I'm actually using i2c RTC Clock, but wrote it in a hurry as SPI, my brain wasn't working
I'm moving away from usb which is causing me lots of issues with bluetooth. I got HC-05 module which has serial, spi and i2c communication options. Which would you use? Serial is probably most straight forward, but requires lots of modifications on Carambola 2 to make it work, and then I loose serial for debugging.
Link you send for SPI is just what I was looking for! Thanks.