ACPI Sleep-State Control via CPU-Only Reset Register
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Solution Overview
Problem
Conventional methods for transitioning a computing device to firmware control during sleep-state changes require dedicated hardware support, such as System Management Mode (SMM), which not all ACPI-compliant devices possess, limiting their ability to manage sleep-states effectively.
Innovation Solution
The implementation of a CPU-only reset register and firmware code execution at a known CPU reset vector, allowing the operating system to trigger a CPU-only reset and execute firmware code before entering a sleep-state, even in devices lacking SMM support, by altering the Fixed ACPI Description Table (FADT) and Differentiated System Description Table (DSDT) to redirect the sleep-state transition sequence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods using SMM are used for sleep-state transitions, then firmware control during sleep-state changes is achieved, but device complexity increases and adaptability decreases for devices without SMM support
Solution Approach 1:
The patent introduces a CPU reset mechanism as an intermediary to achieve firmware control during sleep-state transitions. Instead of requiring SMM support, the system uses a CPU reset vector that redirects execution to firmware code when specific register values are written, enabling the same functionality on devices without SMM.
Solution Approach 2:
The patent changes the parameter used to trigger firmware execution from SMM-specific mechanisms to CPU reset register values. By modifying the Fixed ACPI Description Table (FADT) to use CPU reset registers instead of SMM triggers, the system achieves firmware control through parameter changes that are compatible with standard CPU architectures.
2Reliability
If SMM support is required for sleep-state transitions, then secure firmware execution is achieved, but device complexity and hardware requirements increase
Solution Approach 1:
The patent extracts the essential function of firmware execution during sleep-state transitions from the SMM subsystem. By separating the firmware execution requirement from the SMM hardware feature, the invention achieves secure firmware execution using only standard CPU reset mechanisms, removing the need for specialized SMM hardware support.
Solution Approach 2:
The patent replaces expensive specialized SMM hardware support with a simple CPU reset mechanism that is universally available on standard processors. This substitution uses readily available CPU reset vectors and registers instead of requiring dedicated SMM hardware, reducing device complexity while maintaining security.
3Reliability
If dedicated firmware function calls are used for sleep-state transitions, then control transition is achieved, but ease of operation decreases due to platform-specific requirements
Solution Approach 1:
The patent makes the sleep-state transition mechanism universal by using CPU reset registers that are standard across different processor architectures. The Fixed ACPI Description Table (FADT) is configured to use CPU reset vectors, allowing the same mechanism to work across different platforms without requiring platform-specific firmware function calls or SMM support.
Data Source
AI summary
A mechanism for firmware to gain control from the operating system of an Advanced Configuration and Power Interface (ACPI)-compliant computing device during sleep-state transitions even if the computing device lacks a dedicated means for such a change to occur is discussed. Embodiments of the present invention report a CPU-only reset register in place of a sleep control register for an ACPI-compliant computing device in which an operating system is attempting a sleep-state transition. A CPU reset value is substituted for a sleep type value in a sleep-state object and written to the CPU-only reset register that was reported instead of the sleep control register thereby triggering a CPU-only reset. Firmware code operating at a known CPU reset vector may perform specified processing and then authorize a transition to the originally requested sleep-state.