SNLS477B October 2014 – November 2018 DS90UB948-Q1
When using older FPD-Link III devices (in backward compatible mode), simultaneous access to serializer or deserializer registers from both local and remote I2C masters may cause incorrect operation. Thus, restrictions must be imposed on accessing of serializer and deserializer registers. The likelihood of an error occurrence is relatively small, but it is possible for collision on reads and writes to occur, resulting in a read or write error.
TI recommends two basic options:
In a display mode system, this would allow only the host controller to access the serializer registers (local) and the deserializer registers (remote). A controller at the deserializer (local to the display) would not be allowed to access the deserializer or serializer registers.
The host controller would be allowed to access the serializer registers while a controller at the deserializer could access those register only. Access to remote I2C slaves would still be allowed in one direction (camera or display mode).
In a very limited case, remote and local access could be allowed to the deserializer registers at the same time. Register access is ensured to work correctly if both local and remote masters are accessing the same deserializer register. This allows a simple method of passing control of the bidirectional control channel from one master to another.