Automatic Clock Configuration for PCI Express
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Solution Overview
Problem
In PCI Express systems, the distribution of a stable clock signal is challenging due to electromagnetic interference and clock skew, especially in large circuit boards or across backplane connectors, leading to potential bus performance deterioration.
Innovation Solution
An automatic clock configuration system that uses GPIO pins to determine whether a host device supports SRIS or SSC modes, allowing peripheral devices to select either a local clock or a common host clock, and further configures the clock buffer using bypass or PLL modes based on the host's capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common reference clock is distributed to all PCI Express devices, then clock synchronization is achieved, but clock skew and jitter increase due to electromagnetic interference over long routing paths
Solution Approach 1:
The patent divides the clock distribution system into separate segments: each device has its own local clock generator instead of relying on a single distributed reference clock. This segmentation eliminates the harmful effects of long routing paths while maintaining synchronization through coordinated operation of individual clock sources.
Solution Approach 2:
The patent introduces an intermediary mechanism (the capability indication signal exchanged between host and peripheral devices) that enables automatic selection between common reference clock mode and separate local clock mode. This intermediary allows the system to adaptively choose the optimal clock distribution approach based on device capabilities, resolving the contradiction between synchronization and signal quality.
2Adaptability or versatility
If a stable reference clock is routed over long distances across backplane connectors, then device connectivity is enabled, but electromagnetic interference and clock skew deteriorate bus performance
Solution Approach 1:
The patent implements dynamic clock configuration where the clock distribution mode (common reference vs. separate local clocks) is automatically selected based on device capabilities and routing conditions. This dynamic adaptation allows the system to maintain bus performance by switching to local clock sources when long routing paths are detected, while preserving connectivity options.
Solution Approach 2:
The patent changes the clock distribution parameter from fixed common reference clock to variable mode selection between common reference and separate local clocks. This parameter change enables the system to optimize clock signal quality by selecting appropriate distribution modes, thereby maintaining bus performance across different connectivity scenarios.
3Object-affected harmful factors
If separate local clocks are used at each PCI Express device, then clock skew is minimized, but compatibility with devices requiring common reference clock is reduced
Solution Approach 1:
The patent makes the clock distribution system universal by implementing support for multiple clock distribution modes (common reference clock and separate local clocks) within the same architecture. Devices can indicate their capabilities and automatically adapt to the appropriate mode, ensuring compatibility across different device types while minimizing clock skew when using local clocks.
Solution Approach 2:
The patent employs feedback mechanisms where devices exchange capability indications about their clock distribution preferences. This feedback enables automatic configuration of the optimal clock mode, ensuring broad device compatibility while allowing the system to select the mode that minimizes clock skew for each specific connection.
Data Source
AI summary
A method for automatic clock configurations is performed by a system having a host and a peripheral device. The host indicates on a first general-purpose input/output (GPIO) of a peripheral interface connecting the host and the peripheral device, whether the host supports a first clock configuration. The peripheral device receives from the first GPIO whether the host supports the first clock configuration. The peripheral device selects, in response to the host supporting the first clock configuration, use of a local clock of the peripheral device. The peripheral device selects, in response to the host not supporting the first clock configuration, use of a common clock of the host.