PCIe Port Surprise Hot Plug Detection in Low Power State
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Solution Overview
Problem
In the PCIe ecosystem, surprise hot plug operations can lead to erroneous states due to desynchronization between in-band and out-of-band presence detect fields when a PCIe port is in a low power state, preventing seamless hot plugging without disabling the low power state or surprise hot plug functionality.
Innovation Solution
The solution involves selectively ignoring the out-of-band presence detect field and delaying the transition from a detect quiet state to a detect active state, allowing the host to synchronize with the in-band presence detect field and ensuring accurate detection of device presence or absence, thereby preventing erroneous states during surprise hot plug operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the PCIe port enters a low power state (L1) to save energy, then power consumption is reduced, but the in-band presence detect field becomes out of synchronism with the out-of-band presence detect field during surprise hot plug operations, causing erroneous states
Solution Approach 1:
The patent introduces a detect quiet state as an intermediary state between detect active and low power states. During this intermediate state, the host delays transitioning from detect quiet to detect active, allowing synchronization of presence detect fields. This intermediary mechanism resolves the contradiction by providing a buffer period where the system can reconcile the out-of-sync fields before fully resuming detection, thus maintaining reliability while enabling low power operation.
2Measurement precision
If the host continuously monitors presence detect fields in real time, then detection accuracy is maintained, but seamless surprise hot plug operations cannot be performed while in low power state due to field desynchronization
Solution Approach 1:
The patent implements dynamic state transitions with a detect quiet state that allows the system to adapt its monitoring behavior. Instead of continuous real-time monitoring that prevents low power states, the system dynamically adjusts by entering detect quiet state during surprise hot plug events. This dynamic approach maintains detection accuracy when needed while enabling seamless hot plug operations during low power states, resolving the contradiction between measurement precision and adaptability.
3Reliability
If the host disables the low power state to prevent erroneous states during surprise hot plug, then detection reliability is maintained, but power savings are lost
Solution Approach 1:
The patent applies preliminary action by having the host enter the detect quiet state in advance before transitioning back to detect active state during surprise hot plug events. This preliminary intermediate state allows the system to prepare for potential field desynchronization issues by controlling the transition timing. The host can then selectively delay the detect quiet to detect active transition, ensuring fields are synchronized before resuming full detection, thus maintaining reliability while preserving power savings from low power states.
Data Source
AI summary
An apparatus is provided which comprises: an input/output (I/O) port; a first circuitry to update an in-band presence detect field, based on communication via an in-band channel; a second circuitry to update an out-of-band presence detect field, based on communication via an out-of-band channel; and a third circuitry to update a presence detect state change field, wherein the third circuitry is to selectively ignore the out-of-band presence detect field and utilize the in-band presence detect field, while the third circuitry is to update the presence detect state change field.