Slo-Trace

SLO-TRACE


by Antony Purvis


from Your Sinclair, January 1990





As well as fashionably omitting the 'w' of its name, Slo-Trace


distinguishes itself by being completely ace. You've probably all seen


a Trace program before. Anyone? No. Right. What they do is continuously


display the number of the line and statement currently being executed


while your (or anybody else's) Basic program is running. This is


remarkably handy for debugging, and can be put to 101 other uses.


(They elude me just now.)





Mind boggling, isn't it? But that's not all. Purv has once again


shattered the limits of Spectrum programming, dismissed with a


flourish of his hand the old machine's repressive impotence and come


up with yet another startling innovation. You can now slow down your


program while it's running to any speed you like to allow you to study


its intricacies in more detail. And then, of course, you can speed it


up again.





This incredible processing power comes at very little cost to your


fingertips. A mere 400 or so bytes of hex, a little Basic and you're


there. Well, the other way round actually. Bash in the Basic, save it


and then hammer in the hex using the hex loader. There are two bits of


hex, one to handle the interrupts (which are what make it work) and


the other bit is the routine itself. They'll need to be typed in and


saved separately.





Done that? Oh. Well, I'll carry on anyway. Contained in the Basic


program is all the info you'll need to get it going. The Trace routine


kicks in automatically, and the slowing down bit is controlled by


holding down Space and pressing '1' or '2' to alter the speed. The


border informatively indicates the rate things are running at. You get


it all on a plate, don't you?