Oh. If we're talking about going full-up DIY then there certainly are some other options. (I was sort of assuming we were looking for an off-the-shelf, or mostly so, solution.) I'd forgotten about the home-built "USB Video Card", that would certainly do the job.
But... Just thinking out loud/commenting on his design, he says he only managed to get about "four frames per second" raw data transit throughput from a 72Mhz ARM SoC over USB, which is only about 90kBytes a second, because the CPU is so contended between video updates and managing the external DRAM chip. I've seen a couple threads on the Parallax Propeller forums about using the Prop as an SPI slave where by using assembly they've claimed speeds on the order of 2.4Mbits/sec, which would of course divide down to something around 300kBytes/sec. That's still not super but it in theory pushes the uncompressed framerate up to close to 12-15 FPS. To go even faster you *might* be able to use something like a 74HC595 shift register to offload a little work at the cost of additional I/O pins on the Prop. A quick Google shows that Linux for the Pi has an SPI driver built in already that can clock up to *62 Mhz*. If with the aid of the shift register you could push the Prop up to around 5-6Mhz you could hit 30 FPS, which would be essentially realtime uncompressed.
Anyway, the Prop has 32k of RAM built in, more than enough for the 21k framebuffer, and it *should* be relatively trivial to modify the VGA driver to output to a single bit B&W TTL display like the Mac's. (It should be able to handle that with a single core, leaving you lots of cores to spread the load of handling the serial interface and shoving bytes into the framebuffer over.) The Prop's available in a traditional hacker-friendly 40 pin DIP package, so... it's a thought, anyway. The idea would essentially be to set up the Prop to drive the Mac's monitor on one side and behave roughly like the controllers for those SPI-interfaced LCD modules that are a dime a dozen on the other. To drive it, well, there are Linux drivers for those SPI LCDs, you should be able to pirate the code for your device.
But, eh. Then you have to develop it all over again. It looks like using the Prop isn't much cheaper than the ARM. A naked 40 pin DIP Propeller is about $7, while it looks like
you can get that ARM CPU on a breakout board for around $12. You will have to add the RAM chip as well, of course. The Propeller needs a $1.50 EEPROM for code storage, plus the shift register if you wanted to try that. Whee.
