DS90UH929-Q1 Datasheet, PDF (31/77 Pages) Texas Instruments – 720p HDMI to FPD-Link III Bridge Serializer with HDCP

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DS90UH929-Q1
SNLS458 – NOVEMBER 2014
8.5.2 Multi-Master Arbitration Support
The Bidirectional Control Channel in the FPD-Link III devices implements I2C compatible bus arbitration in the
proxy I2C master implementation. When sending a data bit, each I2C master senses the value on the SDA line.
If the master is sending a logic 1 but senses a logic 0, the master has lost arbitration. It will stop driving SDA,
retrying the transaction when the bus becomes idle. Thus, multiple I2C masters may be implemented in the
system.
If the system does require master-slave operation in both directions across the BCC, some method of
communication must be used to ensure only one direction of operation occurs at any time. The communication
method could include using available read/write registers in the deserializer to allow masters to communicate
with each other to pass control between the two masters. An example would be to use register 0x18 or 0x19 in
the deserializer as a mailbox register to pass control of the channel from one master to another.
8.5.3 I2C Restrictions on Multi-Master Operation
The I2C specification does not provide for arbitration between masters under certain conditions. The system
should make sure the following conditions cannot occur to prevent undefined conditions on the I2C bus:
• One master generates a repeated Start while another master is sending a data bit.
• One master generates a Stop while another master is sending a data bit.
• One master generates a repeated Start while another master sends a Stop.
Note that these restrictions mainly apply to accessing the same register offsets within a specific I2C slave.
8.5.4 Multi-Master Access to Device Registers for Newer FPD-Link III Devices
When using the latest generation of FPD-Link III devices, DS90UH929-Q1 or DS90UH940-Q1/DS90UH948-Q1
registers may be accessed simultaneously from both local and remote I2C masters. These devices have internal
logic to properly arbitrate between sources to allow proper read and write access without risk of corruption.
Access to remote I2C slaves would still be allowed in only one direction at a time .
8.5.5 Multi-Master Access to Device Registers for Older FPD-Link III Devices
When using older FPD-Link III devices, 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. This
would allow only the Host controller to access the serializer registers (local) and the deserializer registers
(remote). A controller at the deserializer 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 .
In a very limited case, remote and local access could be allowed to the deserializer registers at the same time.
Register access is guaranteed 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 one direction 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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