TP.CMD - perform a command on a 9-channel tape.

B:
   %b/manif/iocs
   status = tp.cmd( unit, cmd );

C:
   #equate tp_cmd tp.cmd
   int tp_cmd(FILE *unit,int cmd);

unit: is an open I/O unit associated with a 9-channel tape.
cmd: is a command indicating an I/O operation on the tape. Manifests for recognized commands are defined in "b/manif/iocs".
status: is the status returned by the MME GEINOS that performs the I/O operation.

TP.CMD executes an I/O command on a 9-channel tape unit.