Setting a breakpoint on a routine lets you move execution directly to
  the routine and inspect the local environment.

  To set a breakpoint on a routine:

  1.  Choose Browse Source from the File menu on the main window.  From
      the submenu, select All to list all modules, select Symbolic to
      list only those modules for which symbolic information is
      available.  The Browse Source dialog box appears listing your
      executable image, which is highlighted, and all the shareable
      images linked with it (for example, DEBUG and LIBRTL).  If the name
      of an image is dimmed, no symbolic information is available for
      that image.

  2.  Double click on the name of your executable image.  The names of
      the modules in that image are displayed (indented) under the image
      name.

  3.  Double click on the name of the module whose source code you want
      to display.  The names of the routines in that module are displayed
      in the Routine column.

  4.  Do one of the following:

       -  Double-click on the name of the routine on which you want to
          set a breakpoint.

       -  Click on the name of the routine and then on the Set Breakpoint
          button.

      Either of these actions sets a breakpoint at the start of the
      routine (directly after any prolog code).  In the source view, the
      toggle button to the left of the source line that contains the
      start of the routine is now filled in, confirming that the
      breakpoint is set.  (If the breakpoint view is open, the breakpoint
      will appear in the breakpoint list.  If the instruction window is
      open, the breakpoint will also display for the corresponding
      instruction.)