Debug Host Trace Synchronization for Processor State Reconstruction
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Solution Overview
Problem
Modern high-performance CPUs often lack data trace capability due to the high volume of data involved, which is difficult to extract and transfer efficiently, leading to limitations in reconstructing the state of processor cores and memory during debugging, especially with existing interfaces that consume too much power or are hard to route on a PCB.
Innovation Solution
A method in a debug host that synchronizes instruction and data traces to generate a synchronized trace, using a memory model that represents the memory accessible by processor cores, updating its state based on trace data and instructions, allowing for the reconstruction of any memory and processor state without the need for full data transfer, thereby reducing bandwidth requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full data tracing is implemented to reconstruct processor state, then debugging observability is improved, but bandwidth requirements and power consumption increase significantly
Solution Approach 1:
The patent extracts only the essential data needed for state reconstruction - specifically instruction traces and selective data traces - rather than capturing all processor data. This extraction approach removes unnecessary data volume while preserving the core debugging functionality, directly resolving the contradiction between observability and data volume.
Solution Approach 2:
The patent segments the tracing system into two distinct trace streams: instruction traces and data traces. This segmentation allows selective capture of only relevant data, reducing overall bandwidth requirements while maintaining the ability to reconstruct processor state when needed, thus resolving the contradiction between complete observability and data volume.
2Reliability
If data trace is captured for all memory accesses, then complete state reconstruction is enabled, but interface complexity and routing difficulty increase
Solution Approach 1:
The patent applies partial action by capturing data traces only for specific memory accesses that are necessary for state reconstruction, rather than all memory accesses. This selective approach maintains reliability for critical state information while reducing interface complexity and routing requirements.
Solution Approach 2:
The patent introduces a trace buffer as an intermediary component that stores trace data locally before transfer to the debug host. This buffer mediates between the complex trace generation process and the simpler debug interface, reducing the immediate bandwidth and complexity requirements of the external interface while maintaining complete state reconstruction capability.
3Adaptability or versatility
If instruction trace and data trace are separately extracted and synchronized, then trace processing flexibility is improved, but synchronization uncertainty increases
Solution Approach 1:
The patent employs feedback mechanisms where the debug host receives both instruction and data traces, correlates them based on timing relationships, and uses this correlated information to accurately reconstruct processor state. The feedback loop allows the system to adjust and refine synchronization based on the actual trace data, maintaining both flexibility and synchronization accuracy.
Data Source
AI summary
A method, performed in a debug host, for observing software execution on a computer having one or more processor cores, a cache attached to the one or more processor cores via respective execution pipelines forming a cache arrangement, and a memory, comprises obtaining an instruction trace of the cache arrangement and a data trace for data being loaded from the memory into the cache. The instruction trace is synchronized with the data trace to generate a synchronized data trace and/or a synchronized instruction trace. A state of a memory model, representing a memory readable by the one or more processor cores via a respective instruction is updated using the synchronized data trace and the synchronized instruction trace.