home PDP-10 TOPS-20 Commands Reference Manual Top: Chapter 2 Command description

START

Begins execution of the program in the current fork.

Format

@START (PROGRAM) location/switch

where:

location

is the octal or symbolic address where you want the program to start.

Default location - the normal starting address, that is, the first word in the program's entry vector

switch is a keyword, chosen from the list below, indicating your choice of START command options.
START Command Switches
/BACKGROUND keeps your terminal at TOPS-20 command level and starts execution of the program in a "background" fork. When the program attempts to do terminal input or output, it halts and displays the message [FORK-NAME wants the TTY].
/NORMALLY

restores your terminal to command level (if any) within the program

Default

/STAY keeps your terminal at TOPS-20 command level. Output from the program is sent to the terminal and is intermixed with whatever output is currently displayed. When the program attempts to read from the terminal, it can randomly intercept input intended for the EXEC or another program. Therefore, use this switch with programs that, once started, do not request further terminal input.

Characteristics

Starting a Noncurrent Fork

When you START a noncurrent fork, the fork becomes your current fork.

Hints

Further Information

The START command is one of the TOPS-20 multiforking-class commands. For more information about multiforking, see the section named Running Multiple Programs in the TOPS-20 User's Guide.

For more information about entry vectors, see the TOPS-20 Monitor Calls Reference Manual.

Special Cases

Running COBOL Programs a Second Time

After running a program (with a RUN or EXECUTE command, or with a GET and START or LOAD and START combination) you can usually run it again using START. COBOL programs are an exception: to run them again you must reload them.

Restrictions

Programs Competing for Terminal Input

If you use START /STAY to run a program in a background fork, either at the current or at a lower EXEC command level, (see Hints - Using PUSH to Get a New TOPS-20 Command Level, above), the program can request input from the terminal while you are giving input to the EXEC or another program. This input can be randomly intercepted by the background program when it requests terminal input. Usually though, the EXEC or the current program receives the input.

When terminal input is intercepted by the background program, the program usually types input error messages. To give input to the program, stop the program by typing two CTRL/Cs or the program's exit command. Then, if the background program is at a higher EXEC command level, give POP commands to return to the EXEC level that holds the background program. (POP terminates the current EXEC and erases programs in its memory.) Finally, give the CONTINUE /NORMALLY command; this puts you at program command level so that you can give the requested input.

Input is intercepted by the background program randomly. Therefore, you may have to type extra CTRL/Cs, program exit commands, and POPs. To reduce confusion about the direction of terminal input, it is recommended that you use START /STAY only when you plan to work at the current EXEC level while a program runs in a background fork. Use START /BACKGROUND when you plan to work at a lower EXEC level or at another program command level.

When a program started with START BACKGROUND requests terminal input, it sends the message, [FORK-NAME wants the TTY]. No input is taken by the background program until you return to program command level with CONTINUE /NORMALLY.

No I/O Control with Some Programs

Most programs read and write data to the terminal through standard input and output designators. Some programs however, use different methods of communicating with the terminal. Therefore, when you use /BACKGROUND and /STAY to control terminal input and output from a background fork, the input and output behavior of programs with nonstandard designators can be unpredictable.

Execute-only Programs

Programs that are execute-only can only be started at their normal starting address.

Related Commands

CONTINUE for resuming execution of a halted program in memory
FORK for changing the current fork
FREEZE for halting a program in a background fork
GET for placing executable programs in memory
INFORMATION FORK-STATUS for displaying the number and the status of each fork in your job
KEEP for giving a fork a kept status
LOAD for loading source or object programs into memory
REENTER for starting the program in memory at its alternate entry point (if any)
SAVE for saving a loaded program in an .EXE file
ERUN, RESET, SET NAME, SET PROGRAM, UNKEEP other multiforking-class commands for performing related functions

Examples

  1. Start the program currently in memory. 
    @START
  2. Put an executable program in memory and start it. Then run it again. 
    @GET TESTF1.EXE
@START

THIS IS A TEST.

END OF EXECUTION
CPU TIME: 0.04  ELAPSED TIME: 0.23
EXIT
@START

THIS IS A TEST.

END OF EXECUTION
CPU TIME: 0.02  ELAPSED TIME: 0.02
EXIT
  3. Begin using the FILCOM program to compare two files. Give a CTRL/C to halt FILCOM, then a CTRL/T to determine the location where it was stopped. Give the DDT command, and do some work within the DDT program; leave DDT with a CTRL/Z, returning to TOPS-20 command level. Give the START command to start FILCOM again, using as argument the address reported by CTRL/T above. 
     @FILCOM

*TTY:=DUMPER.MAC, BACKUP.MAC
^C
^T 14:49:03 FILCOM ^C from Running at 400543  Used 0:00:03.1 -
in 0:04.39, Load 2.44 in 0:01:33

@DDT
DDT
3/   PAT..+361,,3066
4/   56
^Z
@START 400543
No differences encountered
  4. Place the CLOCK program (not DIGITAL supported) in memory. KEEP the CLOCK program so that it will remain in memory when you run other programs. Then, start the CLOCK program in the background. CLOCK will display the time every half hour while you run other programs and EXEC commands. 
    @GET CLOCK.EXE
@KEEP
@START CLOCK.EXE /STAY
@
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[11:30 AM]