Microprocessor Pipeline Control for Future Instruction Scheduling
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Solution Overview
Problem
Conventional microprocessors face performance bottlenecks due to instruction stalling in the decode stage and increased complexity in managing operand and resource conflicts, which require continuous checking of resource availability and additional resources like queues to track pipeline conflicts.
Innovation Solution
The microprocessor tracks the availability of resources in the future and schedules instructions to be dispatched to the execution queue at that time, using a throughput counter to manage resource availability and a register file read/write control mechanism to optimize operand conflicts, thereby avoiding stalling and resolving conflicts in the decode stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If instructions are stalled in decode stage to resolve operand conflicts, then resource conflicts are resolved, but instruction execution performance deteriorates due to blocking subsequent instructions
Solution Approach 1:
The patent applies preliminary action by checking for operand availability and scheduling instructions in advance. The decode stage predicts future resource availability and schedules instructions accordingly, so that when resources become available, instructions are already ready to execute without stalling. This is achieved through the instruction queue that stores scheduled instructions and the counter that tracks future resource availability, allowing the system to prepare for resource availability before it occurs.
2Reliability
If instructions are put in execution queue to resolve conflicts, then resource conflicts are resolved, but system complexity increases due to multiple checking locations
Solution Approach 1:
The patent merges the conflict resolution function into the decode stage itself, combining resource availability checking with instruction decoding. Instead of having separate checking mechanisms in multiple locations (decode stage, execution queue, functional unit), the decode stage integrates all conflict detection and scheduling logic. The instruction queue simply stores scheduled instructions without active conflict checking, and the counter tracks resource availability centrally, eliminating the need for distributed conflict management.
3Reliability
If continuous resource checking is performed to track pipeline conflicts, then resource availability is monitored, but performance deteriorates due to blocking subsequent instructions
Solution Approach 1:
The counter tracks resource availability in advance for future time points, so that when an instruction needs to be decoded, the system already knows when the required resources will be available. This eliminates the need for continuous active checking during instruction execution, as the resource availability timeline is pre-computed and stored in the counter. Instructions are scheduled based on this pre-known availability information, allowing uninterrupted decoding while resources are busy.
Data Source
AI summary
In the disclosure, the microprocessor resolves the conflicts in decode stage and schedules the instruction to be executed at a future time. The instruction is issued to an execution queue until the scheduled time in the future when it is dispatched to a functional unit for execution. The disclosure uses a counter for the functional unit to track when the resource is available in the future to accept the next instruction. The disclosure also tracks the future N cycles when the register file read and write ports are scheduled to read and write operand data.