potatohead's Blog - Propeller supplied graphics objects

RSS Bot · November 1, 2006

Been tinkering with the supplied graphics engine. It reminds me of the C64 in that color defintions are tile based.

Essentially, you get 4 color values per pixel. What colors those values actually generate depends on the color information defined for that particular 16 x 16 pixel tile. There is no real limit on the number of unique tile color set definitions however. Essentially, you get a full color screen, but only 4 of them per tile area.

Interesting...

The assembly language is cool and I'm starting to get it. Like this little chip a lot. There are no in-cpu registers, there is no indexing and it's 32 bit across the board. Does have barrel shifter. Nearly all instructions local to the CPU (there are 8 running together) take 4 cycles to complete.

"Registers" are really pointers to the 512 longs that compose the 2Kb local memory. So, a move between memory locations is really just move x,y. Compares, adds, all work the same way! To index, you self modify one of the instructions with another one and branch accordingly.

What's nice is the lack of having to deal with lots of addressing modes. Really operands are immediate and specified by direct address. That's it, aside from dealing with the program counter.

The higher level language maps almost directly to the assembly language and provides structure. It's really easy to mix the two for the best balance of speed and utility. Their own graphics kernel is assembly, wrapped in a higher object that gets called by other programs. frankly, the provided environment reminds me a lot of a higher level Batari Basic environment.

First real task is to code a readpixel function object into their graphics library. It's missing this, making simple games difficult! I'm working through their write pixel routine for this. If what I do works out, they will probably just include it with the next distribution. I'm liking the openness of it all so far.

A budding demo scene is beginning to show, egged on by the chips creator having worked out a very decent software speech engine on the thing.

Was really bummed about my total mistake about how the 7800 cart port works. Not sure what I plan to do with this chip and classic machines just yet. Still thinking.. Might not do anything in the end. For now, the plan is to just get myself up to speed on the programming and see where that leads.

With the talent here, some really great stuff could be built. In the end, I suppose that's why I'm posting this stuff here. --that and this is really the closest venue besides there own more EE and robotics based forums. After watching what has happened so far, a simple yet very functional console could be produced for the price of a really great homebrew cart. One has been designed that's quite advanced --it's gonna be about $250. For now I'm gonna ignore that in favor of the core processor and demo board I'm working on now.

http://www.atariage.com/forums/index.php?a...;showentry=2278