CPU Register Context Swap Mechanism for Zero Latency Interrupt Handling
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Solution Overview
Problem
Current CPUs face significant latency due to interrupt context switching, which can be up to 28 CPU cycles long, limiting performance in applications with frequent high-priority interrupts and short interrupt service routines.
Innovation Solution
A central processing unit (CPU) with a plurality of context-defining register sets and an interrupt unit that automatically or manually switches between these sets based on interrupt priority levels, using a context status register to control and initiate context switches with zero overhead, allowing transparent context swapping during exceptions and interrupt processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional interrupt context switching is used, then interrupt handling is supported, but context switching latency is introduced (up to 28 CPU cycles)
Solution Approach 1:
The patent divides the single register set into multiple context-specific register sets (e.g., CONTEXT0, CONTEXT1, CONTEXT2, CONTEXT3), each capable of storing a complete CPU context. This segmentation allows the CPU to switch between pre-defined contexts without performing full save/restore operations, thereby eliminating context switching latency while maintaining interrupt handling capability.
Solution Approach 2:
The patent pre-configures multiple register sets with specific context information before interrupts occur. Each register set is assigned to specific interrupt priority levels through fuse configurations, so that when an interrupt occurs, the CPU can immediately switch to the pre-prepared register set without any latency. This preliminary preparation of contexts resolves the time loss issue.
2Loss of time
If multiple register sets are introduced for context switching, then context switching latency is eliminated, but device complexity increases
Solution Approach 1:
The patent implements automatic context switching through hardware mechanisms. The interrupt unit automatically selects and switches to the appropriate register set based on the interrupt priority level, without requiring software intervention or complex control logic. This self-service approach eliminates the need for complex context management software while reducing context switching latency.
Solution Approach 2:
The multiple register sets serve dual purposes: they function as both the standard CPU registers during normal operation and as pre-configured context storage for interrupt handling. This multi-functionality reduces the need for separate context storage mechanisms, thereby limiting the increase in device complexity while achieving zero-latency context switching.
3Productivity
If automatic context switching is implemented, then interrupt handling efficiency is improved, but power consumption may increase
Solution Approach 1:
The patent implements partial context switching by maintaining multiple register sets that are only fully utilized when needed. The CPU can operate using a single active context for extended periods, switching to pre-configured register sets only when interrupts occur. This partial utilization approach improves interrupt handling efficiency while minimizing the additional power consumption associated with maintaining multiple active register sets.
Data Source
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AI summary
A central processing unit (CPU) having an interrupt unit for interrupting execution of instructions, a plurality context defining register sets, wherein each set of registers having the same number of CPU registers, a switching unit for coupling a selected register set within the CPU, wherein the switching unit switches to a predetermined register set of the plurality of context defining register sets upon occurrence of an exception, and a control register configured to control selection of a register set of the plurality of context defining register initiated by an instruction and further operable to indicate a currently used context.