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 user-area program that performed full-screen I/O, you could debug it with:

     ASMIDF myprog (SWAP /fn ft fm (abcd

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 when SWAP is in effect. 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. 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.

If you have two terminal sessions available, then you can use the LINE option. The LINE option tells IDF to use the GRAF at the specified address for its I/O, instead of using the virtual console.

A sample procedure to do this is:

     CP DEFINE GRAF xxx
     DIAL userid xxx        <-- (from the alternate session)
     ASMIDF MYPROG (LINE X'xxx'

If you use the LINE option instead of the SWAP option, your debug session is faster, because there is no need to constantly capture and re-write your program's screen.

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