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

    Purpose:        Save processor context - save register and
                    memory management context
    Format:         opcode
    Operation:      if PSL<current-mode> NEQU 0 then {opcode reserved

                    to Digital fault}; {save process general registers
                    in the process control block}; {remove PSL and PC
                    from stack and save in PCB}; {switch to interrupt
                    stack}
    C. Codes:       Not affected
    Exceptions:     Reserved operand, privileged instruction
    Opcodes:        07    SVPCTX   Load process context
    Description:    The process control block is specified by the
                    internal processor register PCBB (process control
                    block base). The general registers are saved in
                    the PCB. If the current stack in use is the kernel
                    stack, execution is changed to the interrupt
                    stack.