Asymmetric Die-to-Die Interface Calibration via Hierarchical FSMs
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Solution Overview
Problem
Existing die-to-die (D2D) interfaces with asymmetric bandwidth cannot be calibrated using traditional methods, complicating the handshake process between dies due to unpaired transmit and receive endpoints.
Innovation Solution
A hierarchical organization of finite-state machines (FSMs) at macro, cluster, and node levels, with a calibration finite-state machine (CAL FSM) initiating and communicating calibration-related information through a back-channel to ensure synchronized calibration of asymmetric D2D interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional calibration methods are used for D2D interfaces, then symmetrical bandwidth calibration is achieved, but asymmetric bandwidth interfaces cannot be calibrated
Solution Approach 1:
The calibration process is segmented into multiple stages (first stage with CAL FSMs at macro level, second stage with cluster-level and node-level FSMs). This segmentation allows different calibration approaches for different interface types, enabling both symmetrical and asymmetric bandwidth calibration while maintaining reliability.
Solution Approach 2:
The calibration system dynamically adapts its behavior based on interface symmetry requirements. For asymmetric interfaces, the system uses unpaired transmit and receive endpoints with different calibration procedures, while for symmetrical interfaces, traditional paired endpoint calibration is used. This dynamic adaptation resolves the contradiction between bandwidth symmetry and calibration capability.
2Productivity
If asymmetric bandwidth is implemented in D2D interfaces, then optimized bandwidth assignment for specific use cases is achieved, but transmit endpoints cannot be paired with receive endpoints on the same die
Solution Approach 1:
The patent introduces intermediary FSM structures (cluster-level FSMs and node-level FSMs) that mediate between individual macro-level CAL FSMs and the overall calibration process. These intermediaries manage the complexity of unpaired endpoints by coordinating calibration across multiple macros, enabling asymmetric bandwidth implementation without overwhelming device complexity.
Solution Approach 2:
The patent adds a hierarchical dimension to the calibration architecture, organizing CAL FSMs into multiple levels (macro, cluster, node). This dimensional organization allows asymmetric bandwidth interfaces to be managed systematically through hierarchical coordination, transforming the complexity of unpaired endpoints into a manageable multi-level control structure.
3Adaptability or versatility
If unpaired transmit and receive endpoints are used in asymmetric D2D interfaces, then bandwidth asymmetry is supported, but the handshake process between D2D links is complicated
Solution Approach 1:
The handshake process is segmented into discrete calibration stages executed by hierarchical FSMs. Each CAL FSM manages handshake for its specific macro, while cluster-level and node-level FSMs coordinate across groups. This segmentation simplifies the overall handshake process for asymmetric interfaces by breaking it into manageable, independently controllable units with clear coordination protocols.
Data Source
AI summary
Systems and methods for initializing and calibrating asymmetric die-to-die (D2D) interfaces are described. As an example, during the calibration of a parameter, a calibration finite-state machine (CAL FSM) can perform certain measurements and adjustments. Once a stage of calibration is finished, the CAL FSM can communicate this information to a cluster FSM. The cluster FSM can then communicate to the node FSM the completion status. Once all the clusters have communicated to the node FSM that they have finished the current stage of calibration, the node FSM advances to the next stage of calibration and communicates to the pertinent cluster FSMs to advance, which in turn communicate to the CAL FSMs within the cluster to advance to the next stage of calibration. The clusters that are communicating in one direction are now able to receive the calibration stage information via other clusters that are communicating in the other direction.