> No way to safely bring the bus back to idle from mid-transaction.
Why would you want to do that? Not having the ability to do this is part of the contract. If you design your device such that it always completes the transaction, then there should be no problem, unless one of the devices on the bus doesn't play fair but then you have a different problem.
Say you’ve asked an I2C ROM for a block read. After the first byte something, also on the bus, asserts an interrupt via a side band GPIO. I can’t read the something until the block read finishes.
The specific case I was thinking of was the host suffering an incident where it is not possible or practical for its software to know where it left off.
For example, you get a kernel panic, or soft-reset for some reason. When you recover, you now have a bus in an unknown state, possibly mid-transaction, and if you pick the wrong order in which to bring the bus back to idle, you might wedge it or accidentally cause a side-effect (e.g overwrite a byte in an EEPROM).
But doing bus communication from software is generally a bad idea. Best is to use a hardware controller dedicated to the task. Do you have examples for bus protocols that can be run from software?
Why would you want to do that? Not having the ability to do this is part of the contract. If you design your device such that it always completes the transaction, then there should be no problem, unless one of the devices on the bus doesn't play fair but then you have a different problem.