CPU Debug Mode Entry via Bus Interface State Switching
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Solution Overview
Problem
Conventional methods for forcing a central processing unit (CPU) to enter debug mode while busy with memory operations are complex and increase CPU complexity, potentially causing unexpected issues and making debugging difficult.
Innovation Solution
A CPU design incorporating a state memory and a bus interface unit that selectively couples the CPU core to bus contacts or a data generation unit based on the state, allowing for smooth entry into debug mode by generating dummy data when the CPU is waiting for memory responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a register switch is turned on to force the CPU core to abandon the unfinished instruction, then the CPU can respond to the debug mode request, but the CPU complexity increases and unexpected problems may occur
Solution Approach 1:
The patent introduces a debug mode entry circuit as an intermediary component that mediates between the debug request signal and the CPU core. This circuit generates a debug mode entry signal that controls the switching between normal operation and debug mode, avoiding the need to modify the CPU core's internal circuits. The intermediary circuit handles the complexity externally, keeping the CPU core simple while still enabling debug mode entry.
Solution Approach 2:
The patent segments the CPU system into distinct functional modules: the CPU core, the bus interface unit, and the debug mode entry circuit. By separating the debug mode control functionality from the CPU core, the system can enter debug mode without increasing the CPU core's complexity. Each module operates independently, with the debug mode entry circuit handling the mode transition while the CPU core continues its normal operations.
2Adaptability or versatility
If comprehensive control circuits are added to force abandonment of unfinished instructions, then the CPU can enter debug mode during memory operations, but the cost and complexity increase
Solution Approach 1:
The debug mode entry circuit serves as an intermediary that enables debug mode entry during any CPU operation without requiring comprehensive control circuits within the CPU core. This external circuit monitors the CPU's operational state and generates appropriate debug mode entry signals, providing adaptability across different operation types while maintaining CPU core simplicity.
Solution Approach 2:
The debug mode entry circuit provides a universal mechanism for entering debug mode regardless of the CPU's current operation state. Rather than implementing separate control circuits for different operational scenarios (memory read, memory write, instruction execution), a single multi-functional debug mode entry circuit handles all cases, reducing overall system complexity while maintaining versatility.
3Ease of operation
If the CPU core is forced to abandon unfinished instructions, then the CPU can respond to debugging requests, but the reasonability of internal operation may be compromised
Solution Approach 1:
The debug mode entry circuit acts as an intermediary that manages the transition to debug mode in a controlled manner. Rather than forcing the CPU core to abruptly abandon instructions, this circuit generates a debug mode entry signal that allows the CPU to transition to debug mode while preserving the state of unfinished instructions. This maintains operational reasonability by preventing data loss while enabling debuggability.
Solution Approach 2:
The system performs preliminary actions to preserve the state of unfinished instructions before entering debug mode. The bus interface unit and state memory capture the current operational state, ensuring that when debug mode is entered, the incomplete operations can be recovered and analyzed. This preliminary state preservation maintains operational reasonability while enabling subsequent debugging.
Data Source
AI summary
A central processing unit includes a core, a state memory, a plurality of bus contacts, a data generation unit, and a bus interface unit. The state memory stores a state, the bus interface unit is coupled to the core and the state memory, and the bus interface unit selectively couples the core to the plurality of bus contacts or the data generation unit according to the state.