What to Do If Your Program Loops

If your program seems to be in a loop, you should first verify that it is looping, and then interrupt its processing and do one of the following:
  • Halt it entirely and return to the previous environment
  • Restart the program at an address outside of the loop.

An indication of a program loop may be what seems to be an unreasonably long processing time.

If you are in a long loop, you can use the CP TRACE command with the RUN option and look at the addresses run to identify the loop.

In a smaller loop, you can verify a loop by checking the PSW frequently. If the last word repeatedly contains the same series of addresses, it is a good indication that your program is in a loop. To check the PSW of your virtual machine, you must be in the CP command environment. You can then use DISPLAY PSW to examine the PSW by entering: 
display psw
and then enter the command BEGIN to restart the program: 
begin
If you are checking for a loop, you might enter both commands on the same line using the logical line end. If the line end is set to a pound sign (#), enter: 
display psw#begin
When you have determined that your program is in a loop, you can stop the program by entering the CMS immediate command HX: 
hx
If you want your program to continue at an address past the loop, you can use the CP command BEGIN to specify the address at which you want to continue. For example, enter: 
begin 20cd0
You could also use the CP command STORE to change the instruction address in the PSW before entering the BEGIN command. For example, enter: 
store psw 0 20cd0#begin