DEBUGGER

 VAXTPU provides a debugger called TPU$DEBUG, stored in
 SYS$SHARE:TPU$DEBUG.TPU, or you can use a debug file of your own.

 To invoke VAXTPU with the debugger, use /DEBUG and optionally specify the
 debug file you want to use.  VAXTPU then executes the file containing the
 debugger before executing either TPU$INIT_PROCEDURE or the file specified
 with the /COMMAND qualifier.  For more information, see DCL HELP on
 EDIT/TPU/DEBUG.

 When you use TPU$DEBUG, VAXTPU places the debugger window on the screen.
 To set a breakpoint in the file you are debugging, press DO and issue
 debugger command SET BREAKPOINT followed by the name of the procedure
 where the breakpoint is to be set.  For example, if you wanted to set a
 breakpoint at the procedure FUM, you would issue the following command:

    SET BREAKPOINT fum

 After setting a breakpoint, use the command GO to switch control of
 execution from the debugger program to VAXTPU.  You also use the GO
 command to look at the code you are debugging before setting breakpoints.

 The screen displays the file you specified on the DCL command line, and
 EVE commands are available.  To return to the debugger so you can set
 breakpoints, use the command DEBUG at the EVE command line.

 To compile all code in the buffer, use the EVE command EXTEND ALL.  To
 execute a procedure after compilation, use the EVE command TPU.

 When VAXTPU encounters the first breakpoint in the session, the code you
 are debugging has not yet been placed in the debugger's source buffer.
 The debugger prompts for the name of the file containing your code.  Using
 your response, the debugger places your code in its source buffer.

 Once you have set breakpoints, compiled code, and started execution, you
 can use following commands for debugging:

 ATTACH [process]

    Suspends the current editing session and transfers control to another
    active process or subprocess.  (See EVE help on ATTACH.)

 CANCEL BREAKPOINT procedure-name

    Cancels a breakpoint set with the SET BREAKPOINT command.

 DEPOSIT variable := expression

    Lets you set the value of global variables, local variables, and formal
    parameters.

 DISPLAY SOURCE

    Clears text from the screen after use of the HELP or SHOW BREAKPOINTS
    command.  Causes the source display area to display your code.  By
    default, TPU$DEBUG defines CTRL/Z as DISPLAY SOURCE.

 EXAMINE variable

    Displays the current contents of global and local variables, global
    constants, formal parameters of the procedure that has been
    interrupted, and variables local to that procedure.  Local constants
    cannot be examined.

 GO

    Causes the debugger to relinquish control of execution until it is
    invoked again by a breakpoint, by the DEBUG command, or by the DEBUGON
    procedure.

 HELP

    Lists available debugger command and keypad bindings.

 QUIT

    Quits the debugger.

 SCROLL [-] number-of-lines

    Scrolls text in the source display area by the specified number of
    lines.  To scroll back through the code in the display area, use a
    negative value.  a negative number of lines.  To scroll forward by one
    line less than the number of lines in the display window, press NEXT
    SCREEN or GOLD/DOWN arrow.  To scroll back in the same way, press PREV
    SCREEN or GOLD/UP arrow.

 SET BREAKPOINT procedure-name

    Invokes the debugger when the specified procedure is executed.

    SET WINDOW top-line-number, length

    Puts the top of the debugger window at the line number specified and
    extends the window down by the second number specified.  The default
    length is 7 lines.  The minimum length is 3 lines.  The SET WINDOW
    command only changes the size of the source display area.  The output
    area and command line always occupy exactly one line.

 SHIFT [-] number-of-columns

    Moves the source display window left or right across the source code to
    display text wider than the screen.  To move left, press GOLD/LEFT
    arrow, then enter the number of columns to move.  To move right, press
    GOLD/RIGHT arrow, then enter the number of columns to move.

 SHOW BREAKPOINTS

    Lists the current breakpoints in the debugger source window.  To
    re-display code in the source window, use the DISPLAY SOURCE command.

 SPAWN [command-string]

    Suspends the current editing session and creates a subprocess.  (See
    EVE help on SPAWN.)

 STEP

    Executes one line of VAXTPU code, then returns control to the debugger.
    If you have several VAXTPU statements on one line, all statements are
    executed before control returns to the debugger.

 TPU statement

    Executes the VAXTPU statement you specify.  (See help on TPU.)

 Related Topics

    DEBUG_LINE   SET(DEBUG)