VMS Help MACRO, VAX MACRO Assembler, Instructions, MTPR  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Purpose:        Move to processor register - change
                    internal privileged registers
    Format:         opcode src.rl,procreg.rl
    Operation:      if {PSL<current-mode> NEQ 0} then {reserved
                    instruction fault}; PRS[procreg] = src
    C. Codes:       N = {dst LSS 0}, Z = {dst EQL 0}, V = 0, C = C
                    C. Codes not affected if register is not
                    replaced.
    Exceptions:     Reserved operand, privileged instruction
    Opcode:        DA    MTPR     Move to processor register
    Description:    The specified register is loaded. The second operand
                    procreg is a longword that contains the register
                    number. Execution may have register-specific side
                    effects. A reserved operand fault can occur if the
                    register does not exist. A reserved instruction fault
                    will occur if the instruction is executed in other
                    than kernel mode. See the instruction MFPR for a list
                    of processor registers.