Trace Circuitry for Conditional Instruction Diagnostics
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Solution Overview
Problem
In advanced processors with multiple execution stages and out-of-order instruction execution, tracing the pass/fail result of conditional instructions is challenging due to unpredictable availability of execution results, making it difficult to monitor processing operations effectively.
Innovation Solution
The approach involves tracing condition flag values instead of pass/fail results, which are typically more readily available and part of the architectural state, allowing for simplified tracing by generating trace data elements that include current or identified values of condition flags, reducing the complexity of trace circuitry and bandwidth constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pass/fail results of conditional instructions are traced directly, then diagnostic accuracy is improved, but trace circuitry complexity and bandwidth requirements increase due to unpredictable availability in out-of-order execution pipelines
Solution Approach 1:
The patent introduces condition flags as intermediary data that mediate between the complex out-of-order execution pipeline and the trace circuitry. Instead of directly tracing unpredictable pass/fail results from multiple execution stages, the trace unit monitors condition flags which are updated deterministically by condition code setting instructions. This intermediary approach simplifies the trace circuitry while maintaining diagnostic accuracy, as the condition flags provide a stable reference point for analyzing conditional instruction outcomes.
2Loss of information
If pass/fail results are monitored in real-time, then processing outcome determination is improved, but trace bandwidth consumption increases due to frequent updates from parallel execution stages
Solution Approach 1:
The patent extracts only the essential information needed for diagnostic purposes - the state of condition flags - rather than tracing all pass/fail results from every execution stage. By selecting and extracting only the relevant condition flag updates that occur at instruction commit points, the system determines processing outcomes while significantly reducing trace data volume. This selective extraction approach maintains diagnostic capability while minimizing bandwidth consumption.
3Device complexity
If condition flags are traced instead of pass/fail results, then trace circuitry complexity is reduced, but difficulty in determining when execution results are available increases
Solution Approach 1:
The patent employs a self-service mechanism where the trace unit automatically detects condition flag updates through dedicated trace ports that monitor the condition code register. The system uses control flags within the trace unit to automatically track which condition flags have been traced, eliminating the need for external coordination or complex timing logic. This self-service approach reduces circuitry complexity while solving the execution result availability problem through automated flag state monitoring.
Data Source
AI summary
A processing circuit is responsive to at least one conditional instruction to perform a conditional operation in dependence on a current value of a subset of at least one condition flag. A trace circuit is provided for generating trace data elements indicative of operations performed by the processing circuit. When the processing circuit 4 processes at least one selected instruction, then the trace circuit generates a trace data element including a traced condition value indicating at least the subset of condition flags required to determine the outcome of the conditional instruction. A corresponding diagnostic apparatus uses the traced condition value to determine a processing outcome of the at least one conditional instruction.