There are two problems with I2C on the Chumby Hacker Board. First, it won't run at 400kHz (high speed) without a new kernel. Second, you need to continually poll the device.
Using the ATtiny4313 with only 256 bytes of ram, it would lose data even with a 200 byte buffer (for hex, so it would be about 80 bytes of messages). Nice -n -20 didn't resolve the problem, nor anything else I tried, so time to go serial.
I have several Nokia CA-42 cables. You can find them for around $5 from the cheap cell accessory places. Basically they are CR210x serial adapters, but are 3.3v friendly. Even better, if you rip off the plastic sheath, all the RS232 lines are there and a 5v passthrough. So I went back to my serial 115200 j1850 code, removed the molded jacket on one of these, and attached it. I modified the devgpsrc data sourcer code, and can't find a missed message. RPM was at 15.00 messages per second, the fuel messages were all in the low 20s (this is an incrementing counter, I will see a jump of 40 or 60 if a message is missed). All with 20Hz gps on the other channel.
It did stop in the middle of the ride, but the connector might not have been seated properly. Reseating it made it work for the rest of the ride.
I will try to post some pics later.
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