80-Bus News

As a brief aside on FILL routines – You can always tell a recursive based FILL routine, as, when it is filling a complex area, there are often pauses while nothing apparently happens on the screen. What is actually happening is that the FILL routine has just filled to a ‘dead end’, and there then follows a period where the recursive structure ‘unwinds’ itself, returning from layer to layer back up the stack until it finds an area that it has not yet filled.

BUG TIME

Well folks, it had to happen. Between writing the first part of this article and completing this one someone has unearthed a bug that is present in both the IVC and SVC monitors. That fact that it has taken so long to surface is indicative that none of you are likely to have met it yet (otherwise you would have reported it – wouldn’t you?). It is in the ESC “f” ... sequence that allows you to redfine the function keys from a program. If you try and ‘undefine’ a key using this sequence the key is not actually fully deleted from the function key table, and if the key is subsequently pressed something will be returned to the host system. What the ‘something’ is cannot be easily predicted. Key definitions can be removed totally from the table, but only by using the Shift/​Edit feature direct from the keyboard.

TABLE 1: Extra features of the SVC