def dpbase(opval):
    """
    Parse and return opcode,sflag,Rn,Rd for a standard
    dataprocessing instruction.
    """
    ocode = (opval >> 21) & 0xf
    sflag = (opval >> 20) & 0x1
    Rn = (opval >> 16) & 0xf
    Rd = (opval >> 12) & 0xf
    #print "DPBASE:",ocode,sflag,Rn,Rd
    return ocode,sflag,Rn,Rd