What answers on the bus.
How many steps a script has left, or null when the bus is not scripted.
How many transfers have been made on the bus, by the program and every driver on it, including any that failed.
How long the drivers on the bus have asked to wait, in microseconds, whether or not the process slept through it.
Reads length bytes from a part in one transaction.
Writes bytes to a part in one transaction: usually a register address and its value.
Writes bytes and then reads length bytes in one transaction, with a repeated start
between them, which is how a register is read.
One I2C bus, shared by the program and every driver built on it.
Transfers run one at a time, synchronously; each is quick, the time a few bytes take on the wire. A failed transfer throws with the reason: nothing answered at the address, the script expected something else, or the kernel's own words.