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Written By Alan Wagstaff


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Acetrace

Alan Wagstaff, Richmond, North Yorkshire

Here are two assembly-language programs for the BBC Micro. They can come in very handy when faced with bugs in long Basic programs.

The Trace facility on the BBC Micro is useful but there are occasions when one is left gazing at a screenful of line numbers, obscuring the program display and leaving one feeling a triple non-plussed.

Acetrace displays the Basic line number which is about to be executed in the top left hand corner of the screen. There is then a pause for about 2.5 seconds, which can be cut short by pressing a key, then a line is executed.

The assembly language program produces machine code starting at address D01 hex. It also setsup function key 9 to enable OSWRCH to be vectored to the machine code and also switch on the Trace facility.

To use Acetrace, enter and run the listing. Then enter New and load in the Basic program to be debugged. Press function key 9 then run the Basic program. When you have seen enough, press Break followed by OLD. This restores the normal OSWRCH vector. Acetrace is still available by pressing function key 9 provided this has not been altered.

Dynvars produces a machine code routine starting at D01 hex. This code, when called, prints the names of all dynamic variables used by a Basic program.

To use it, enter the listing and run it. Then enter and run the Basic program. Entering

CALL &D01

will list the Basic program's variables.