I2C to SPI converter
This is a simple I2C to SPI bridge. It's implemented in an ATTiny85. The ATTiny85 acts as an I2C slave, and relays the data out a SPI port.
The implemenation is unidirection, e.g. supports only writes to I2C.
The implementation only expects the device address, and then two bytes of data. Once the two bytes of data are received, they are instantly shoved out of SPI. During the SPI phase the ATiny85 is unresponsive to I2C.
All ports are implemented using bitbang.
Requires the ATTiny85 to be fused to run in 8MHz RC osc mode.
Few I2C error cases are handled. The device will successfully ignore all commands to devices that aren't it's address, but once you address the device, you must send two bytes to it. If you're short or you're too long, the behavior isn't defined.
This code is targeted to AtmelStudio. It's not for Arduino.