early HD boot rom.
    It's been a while and the details are fuzzy but I'm sure I had to alter the header for mixed density. Same goes for the Model I with a SD trk 0.
    This PDF explains the layout of the HFE header

    http://hxc2001.com/download/floppy_d...ile_format.pdf

  2. #22

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    Quote Originally Posted by lowen View Post
    Yes, a bootable Model II disk has an FM track 0, with 128 byte sectors. This is so that the boot ROM can boot from floppy without using DMA, which on the II is required for MFM transfers (a 4MHz Z80 as implemented in the II was not considered to be fast enough to pull in MFM data in programmed-I/O mode; what's funny is that the Model III does do this with a 2MHz Z80 at the half data rate of the 5.25 DD drive system, although it gets done by using NMI to do it in most of the TRS-80 DOSes).

    I found this out first-hand while single-stepping through the boot while troubleshooting the MESS/MAME WD17xx floppy controller emulation bug for deleted data address marks, so I've actually stepped through the boot ROM code as well as what the boot ROM pulls in from track 0.

    A data disk does not have this issue.

    The code to do this is in the LS-DOS 6.2 source archive that I've posted before, in the BACKUP/CMD sources. If the backup is creating a system disk, then track 0 gets reformatted FM 128 bytes per sector. So even on a data disk track 0 is reserved for BOOT/SYS.

    People who have cut their floppy system teeth on the 765-style controllers seem to have a difficult time realizing that the WD1791/1793/2793 controllers can switch from MFM to and from FM on the fly while data is under the head even during a write track (format) command; this was done for dual-booting Model I/III games, for instance. The IMD format doesn't support these; DMK does, though, as would actual flux-level archives like the Kryoflux extracts. I'm not sure the HxC is capable of handling that kind of mixed density; it would be nice, though. And while I have a couple of Model 12 mainboards and parts enough to put together a 12 sans disks, my HxC is hooked up to my CPU280 at the moment..... need to get another HxC, maybe one day.
    It is supposedly possible to handle mixed if the image is prepared for it and that requires some XML work. I'll test a few theories I have with mixed density on a Model I using premade images.

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