I got the parts in from digikey today, and assembled a couple of the rStep boards. Seems that sanguino uses the 644p and I ordered the 644. Additionally, I’m clocking the 644 at 20Mhz while the sanguino expects 16Mhz. I had to make a number of changes to make the 644 work with the arduino. First, I had to modify the bootloader by adding an entry for the 644 @ 20Mhz, recompiled it, and uploaded it through the JTAG port. Additionally, the boards.txt file had to be changed to reflect the 644 @ 20Mhz. Now, it is compatible with the arduino IDE and I was able to compile a simple LED blinking application and upload it without problems. A few more tests and I’ll be able to send out the beta boards to the developers for further testing.