You can also issue CP commands. To return to edit mode, you use
the special CMS subset command, RETURN. If you enter the Immediate
command HX, your editing session is terminated abnormally and your
virtual machine is returned to the CMS environment. When you are finished with an edit session, you return to the CMS environment by issuing the FILE subcommand, which indicates that all
modifications or data insertions that you have made should be written
onto a CMS disk, or by issuing the subcommand QUIT, which tells the
editor not to save any modifications or insertions made since the
last time the file was written.
More detailed information about EDIT subcommands and how
the CMS editor is contained in this publication in "section CMS Editor" and in the DEBUG to use
5. The CMS DEBUG is a special CMS facility that provides subcommands to help
you debug programs at your terminal. Your virtual machine enters the
debug environment when you issue the CMS command:
debug You may want to enter this command after you have loaded a program
into storage and before you begin executing it. At this time you can
set "breakpoints," or address stops, where you wish to halt your
program's execution so that you can examine and change the contents
of general registers and storage areas. When these breakpoints are
encountered, your machine is placed in the debug environment. You can also enter the debug environment by issuing the CP EXTERNAL command, which causes an external interrupt to your virtual machine. Valid DEBUG subcommands that you can enter in this environment
are:
BREAK CAW CSW DEFINE DUMP GO GPR HX ORIGIN PSW RETURN SET STORE X You can also use the ICP function in the debug environment to enter CP commands. You leave the debug environment in any of the following ways: If the program you are running completes execution, you are returned
to the CMS environment. If your virtual machine entered the debug environment after a
breakpoint was encountered, it returns to CMS when you issue the DEBUG subcommand:
hx
To continue the execution of your program, you use the DEBUG subcommand:
go 20 IBM VM/370 CMS User's Guide
Pg. of GC20-1819-2 Rev March 30, 1979 by Supp. SD23-9024-1 for 5748-XX8 If your virtual machine is in the debug environment and is not
executing a program, the DEBUG subcommand:
return
returns it to the CMS environment. CMS/DOS If you are a DOS/VSE user, the CMS/DOS environment provides you with all
the CMS interactive functions and facilities, as well as special CMS/DOS commands which simulate DOS functions. The CMS/DOS environment becomes
active when you issue the command:
set dos on When your virtual machine is in the CMSjDOS environment you can issue
any command line that would be valid in the CMS environment, including
the facilities of EDIT, DEBUG, and EXEC, but excluding CMS commands or
program modules that load and/or execute programs that use OS macros or
functions.
The following commands are provided in CMS/DOS to test and develop DOS programs, and to provide access to DOS/iS libraries: ASSGN DLBL DOSLIB DOSLKED DOSPLI DSERV ESERV FETCH FCOBOL LISTIO OPTION PSERV RSERV SSERi Your virtual machine leaves the CMSjDOS environment when you issue the
command:
set dos off
If you reload CMS (with an IPL command) during a terminal session, you
must also reissue the SET DOS ON command.
Interrupting Program Execution When you are executing a program under CMS or executing a CMS command,
your virtual machine is not available for you to enter commands. There
are, however, ways in which you can interrupt a program and halt its
execution, either temporarily, in which case you can resume its
execution, or permanently, in which case your virtual machine returns to
the CMS environment. In both cases, you interrupt execution by creating
an "attention interruption," which may take two forms: An attention interruption to your virtual machine operating systea An attention interruption to the control program
These situaticns result in what are known as virtual machine (VM) or
control program (CP) "reads" being presented tc your virtual console. On a typewriter terminal, the keyboard unlocks when a read occurs. Section 2. VM/370 Environments and Mode switching 21
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