The README.md says:
mtdump Dump the record structure of a SIMH, E11, TPC, or P7B
and:
simtools/extracters/mtdump/mtdump.txt
also talks about processing P7B files, but the code doesn't handle such files
or a -p option, at all. That needs to be fixed in the documentation.
Looking at mtdump.c, I can see that files in P7B format don't fit well in the code,
as I think all of the other formats use a header that gives the record length, but P7B
(aka Paul Pierce format) don't have any headers or trailers, just a stream of
bytes with 6-bit char codes, a parity bit, and a 'new record starting' bit, plus
a special byte value (0x8F) to signify a tape mark.