[Simh] Error with tape file marks on PDP-11 TU77 / Ultrix 3.1 "dd"

[Jörg Hoppe]

Hello,

While trying to install Ultrix-11 V3.1, I ran into a problem with
tape control: The /.setup/setup_osl tool can not access tape files
to install optional software.

Some facts:
 - A source code review shows that setup_osl internally issues a
  "dd if=/dev/nrht0 of=/dev/null bs=20b files=<n>"
  to position the tape to file <n>. This fails, the tape is read until 
the end.
- The error can be reproduced by issuing a "dd" (see below)
- The tape image has file marks, as simhtools\mtdump.exe shows.
- The Ultrix magnetic tape tool "mt" CAN skip files.
 "mt rewind" and "mt fsf <n>" work fine.
- The error occurs also with the well known Ultrix-11 V2 boot tape
http://www.bitsavers.org/bits/DEC/pdp11/magtapes/ultrix-11/BB-X302B-BC_ULTRIX-11_V2_16USR_BIN_1984.tap
- I've limited knowledge regarding this tape image stuff ....

kind regards
J. Hoppe



------ tape configuration under SimH ------------------
sim> ;the ultrix boot tape  requires a TU77!
sim> SET TU ENABLED
sim> SET TU TM03
sim> SET TU0 TU77
sim> ATT TU0 bootape2\BB-X302B-BC_ULTRIX-11_V2_16USR_BIN_1984.tap


------- Output under Ultrix-11 3.1 ---------------------
ccg53# mt rewind
ccg53# dd if=/dev/nrht0 of=/dev/null bs=20b files=5
read: Fatal error - tape position lost
1692+0 records in
1692+0 records out
ccg53#



----------- SimH TU Debug output ----------------
...
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13524064
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13524064
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13534312
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13534312
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13544560
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13544560
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13554808
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13554808
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13565056
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13565056
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13575304
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13575304
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13585552
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13585552
 >>TU0 DONE: fnc=READF, fc=024000, fs=010640, er=000000, pos=13595800
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13595800
 >>TU0 DONE: fnc=READF, fc=000000, fs=150644, er=001000, pos=13595804
 >>TU0 STRT: fnc=FCLR, fc=000000, fs=010640, er=000000, pos=13595804
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13595804
 >>TU0 DONE: fnc=READF, fc=000000, fs=150644, er=001000, pos=13595808
 >>TU0 STRT: fnc=FCLR, fc=000000, fs=010640, er=000000, pos=13595808
 >>TU0 STRT: fnc=READF, fc=154000, fs=010640, er=000000, pos=13595808
 >>TU0 DONE: fnc=READF, fc=000000, fs=150640, er=020000, pos=13595808
 >>TU0 STRT: fnc=FCLR, fc=000000, fs=010640, er=000000, pos=13595808