DS90UH940-Q1 Datasheet, PDF (46/87 Pages) Texas Instruments – FPD-Link III to CSI-2 Deserializer

DS90UH940-Q1
SNLS478A – NOVEMBER 2014 – REVISED JANUARY 2016
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8.5.5 Multi-Master Access to Device Registers for Older FPD-Link III Devices
When using older FPD-Link III devices (in backward compatible), simultaneous access to serializer or
deserializer registers from both local and remote I2C masters may cause incorrect operation, thus restrictions
should 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 an errored read or write.
Two basic options are recommended. The first is to allow device register access only from one controller. 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 second basic option is to allow local register access only with no access to remote serializer or deserializer
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.
8.5.6 Restrictions on Control Channel Direction for Multi-Master Operation
Only Display or Camera mode operation should be active at any time across the Bidirectional Control Channel. If
both directions are required, some method of transferring control between I2C masters should be implemented.
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