80-Bus News


January–February 1984 · Volume 3 · Issue 1

Page 13 of 55

Doctor Dark’s Diary – Episode 20.

Well, I never thought all those centuries ago that I would end up writing this many articles for the magazine! I think I owe you all thanks for putting up with me for so long, and to show you that you should not have done, here is my latest load of waffle.

I read the other day, somewhere or other, that the Nascom 1 is alive and well, and costs #50 in kit form from Lucas. You can’t keep a good machine down, and that’s a fact. You tell the kids of today you had to pay over #200 for one, and they’ll laugh in your face…

Another thing I chanced upon, in a weekly publication called “Computing”, was a review of Boris Allan’s book about Logo. At the bottom of the page was a picture of lots of school children in a room with lots of Nascom 3’s. It was nice to see that all the claims made by Acron about their monopoly are not 100% true after all. Apparently, Nasnet works. I have tried to use Acron’s Ekonet (the names have been changed so that I won’t be sued by the guilty!) but it is slower than first class post, when more than two people are using files on the same day!

And now, down to serious stuff, probably not a moment too soon! The Pluto graphics board is short of decent software, unless the people who are writing it don’t want it reviewed, and are advertising it in something I don’t read. Before you can get round to writing any really big programs for the thing, you need some sort of standard software interface to it. The one that follows is not quite complete, and one day I will get round to writing the definitive version. I have tried several times to write something like this, and have learned several interesting things from my failures along the way. My first versions were in assembler, and very effective, but I wanted something on a higher level, for ease of programming. The first attempt in Pascal was going to have a separate procedure or function for each of the functions of the Pluto board itself. As the set of routines grew longer, I kept compiling then, to check for errors. At a certain stage, the Hisoft Pascal 4 compiler became angry, and would not compile the end of the program. It works well enough with longer programs made up of fewer routines, so I can only assume that a stack somewhere is filling up, or maybe it is a table of addresses that gets too full? Anyway, it was a very ugly program, so I began again with a different approach.

What I really wanted to be able to do was write something along the lines of “pluto(plot,42,42)”, in which the name of the required routine and the necessary parameters were passed in the manner shown. But not all of the routines take the same number of parameters. And some return values, while others do not. Pascal does not provide a construction that will let you do anything so variable. So the version that follows is given only the routine name in the call, and a set of global variables that mimic the Pluto board’s internal variables must be set to the values you would have passed as parameters, had that been possible in Pascal. All clear? I thought not. If you want to set the current colour to red, you have to write:

ccol := red;

This is more or less friendly to use, but not by any means perfect! If anyone has any good ideas about how to improve matters, I for one would be glad to see them.

I know it is not as pretty as it should be, but it does work. At least, those parts that don’t say “not yet written” work! Any comments will be read with interest, and offers of Pluto Palette boards to test the next version with will be met with considerable grovelling.

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