Causing a break-in event

A "break-in event" is an event that causes IDF to break in to the target program's execution and regain control, even though no breakpoint was reached. For example, you might need to cause a break-in event if your program has gone into an infinite loop that does not contain a breakpoint.

To cause a break-in event, you need some preparation:

You need to know the address of IDF's ISA (interrupt save area). If you have not specifically set it with the ISA option when invoking IDF, the default value for the ISA location is in effect, (that is, 16 bytes at X'500').
You can cause a break-in event by obtaining the CP command prompt (typically by pressing the PA1 key), and storing any value in the first doubleword of IDF's ISA. For example: "STORE S500 00".
Do not modify the second doubleword of the ISA. Any store operation that changes the first doubleword (or any part of it) causes a break-in event at the next interrupt.

If your program has gone into an infinite loop however, there may not be any interrupts. You can ensure a steady supply of interrupts by setting the PATH option. This makes IDF take an interrupt after each target program instruction.

When a break-in event is recognized, IDF displays the IDF user interface screen and issues a message acknowledging the break-in event. You can then continue the debugging session.