Yes, the prototype chumby was built around the MX21 - we used some of the Freescale drivers unmodified, modified some of them, and added others.

We are not currently using the accelerator because we were not sure we were going to be using the MX21 in the production model and didn't want to set incorrect expectations.

You can download our kernel and drivers from http://files.chumby.com/resources/chumby_kernel.tgz

We are not currently using the Hantro stuff.

However, my understanding is that the driver only does the very low-level packet decode and encode - there are  libraries that come with it that you link into your application take care of the timing, stream management, etc. which call in to the driver to decode or encode the individual packets.

I probably don't have any more documentation than you do.

I think the Hantro libraries include a small demo application that will decode and play a simple raw video file to the display.  It's up to you to integrate the libraries into your particular application - which would also have to handle any audio that might be in the file, controls, etc.

As far as I know, they don't provide a full featured application for playback of video - just crude demos.  I think you'd also have to handle management of any container formats as well - the demo apps are very simple and just scan for what it hopes are video packet headers.

This is from memory - it's been a while since I looked at that stuff.