>>>> "Brad" == Brad Parker
<brad at heeltoe.com> writes:
Brad> [I sent this on monday but it seems to have been lost; sorry if
Brad> it's a dup]
Brad> I have a dumb question about rx01 image files used by simh.
Brad> I used "copflp" (by John Wilson - thanks John!) to image a box
Brad> of rx01 floppies.
Brad> I then put the images on pc and used simh and I can see them
Brad> fine with rt11 running under simh (i.e. "att rx0 image.dsk")
Brad> But an old program I have which will read rt11 images does not
Brad> see the directories. I am confused because it works fine with
Brad> mscp image files that I connect to simh via an ra device (like
Brad> an rd32).
Brad> What's the difference between rt11 ra image files and rt11 rx01
Brad> image files? I would think the rt11 volume and directory info
Brad> would be in the same place (but it seems I'm wrong).
Brad> I tried skipping track 0 by offsetting 128*26 bytes, but that
Brad> did not help. It looks like 128*25 might be a better offset
Brad> for floppies.
Brad> what am I missing?
Here's a guess -- I don't have the right sources at hand to make a
certain determination. Some floppies use interleaving. RX50, for
example. Looking at the RSTS RX01/02 driver, I see that it supports
interleaving; what isn't clear to me without a lot more digging is
whether that applies to RT format floppies.
If it does, then the translation looks like this:
1. Track 0 is skipped, so logical track 0 is physical track 1/
2. Within a track, logical sector numbrs 0-12 correspond to the even
numbered physical sectors, 13-25 the odd numbered physical sector. So
logical sector 13 is physical sector 1.
3. In addition to (2), sectors are skewed. After doing the
interleave calculation in (2), add 6 * logical track number to the
physical sector number to get the final value.
You might give that a try...
paul