Link Layer Encoding Transition via DLLP Handshake
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Solution Overview
Problem
Computer bus systems face challenges in seamlessly transitioning between different data rates and encoding mechanisms, such as flit-based and packet-based encoding, which can lead to disruptions in link layer sequencing and require taking the link down for reconfiguration.
Innovation Solution
Implementing a Data Link Layer Packet (DLLP) handshake mechanism to inform link partners of the last sequence number in the prior encoding when transitioning from flit-based to packet-based encoding, and preserving the existing PCIe link layer retry mechanism across different data rates without taking the link down.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the link transitions between different data rates and encoding mechanisms (flit-based to packet-based encoding), then the system can adapt to different performance requirements, but the link layer sequencing is disrupted and the link must be taken down for reconfiguration
Solution Approach 1:
The patent applies preliminary action by exchanging DLLP packets containing sequence number information before the actual data transmission resumes after a rate transition. The transmitting device sends a DLLP with the last sequence number of the prior encoding, and the receiving device responds with an acknowledgment DLLP, ensuring both devices are synchronized before resuming normal operation. This preliminary synchronization prevents sequencing disruptions without requiring link shutdown.
Solution Approach 2:
The patent uses DLLP (Data Link Layer Packet) as an intermediary mechanism to facilitate the transition between different encoding schemes. The DLLP carries sequence number information that acts as a mediator between the flit-based and packet-based encoding domains, allowing the link to maintain continuity while adapting to different data rates and encoding mechanisms.
2Adaptability or versatility
If the link is taken down for reconfiguration during rate changes, then encoding mechanisms can be properly switched, but communication downtime increases
Solution Approach 1:
The patent maintains continuity of useful action by keeping the link in an active state throughout the encoding mechanism transition. Instead of shutting down the link, the system continues to exchange DLLP packets that carry the necessary synchronization information, allowing the transition to occur without interrupting the overall communication flow and minimizing downtime.
3Reliability
If sequence numbers are not synchronized during encoding transitions, then link partners may lose track of data, but maintaining synchronization requires additional communication overhead
Solution Approach 1:
The patent applies universality by using the existing DLLP mechanism for multiple purposes: normal data link layer communication and sequence number synchronization during encoding transitions. The same DLLP structure carries both data and synchronization information, eliminating the need for separate complex synchronization protocols and reducing overall system complexity.
Data Source
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AI summary
In one embodiment, an apparatus includes: a transmitter to send a first plurality of flits to a second device coupled to the apparatus via a link; and a control circuit coupled to the transmitter to change a configuration of the link from a flit-based encoding to a packet-based encoding. In response to the configuration change, the transmitter is to send a first plurality of packets to the second device via the link. Other embodiments are described and claimed.