Trammell Hudson of hackerspace NYC Resistor previously used the BeagleBone Black's PRU to drive LED video displays:
BeagleBone cape for OctoScroller LED matrix
His latest project drives the video display in the old Mac SE using the BeagleBone Black:
Mac-SE video - Trammell Hudson's Projects
Using the PRU in a BeagleBone Black to generate the sync and data signals to drive a Mac SE display. More info: trmm.net/Mac-SE_video
The resolution is 512x342 at 1 bit == 196 Kb, or 24 KB. Bit clock is 16 MHz, about 64ns per bit. Easily doable with BeagleBone Black PRU, but not from userspace due to the realtime constraints of generating the video signal. The source is github.com/osresearch/classicmac, but it is not ready for others to build yet.
Cheers,
Drew