Many users run a message-trapping tool as a normal part of their working environment.

IDF sets up a dummy HNDEXT routine while it is in control, so that if a clock or other external interrupt occurs, the "DEBUG ENTERED" scenario is avoided.

If the target program sets up an HNDEXT routine, that new routine supersedes IDF's dummy handler without interfering with IDF operation. If IDF was invoked by another program that had set up a HNDEXT routine, IDF's dummy handler supersedes it.

Therefore, if you use a message-trapping tool that relies on HNDEXT processing to gain control and thus intercept messages, you should disable it before starting IDF to make sure you do not lose any messages.

Many message trappers "steal" the external new PSW and perform their own interrupt handling at that level. If the message trapper you use does this, it is likely that it can coexist with IDF. It is suggested that you test it to make sure, if you are concerned about the possibility of losing messages that arrive during a debugging session.

IDF does not affect the MSG setting, so if you do not use a message-trapping tool, none of this should affect you.