Trace Stream Compression Switching for Adaptive Data Capture
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Solution Overview
Problem
The existing trace mechanisms, such as the Embedded Trace Macrocell (ETM), face limitations in bandwidth and efficiency due to fixed compression schemes that do not adapt well to varying patterns of trace elements, especially as processor complexity increases, leading to inefficiencies in trace data generation and storage.
Innovation Solution
The implementation of trace circuitry that can dynamically change compression schemes while still in operation, allowing for adaptation based on current patterns of trace elements, using a compression change stimulus to switch between overlapping bit pattern encoding spaces, thereby improving compression efficiency without halting the trace operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed compression scheme is used in trace circuitry, then the encoding space is non-overlapping and uniquely identifiable, but the compression efficiency cannot adapt to varying patterns of trace elements
Solution Approach 1:
The patent implements dynamic switching between multiple compression schemes by introducing a compression scheme identifier in the packet header. This allows the trace circuitry to adapt to varying patterns of trace elements while maintaining unique identifiability through the identifier field, resolving the contradiction between fixed encoding space and adaptive compression efficiency.
Solution Approach 2:
The patent changes the parameter of compression scheme selection by introducing a compression scheme identifier that can take different values. This allows the system to switch between multiple compression schemes (different parameter states) to optimize for different trace patterns, while the identifier ensures unambiguous interpretation at the receiver.
2Quantity of substance
If the trace buffer size is increased to store more trace elements, then the volume of trace data that can be generated increases, but the hardware requirements and bandwidth consumption increase
Solution Approach 1:
The patent applies compression schemes that change the parameter of data representation by encoding sequences of trace elements into compact packets. This reduces the volume of trace data that needs to be stored and transmitted, thereby reducing buffer size requirements and bandwidth consumption without losing trace information.
Solution Approach 2:
The patent segments sequences of trace elements into compressed packets with headers and optional payloads. This segmentation allows efficient storage and transmission by grouping related trace elements together, reducing the overall hardware requirements compared to storing individual trace elements separately.
3Measurement precision
If multiple compression schemes are supported with overlapping bit pattern encoding spaces, then compression efficiency improves through adaptation, but the trace analyzing tool must handle scheme changes
Solution Approach 1:
The patent introduces a compression scheme identifier as an intermediary element in the packet header. This identifier mediates between the multiple compression schemes with overlapping encoding spaces, providing the trace analyzing tool with explicit information about which scheme is currently in use, thereby simplifying the handling of scheme changes.
Solution Approach 2:
The patent performs preliminary action by including the compression scheme identifier in the packet header before the actual trace data. This allows the trace analyzing tool to know in advance which compression scheme is being used, enabling it to correctly interpret the subsequent data without having to detect or guess the scheme changes.
Data Source
AI summary
Trace circuitry, and a method of operating such trace circuitry, are provided for generating a trace stream indicative of activities of monitored circuitry of a data processing apparatus. The monitored circuitry produces data elements indicative of those activities, and the trace circuitry comprises trace element generation circuitry which is responsive to at least some of the data elements produced by the monitored circuitry to generate trace elements representative of those data-elements, with the trace elements generated being dependent on a selected trace mode of operation of the trace circuitry. Compression circuitry is then arranged to apply an encoding operation to a sequence of trace elements in order to produce a packet whose bit pattern represents the sequence of trace elements, and to cause that packet to be output in the trace stream, the encoding operation applied being dependent on a current compression scheme associated with the compression circuitry. Whilst in the selected trace mode of operation, the compression circuitry is responsive to a compression change stimulus to change the current compression scheme from a first compression scheme to a second compression scheme whose bit pattern encoding space overlaps the bit pattern encoding space of the first compression scheme, such that following the change of compression scheme any further packets produced whilst in the selected trace mode of operation are produced in accordance with the second compression scheme. Such an approach has been found to provide improved compression efficiency thereby reducing the volume of trace data produced.