The MTPR procedure assigns a value into a VAX internal processor
  register.

  Syntax:

     MTPR( ipr_register_expression, source_expression );

  The 'ipr_register_expression' and 'source_expression' parameters
  are  expressions  compatible  with the unsigned type.  HP Pascal
  stores the  value  specified  by  'source-expression'  into  the
  internal       processor       register       specified       by
  'ipr-register-expression'.

  The HP Pascal compiler generates user-mode code.  HP Pascal does
  not  explicitly  support the running of HP Pascal generated code
  in kernel mode.  However, if the following rules  are  observed,
  then the generated code has a good chance of working as expected
  in elevated access modes:

   o  All code must be compiled with  the  /NOCHECK  qualifier  or
      [CHECK(NONE)]  attribute.   The  HP  Pascal  for OpenVMS VAX
      systems  run-time  signaling  method  relies  on  trying  to
      execute  the HALT instruction.  In user-mode, this causes an
      exception which is  a  signal  to  the  HP  Pascal  run-time
      library.   In  kernel-mode  on  an  OpenVMS VAX system, this
      simply HALTs the machine.

   o  Avoid  all  routine  calls  which  translate  into  Run-Time
      Library  calls.   These  include  all  I/O routines, several
      arithmetic routines, several string routines, etc.