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Five-Stage Pipeline Partitioning and Timing Contracts: Debug Playbook
Debug Playbook for Five-Stage Pipeline Partitioning and Timing Contracts.
Debug playbook
Debug Playbook for Five-Stage Pipeline Partitioning and Timing Contracts is anchored on Post-layout Fmax versus stage slack spread, plus bubble rate introduced by stage-boundary timing fixes.. Convert observations into mechanism-backed decisions with explicit ownership.
Freeze workload seed, binary, compiler, firmware, and platform setup.
Find earliest persistent mechanism failure in the timeline.
Build one reduced reproducer for dominant hypothesis.
Patch minimal fix with explicit rollback gate.
Rerun correctness + performance + power matrix.
Decision tree
diagram
ROOT CAUSE TREE - Five-Stage Pipeline Partitioning and Timing Contracts
Post-layout Fmax versus stage slack spread, plus bubble rate introduced by stage-boundary timing fixes. regressed
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reproducible on fixed seed?
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no yes
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env/tool drift first failing domain?
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decode execute memory/MMU
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control map bypass/FU TLB/walk/perm
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privilege/CSR side effects checked?
Stop at first confirmed mechanism, then assign explicit owner + fix proof.Review memo template
diagram
RISC-V REVIEW MEMO - Pipeline Implementation / Five-Stage Pipeline Partitioning and Timing Contracts
1. Symptom
- Failing metric: Post-layout Fmax versus stage slack spread, plus bubble rate introduced by stage-boundary timing fixes.
- Failing workload slice: <name>
- Triggering mode: <privilege/virtualization/interrupt/cache/boot>
- Build and runtime tags: <toolchain/firmware/RTL revision>
2. Mechanism hypothesis
- Primary mechanism: A classic in-order RISC-V core splits work into IF, ID, EX, MEM, and WB so each cycle advances one instruction per stage under no-hazard conditions. Real implementation quality depends on what logic is placed on each boundary: decode complexity, immediate generation, register-file read timing, branch compare placement, and load-use critical paths determine whether balanced stage delays are achievable. Pipeline registers carry both data and control intents (destination register, write enables, memory mode, exception metadata), and these intents must remain aligned through stalls and flushes. Reliable designs define explicit stage contracts for valid/kill semantics, side-effect timing, and exception priority, then prove those contracts with assertions and directed timing-stress tests before frequency signoff.
- Competing hypotheses: <decode control / hazard / MMU / privilege / integration>
- Missing evidence: <trace/counter/proof/report>
3. Proposed action
- Smallest reversible change: <RTL/compiler/runtime/config>
- Expected movement: <throughput/latency/tail/perf-per-watt>
- Regression risk: correctness, security, power, timing, software compatibility
4. Signoff
- Required artifact: Stage-contract specification with pipeline register map and valid/kill timing waveforms for all instruction classes.
- Required owners: CPU microarchitecture lead, RTL implementation owner, timing and physical design owner, verification lead, performance modeling owner
- Final decision: ship, bounded rollout, rollback, or escalate