Unified Exception and Error Recovery in Processing Pipelines
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Solution Overview
Problem
Existing data processing systems face challenges in efficiently handling errors and exceptions without increasing area and power consumption, particularly when dealing with speculative execution and register renaming, as they require additional stages and storage for error detection and recovery.
Innovation Solution
A data processing apparatus with a processing pipeline that includes exception control circuitry for error detection and storage, allowing for the maintenance of an age-ordered list of instructions with error and exception indicators, enabling recovery from errors and exceptions using existing exception handling circuitry, and register renaming circuitry that updates renaming tables with error information for speculative instructions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error detection and recovery means are added to detect and correct timing errors, then system reliability is improved, but device complexity and area increase
Solution Approach 1:
The patent merges error detection and exception handling into a unified mechanism. The exception detection circuitry is extended to also detect timing errors by monitoring the same output signals, and both error types are handled through the same exception table and recovery procedures. This consolidation eliminates the need for separate error detection and recovery circuits, thereby improving reliability without significantly increasing device complexity.
Solution Approach 2:
The exception handling infrastructure is given multi-functionality to serve both exception instructions and timing error recovery. The exception table stores information for both types of events, the detection circuitry monitors for both conditions, and the recovery mechanisms handle both cases. This universal approach allows the system to gain enhanced reliability while reusing existing structural components.
2Reliability
If pipeline is increased by two clocked stages to detect error signals, then error detection capability is improved, but area and power consumption increase
Solution Approach 1:
The patent combines error signal detection with the existing exception detection infrastructure. Instead of adding separate detection stages, the system uses the same circuitry that detects exceptions to also detect timing errors. The error signal is integrated into the existing exception handling flow, allowing error detection without extending the pipeline by additional clocked stages, thereby avoiding the associated area and power penalties.
3Reliability
If safety margins are added to clock frequency and operational voltage, then system reliability is improved, but productivity decreases
Solution Approach 1:
The patent implements preliminary error detection by monitoring output signals during the speculation region at the end of the clock cycle. By detecting potential timing errors before they propagate through the pipeline, the system can correct errors without needing to reduce clock frequency or voltage to safe levels. This allows the processor to operate at higher performance points while maintaining reliability through proactive error detection and correction.
Solution Approach 2:
The system uses feedback from the speculation region to detect timing errors and trigger corrective actions. The error detection circuitry monitors output signals and feeds back error information to the exception handling mechanism, which then corrects the error by retrieving the correct value from the exception table. This feedback loop enables the system to operate without conservative safety margins while maintaining high reliability.
4Productivity
If register renaming is used to process instructions out of order, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent combines exception handling information with register renaming data in the exception table. Each entry in the exception table contains both the program counter value and the architectural register state associated with a particular instruction point. This integration allows the system to handle exceptions and timing errors in out-of-order execution environments without requiring separate complex tracking mechanisms, thereby improving productivity while managing device complexity through unified data structures.
Data Source
AI summary
A data processing apparatus with a processing pipeline, the pipeline including exception control circuitry and error detection circuitry. An exception storage unit is configured to maintain an age-ordered list of entries corresponding to instructions issued to the processing pipeline for execution. The unit is configured to store, in association with each entry, an exception indicator indicating whether the instruction is an exception instruction and whether it has generated an exception and an error indicator indicating whether the instruction has generated an error. The apparatus is configured to indicate to the exception storage unit that an instruction is resolved when processing of the instruction has reached a stage such that it is known whether the instruction will generate an error and whether the instruction will generate an exception; and the exception control circuitry is configured to sequentially retire oldest resolved entries from the list in the exception storage unit.