Overview

If you’re unfamiliar with the Chumby, you should go to their website and check them out. They’re a ‘cute’ little Internet device that is meant to be an always-on appliance to “keep you connected” to your digital life. I have one on my night stand that is no more than a glorified alarm clock that I’ve had it since April of 2008 and justified the cost by saying it would be a new hobby since I love working with embedded systems devices. The enjoyment is even better since the Chumby is completely* “open” and there’s a very helpful community. Unfortunately life got in the way of the new potential “hobby” and it took until “paternity leave” for my second child for me to have any amount of free time to dedicate to hacking my Chumby. When the Chumby One was announced, I promptly ordered one since certain aspects were even easier for hacking (microSD rootfs, r/w filesystem, easier to “hack” case for adding a serial console).

The Idea

This project started because I wanted to be able to remotely start/stop Pandora radio as well as disable alarms if I woke up prior and didn’t want to wake up my wife. Chumby provides event interfaces for starting/stopping certain music sources, but Pandora isn’t one of them. ChumbyLurker has also written a nifty perl cgi script that will allow remote editing of alarms (which had a couple bugs) that wasn’t around when I came up with my idea. I have enough web experience as well as linux experience to get this working rather quickly, so off I went.

Getting to work

Step 1 – See how the touchscreen device is getting information to the Chumby flash player. With a quick look to the loaded modules, it was obvious the module “chumby_tsc2100″ was the touchscreen driver.

Step 2 – Obtaining the source was as easy as going to http://files.chumby.com/ which has the complete source for (almost) everything on the Chumby platform as it is (almost) all GPLv2 software. I imported all of the Chumby kernels available into a git repository for easy tracking of differences between firmware revisions as released by Chumby Industries.

Step 3 – Modify the source. I chose /proc entries as my “entry point” for emulating touches because I’m familiar with them so it would be a quick and easy way to get things working. With only a few lines of code in an hour or so, I was able to get emulated touch screen presses working by echoing coordinates to the new proc entry. Similarly I added an entry for the “bend” sensor on the top of the chumby.

$ echo "300 300" > /proc/chumby/touchscreen/coordinates
$ dmesg | tail -n 1
[2001256.670000] pen down - set coordinates x=1, y=1
$ echo "0 0" > /proc/chumby/touchscreen/coordinates
$ dmesg | tail -n 1
[2001261.680000] pen up
$ echo 1 > /proc/sense1
$ dmesg | tail -n 1
[2001395.680000] bent
$ echo 0 > /proc/sense1
$ dmesg | tail -n 1
[2001401.220000] not bent

If you’re a git user, you should be able to branch from 2.6.16, throw on the chumby kernel, then use git am to apply these patches:

• 0001-Turn-down-noise-in-sense-read
• 0002-Implement-a-forced-bend-sensor-press-proc-entry
• 0003-Implement-forced-touch-screen-pen-event-proc-entry

*Note: The control panel is not open source, although through the Chumby forums Chumby Industries respond to a lot of input from the community.