Thanks to lots of help from dwatson, the basics are working. dwatson suggested I modify certain config values for compiling the kernel.
Here are the steps required:
First, I built the kernel per the directions on http://wiki.chumby.com/mediawiki/index. … for_chumby
Then I opened .config with vi and added these lines:
Then, I remade the kernel with the following command line (and hit enter at every question thrown at me):
ARCH=arm BOARD=mx21ads CROSS_COMPILE=arm-linux- make all modules
That resulted in usbserial.ko and ftdi_sio.ko being added to the devices/usb/serial directory.
I put those files onto my usb memory stick, booted the chumby, ssh'd in, navigated to the stick's directory (/mnt/usb) and ran:
Then, I connected the arduino via USB2 and ran dmesg to verify that it is now attached at /dev/ttyUSB0.
If you need these files, you can get my copies at http://chumby.tokash.org/ftdi_sio.ko and http://chumby.tokash.org/usbserial.ko.
Excellent! More later! Thanks dwatson!!