Trying to track this down further - I don't have my Guruplugs in yet. These are my notes as I attempt to use the schematics and pictures available to figure out what's going on.
There appear to be two separate boards, one is the main board and the other is a daughter-battery/cards/wireless board. The two boards interface via a pair of Hirose-style pressfit surface mount connectors, J6 and J7 on the daughter board and J14 and J15 on the mainboard. J14=J6 and J15=J7.
On the daughterboard, the wireless chip (AzureWave AW-GH381, I think, can't find a datasheet yet) appears to have I2C pins going in or coming out of it which are available at TP8 and TP13. Also, J6 has pins 23 and 24, SCK_CTS0 and SDA_RTS0 which look promising. It looks like these pins dead end here, though, I don't see anything connected to them on the schematic and the pins are not routed out. Guess I can solder wires to the connector pins (yay, that's gonna look real professional).
On the mainboard, we seem to have U15, which is not stuffed. This looks like a serial EEPROM (there is a board option for a serial rom initialization disable function as well). The IO pins SCK_CTS0 and SDA_RTS0 (sounds familiar) are routed in the schematic to J14 and come from U1H (which is the Marvell chip).
Great. I would have SWORN
that the Guruplug pages advertised I2C functionality when I ordered this, but they do not now. Wonder if I kept printed copies of that. It is quite clear that the plug does not currently offer I2C as a real option, because they didn't bother to hook it up despite sufficient board real estate to insert a RS-232 connector.
If you need I2C like I do it looks like your choice is
- Solder directly to pins 23 and 24 of J6 and accept the unprofessional-looking result
- Remove the daughterboard, go without USB, wireless and cards, and plug your own board in
- Build a sandwich board to go in between (and good luck getting the connectors properly located)
Crap. Thanks a ton, Globalscale, really helping me out here.