Got I2C interface working through the BBB-GVS Cape
It took a lot of work but we finally got the I2C1 interface working through the BBB-GVS cape. Turned out that the I2C port doesn't come enabled on a stock BBB Rev C card with Debian. Worked through it with the help of a few webpages. You can read how we did it here. If you have been trying to get I2C1 working you might find our page helpful.
We put together a video showing the I2C bus working.
Here's a picture of the setup we used.
We are feeling a bit sad since we are running out of things to test on the cape. We haven't communicated yet with the Configuration EEPROM but while we were working on the I2C bus we ran a bus probe and saw that the part was present as expected.