i2c interface design

See I2C interface API for details on the interface and how to use it.

i2c::transaction()

The singular transaction API can support all forms of standard i2c communication operations such as read, write, and write then read. It also comes with a timeout parameter which indicates to the i2c driver when a transaction should abort. Normally applications and drivers will use hal::never_timeout for parameter, unless an external device has the capability/need to perform clock stretching on the bus.

The APIs for transaction were not split up into a separate read(), write() and write_then_read() functions in order to reduce vtable size to just two entries. Many i2c implementations incorporate all of these operations in the same algorithm or interrupt state machine which matches the current API structure.

The separate operations can be made available using the i2c utility functions in libhal-util.

i2c::configure()

There is not much to say about configuration for i2c. There really is only one option that is variable with i2c an that is clock speed. Everything else is device and target specific.