Cliff Hacks Things.

Thursday, December 27, 2007

PropellerForth stirrings

A few weeks ago, I was poking around on the Silicon Valley Forth Interest Group webpage. I was surprised to see this in their minutes:
There has been no success in contacting the author of Propeller Forth - written locally by Cliff L. Biffle


As of about February 2007, my email got so clogged with spam that I simply stopped checking it. (Apologies to anyone who's been trying to contact me.) So, I had no idea that the SVFIG was interested in PropellerForth. I've had isolated inquiries from a couple people, but all in all, my original posts (here and on the Parallax forums) were met with general disinterest.

So, I've resurrected the project. Not much progress yet -- mostly, I'm cleaning up the sources so I can release them without sullying my good name. :-) People poking around the PropellerForth site on code.google.com might notice some documentation appearing in preparation for the source release.

Ever since I moved out of my folks' house, I've gone back and spent a few nights there for Christmas. Since my sleep schedule is rather different from theirs, I wind up having a lot of free time -- and since I'm away from work and distraction, it's traditionally been a great opportunity to hack. (Projects that got their start or reached significant milestones over Christmas include Mongoose, Cesta, PropellerForth -- and, 15 years earlier, WebElite.)

This year I learned the NTSC spec, the US analog television standard. The existing NTSC drivers for the Propeller are cryptic and don't build with propasm, so I wrote a very simple one with more lines of comment than code. It generates a 40x16 B&W text display, uses the ROM font to save space (compressing it on the fly to 8x16 pixels), and requires 336 bytes of code space and 640 bytes of framebuffer. As an experiment, I've tied it into PropellerForth.



It probably won't be part of the base image I release -- it bloats the image beyond my 8KiB target -- but between it and my PS/2 driver from Christmas 2006, I've nearly got a standalone console working.

(NTSC, incidentally, is a pain compared to VGA -- but most of the complexity, as my dad pointed out, is a result of sending all the data amplitude-modulated on a single channel, instead of VGA's five. It's kind of impressive that they got this to work in the 30s.)

So, if anyone following my blog is interested in PropellerForth, let this at least indicate that your interest may not be in vain.

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