Hello!
After a quick glance thru the TUHS.org archives, I found a quick & dirty
hack for 4.0-Stable by Jason T. Miller <[EMAIL PROTECTED]>
The README for this thing is as follows:
>This tarball contains a dumb hack to read and write DEC RX50 diskettes
>under FreeBSD. It consists of two pieces, a kernel patch and a set of
>filters. The kernel patch, which should be applied to SYS/isa/fd.c, >adds
>the RX50 physical format to the FreeBSD floppy driver. The patch is >based
>on FreeBSD 4.0-STABLE, your mileage may vary. However, it is >conceptually
>simple and should be easy enough to apply by hand. Note that this >format
>is identical to the 5.25" 800K format, but with only one side.
>Also in the kernel/ directory is a patch for MAKEDEV which adds device
>nodes for the new format, with the name fd[n].rx50. Note that using >this
>node with a drive that is not a high-density 5.25" floppy results in a
>"device not configured" error.
>
>The filters/ directory contains two filters, rx50in and rx50out, which
>deal with the logical sector interleave performed by the RQDX >controllers
>on the PDP-11 and VAX; ideally, this would be handled in the driver; >like
>I said, this is a dumb hack. Note that the filters read or write the
>_entire_ disk; short input results in null-padding. This shouldn't be a
>big deal, but it does result in a bit of extra disk I/O. C'est la vie.
>They use standard input and standard output, and no output (except for >an
>error message on standard error) is created if the input exceeds the
>capacity of an RX50. Also keep in mind that non-PDP, non-VAX
>implementations of the RX50 used different layouts, so the filters are
>not
>appropriate, for example, for DECmate or DEC Rainbow disks. The kernel
>patch is, however, and this is the sole advantage of doing the >interleave
>in userland.
>
>EXAMPLES:
>
>Create a tar archive of 'directory' on an RX50:
> tar cf- directory/ | rx50out >/dev/fd1.rx50
>
>Extract a tar archive from an RX50:
> rx50in
>Finally, you can try to format a disk as an RX50 with
> fdformat /dev/fd1.rx50
>
>I say 'try to format' because the diskettes I format in this fashion >are
>prone to read/write errors on a real RX50. This is probably due to head
>alignment issues, but it could, of course, be something else. I've had >no
>problems reading and writing disks formatted in other ways (by DEC or
>using custom hardware, in my case a Shaffstall 6000 media conversion
>unit)
>Bear in mind that RX50s, though they are written at 96tpi and thus
>require
>a high-density drive to read and write on a PC, are _not_ a >high-density
>format, and using HD media will likely result in _lots_ of errors. I >use
>96tpi double-density media myself, but good luck finding it. The best
>substitute that is commonly available seems to be standard 360K
>double-density media without hub rings. Once again, your mileage may
>vary.
>Please send any questions or comments, bugfixes or patches to
>[EMAIL PROTECTED]; once again, this is a dumb hack, written in an
>evening, full of sound and fury, signifying nothing. The code is ugly,
>but
>the results, I'm happy to report, are not.
>
>-Jason T. Miller
> June 9, 2000
Hope this helps , Martin Heller
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