Arbiter Interleaves Debug Instructions in Processing Pipeline
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Solution Overview
Problem
Existing debug mechanisms for data processing systems face challenges in efficiently executing debug program instructions alongside non-debug instructions, particularly in maintaining memory coherence and handling asynchronous memory access, which can lead to confusion and incorrect aborts during debug operations.
Innovation Solution
The proposed solution involves a processing pipeline with an arbiter that arbitrates between debug and non-debug program instructions, using a debug interface to receive and translate debug command signals into instructions, and employing proxy circuitry to manage memory access synchronously, ensuring that debug instructions are executed without interfering with non-debug operations, even in sleep modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If debug program instructions are executed by halting program instruction execution and serially scanning into the target apparatus, then debug operations can be performed, but system productivity is reduced due to execution halts and serial processing
Solution Approach 1:
The patent merges debug program instructions with non-debug program instructions into a single instruction buffer, allowing both types of instructions to be stored together and executed interleaved through the processing pipeline. This eliminates the need to halt execution for debug operations, as debug instructions are processed alongside normal program instructions in sequence.
Solution Approach 2:
The instruction buffer is designed to serve dual purposes: storing both debug program instructions and non-debug program instructions. The processing pipeline is also made universal by capable of executing both debug and non-debug instructions through the same execution stages, eliminating dedicated separate paths for debug operations.
2Productivity
If debug instructions are intermixed with non-debug instructions in the instruction buffer, then productivity is improved by avoiding execution halts, but device complexity increases due to arbitration requirements
Solution Approach 1:
The arbiter is implemented as logic integrated within the existing instruction buffer structure, utilizing the buffer's own control signals and instruction metadata to automatically distinguish and prioritize debug instructions. The system self-manages the arbitration process using resources already present in the instruction buffer, minimizing additional complexity.
3Reliability
If debug instructions are executed through a separate debug access port using load and store instructions, then debug information can be gathered, but device complexity increases and productivity decreases due to separate access path
Solution Approach 1:
The patent merges the debug instruction execution path with the normal program execution path. Instead of using a separate debug access port with load and store instructions, debug instructions are executed through the same processing pipeline that handles non-debug instructions, utilizing shared execution resources including ALUs, registers, and memory interfaces.
Solution Approach 2:
The processing pipeline is designed with universal execution capability to handle both debug and non-debug instructions through the same stages. The same execution units, register files, and memory subsystems serve both debug and normal program operations, eliminating the need for dedicated separate circuitry.
4Productivity
If memory access is handled asynchronously during debug operations, then productivity is maintained, but reliability deteriorates due to memory coherence issues and incorrect aborts
Solution Approach 1:
The patent implements feedback mechanisms where the arbiter monitors memory access requests from both debug and non-debug instructions, tracks memory coherence state, and adjusts instruction issuance accordingly. This feedback loop ensures that debug instructions receive accurate memory data and that memory operations maintain coherence, preventing incorrect aborts while maintaining continuous operation.
Data Source
AI summary
A target apparatus 2 for debug includes a processing pipeline 18 for executing a sequence of program instructions. A debug interface 26 receives debug command signals corresponding directly or indirectly to debug program instructions to be executed. An instruction buffer 24 stores both the debug program instructions and non-debug program instructions. An arbiter 30 selects between both the debug program instructions and the non-debug program instructions stored within the instruction buffer to form the sequence of program instructions to be executed by the processing pipeline. A complex coherent memory system 4, 6, 8, 10, 12, 14, 32 is shared by the debug program instructions and the non-debug program instructions such that they obtain the same coherent view of memory.