I2C arbiter chip application(PDF) from NXP.
The PCA9641 is highly integrated and smart design for 2-1 I2C-bus multiplexer. It is used in a system that needs two masters sharing the same slave devices. The internal switch is programmed by the masters but it will not switch in a middle of the task once owned by the master. The PCA9641 sends an interrupt to the master requesting the bus when the downstream bus is available. If the down-stream bus is hung, the initial/recovery function clears the downstream bus and sends status to both masters. Low voltage I2C masters can communicate with higher voltage level of slave devices.