[Simh] PDP-11 Mag Tapes

[B M]

I am using SIMH with some mag tape images (TM device) under DOS-11 in the
PDP-11 simulator.

Several of the tape images do not work.  DOS-11 doesn't seem to process the
file correctly.
Executing 'MT0:/DI' in PIP under DOS-11 frequently fails with an error code
(eg. S257), or
does not have all files listed.

The format of the tape images is as follows:
      <label><record1>...<recordN><eof>                           file #1
                 ...
      <label><record1>...<recordN><eof>                           file #x
      <eof>
      <eof>

The <label> record is a DOS-11 file entry (filename in RAD-50, ...) and is
14 bytes long.

Each of the data records has a 4 byte record length at the beginning and end
of the
record.  The length is a 4 byte integer in little endian form.  A 512 byte
record ends
up being 512 bytes + 2 x 4 bytes or 520 bytes in total.

An <eof> is 0x00000000 (4 x 0 bytes).

End of data is 2 <eof> back to back.

I have written a program that verifies the content of the tape image.  I see
the expected content of
files under my verification program, but the content frequently does not
match what DOS-11 gets.

I am looking for suggestions on how to tackle this problem.  I have several
800bpi 9-track tapes which
contain DEC source code for really early versions of RSTS, RT-11, etc.  I am
looking to image the files
and make them available for SIMH.

I can supply copies of the tape images as necessary.  Note that I am using
40 year old equipment
to retrieve the tape images.  The tapes are being read correctly without
read errors popping up.

Is anyone interested in RSTS or RT-11 for really early PDP-11's such as
PDP-11/20 or PDP-11/10??
I am trying to get the early versions of various OS'  running on my
PDP-11/10 and PDP-11/20.
Eventually I also want to get Unix running on my PDP-11/20 (just for the
geek factor!!)

Thanks!

--barrym
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