ADSTOP                                                   CP Privilege Class:  G

Use the ADSTOP command to halt the execution of a virtual machine at a virtual
instruction address.  Execution halts when the instruction at the address
specified in the command is the next instruction to be executed.  Only one
ADSTOP command can be in effect at a given time.  If a second ADSTOP command is
issued, the previous ADSTOP setting is canceled.  The format of the ADSTOP
command is:
+----------+------------------------------------------------------------------+
| ADSTOP   | hexloc|OFF                                                       |
+----------+------------------------------------------------------------------+
where:

hexloc   is the 6-character hexadecimal representation of the virtual
         instruction address where execution is to be halted.

OFF      cancels any previous ADSTOP setting.


Usage Notes:

1.  When execution halts, the CP command mode is entered and a message is
    displayed.  At this point, you may invoke other CP debugging commands.
    To resume operation of the virtual machine, issue the BEGIN command.  Once
    an ADSTOP location is set, it is removed (turned off) by the following:
    o   Reaching the virtual storage location specified in the ADSTOP command.
    o   Performing a virtual IPL or SYSTEM RESET.
    o   Issuing the ADSTOP OFF command.
    o   Specifying a different location with a new ADSTOP hexloc command.

2.  Since the ADSTOP function modifies storage by placing a CP SVC X'B3' at the
    specified location, you should not:
    o   Designate an address within a shared segment.  If a shared segment is
        modified by an ADSTOP command, a warning message is issued to the user
        and the virtual machine is unshared from (given a private copy of) the
        named system.  Other users of the segment continue to operate with an
        unchanged copy of that segment.
    o   Use the TRACE command with the INSTRUCT, BRANCH, or ALL operands when a
        traced instruction is located at the ADSTOP address.

3.  Address stop (ADSTOP hexloc) is specified as a 6-character virtual machine
    real address.  For OS/VS or DOS/VS, the specified address must be in fixed
    storage.  Movement of the page containing the ADSTOP can cause erroneous
    processing because the resulting SVC X'B3' is presented to the virtual
    machine for handling.

4.  If the SVC handling portion of the virtual machine assist feature is
    enabled on your virtual machine, CP turns it off when an ADSTOP is set.
    When the address stop is removed, CP returns the assist feature SVC
    handling to its previous status.

Response:

ADSTOP AT xxxxxx
   The instruction whose address is xxxxxx is the next instruction scheduled
   for execution.  The virtual machine is in a stopped state.  Any CP command
   (including an ADSTOP command to set the next address stop) can be issued.
   Enter the CP command BEGIN to resume execution at the instruction location
   xxxxxx, or at any other location desired.