8.7. LINK MAINTENANCE PROTOCOL
To initialize, explore, and recover from errors it is necessary to have a secondary mechanism to communicate between connected system devices. This mechanism is used to establish communications between connected devices, to attempt automatic error recovery and to allow software-managed link maintenance operations.
This protocol involves a request and response pair between electrically connected (linked) devices in the system. For software management, the request is generated through ports in the configuration space of the sending device. An external processing element write of a command to the link-request register with a maintenance write transaction causes a link-request control symbol to be issued onto the output port of the device, but only one link-request can be outstanding on a link at a time. The device that is linked to the sending device responds with a link-response control symbol if the link-request command required it to do so. The external processing element retrieves the link-response by polling the link-response register with I/O logical maintenance read transactions. A device with multiple RapidIO interfaces has a link-request and a link-response register pair for each corresponding RapidIO interface.
The automatic recovery mechanism relies on the hardware generating link-request control symbols under the transmission error conditions and using the corresponding link-response information to attempt recovery. Automatic link initialization ...
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