Date: Tue, 9 Apr 96 21:45 WET DST From: uhclem@nemesis.lonestar.org (Frank Durda IV) To: freebsd-current%freebsd.org@rwsystr.lonestar.org Subject: Re: floppy format detection [was Re: devfs questions] Message-ID: <m0u6pu1-000CaCC@nemesis.lonestar.org>
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[5]Don't forget that even with PC-AT compatible systems, there are still [5]drives out there that have broken media-change reporting (which MS-DOS [5]conceals by assuming media change is broken on ALL drives), so the media [6]Nope, versions 4.01 and 6.22 screw up my disks by assuming the the [6]change line works on my broken 3.5in drives. [7]Yep. You need to test the change lines by looking for a media change; [7]the first time you see one that also gets change notification, you [7]set a bit in a writable store somewhere. Like userconfig does. Beg to differ. Major Japanese vendors are still selling 1.44Meg floppy drives with broken media change reporting (DC setting), and the Microsoft MS-DOS OEM kit allows computer makers to disable the check on the version of DOS they bundle with the machine. (Win '95 OPK says broken media change detection is automatic but it appears to treat it as broken until it actually gets a signal on that line, then it treats it as working.) I know this happens as I worked for PC companies that routinely disabled this flag because of the drives they bought. But you can buy 1.44Meg drives from makers with names starting with "S" or "M" that have broken media change reporting right now. You can find them in top-tier machines too from many makers. [4]Ouch. What was the type of the floppy controller? Back then it was the WD1793-02 series. Smart in some ways (stupid in others) when compared to the 765 we are stuck with today. But you could build any type of track format you wanted, and do a lot of other clever stuff. Ask a '765 to do something clever and its foot would probably fall off. [4]Asking for the disk controller to locate a sector ID that wasn't there [4]to determine the true sector count cost one second, since the controller [4]would look for the sector ID for five media revolutions before giving up. [5]It's better not to ask the controller to locate the ID if possible. For [5]nec765 and wd17xx style controllers, the best method is to use the read [5]id command. This gives you the complete format for each track. The problem with READ TRACK (READ ID only reads the ID field of the next sector to arrive under the head in WDese), you must have a buffer available the size of the largest track possible. (On a Z-80 with only 32K available for all of the drivers and their buffers, so hogging 12K for the track buffer was a problem.) Then, you must be able to locate ID fields and such in the buffer. This is made difficult by the fact that the WD part only synced on a READ TRACK on the first A1 field detected, rather than getting new sync at the start of each sector. If your motor speed deviated, parts of the track were unreadable, even with repeated readings. The TRACK READ on the 765 is a bit better in this area, but analyzing a raw track to ID media is just asking for a bad analysis. [5]I prefer using only standard formats so that format detection is [5]normally unnecessary. The problem was that ALL of those formats WERE standard! They were either the standard needed for submitting media to the IRS (3741), or the standard used by the Z80-based operating system that could be used on the same model of computer, or the standard used by CP/M systems, or the standard used by Microsoft, and so on. The customer wouldn't even know how to describe the differences (or didn't know), so complete and automatic detection was necessary. I actually have to keep a Model 16 running to use to migrate files from these old formats onto 3.5" media, which are later stored on modern archival media. I personally would like having both floppy ID mechanisms available - automatic and completely manual format selection. I would probably use the automatic until I came across the odd diskette it could not handle, and then the manual selection would come into play. TMO. Frank Durda IV <uhclem@nemesis.lonestar.org>|"If you make it go out of focus, or uhclem%nemesis@rwsystr.nkn.net | it will become clearer." - | Real live quote from "The or ...letni!rwsys!nemesis!uhclem | Manager Zone" NaNeNaNo....
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