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

    Purpose:        Probe accessibility - verify arguments
    Format:         opcode mode.rb,len.rw,base.ab
    Operation:      probe_mode = MAXU (mode<1:0>, PSL <PRV_MOD>);
                    condition_codes = {{accessibility of base} AND
                    {accessibilty of (base + ZEXT (len) - 1)} using
                    probe_mode}
    C. Codes:       N = 0, V = 0, C = 0,
                    Z = {if {accessible} then 0 else 1}
    Exceptions:     Translation not valid
    Opcodes:        0C    PROBER   Probe read accessibility
                    0D    PROBEW   Probe write accessibility
    Description:    The PROBE instruction checks the read or write
                    accessibility of the first and last byte specified
                    by base and the zero extended length -- the bytes
                    in between are not checked. System software must
                    check all the pages in between if they are to be
                    accessed. The protection is checked against the
                    larger of the modes specified in bits <1:0> of the
                    mode operand and the previous mode field of the PSL.
                    Note that probing with a mode operand of 0 is
                    equivalent to probing the previous mode.