Programs performing full-screen I/O

Debugging programs that perform full-screen I/O is generally a difficult task, because when the debugger reaches a breakpoint, the screen image created by your program is lost. This can be extremely frustrating, since you may need to look closely at the screen image to determine whether the program is operating correctly.

IDF provides the SWAP option to make this kind of debugging easier. If MYPROG was a program that performed full-screen I/O, you could debug it with the following IDF command:

 // EXEC ASMIDF PARM='myprog (LU myterminal SWAP /Parms for MYPROG'

When the SWAP option is in effect, IDF attempts to respect the screen image created by your program. In single-step mode, IDF does nothing special. However, if you set a breakpoint in your program and press the RUN key to run the target program to that point, before turning control over to your program, IDF restores any saved screen image. Then when the breakpoint is reached, IDF captures the contents of the screen and saves it before presenting its own display. The same process occurs when you use the UNTIL command.

To capture the screen image, IDF uses the READ BUFFER command in Character Mode, so even program symbol sets should be saved.

To see the saved screen at a breakpoint, issue the SWAP command. To return to the IDF screen, just press enter.