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Base Integer ISA (RV32I and RV64I) Execution Model: Debug Playbook

Debug Playbook for Base Integer ISA (RV32I and RV64I) Execution Model.

Debug playbook

Debug Playbook for Base Integer ISA (RV32I and RV64I) Execution Model is anchored on Instruction count mix, branch density, and CPI breakdown by ALU, load/store, branch, and control-transfer classes.. Convert observations into mechanism-backed decisions with explicit ownership.

  1. Freeze workload seed, binary, compiler, firmware, and platform setup.

  2. Find earliest persistent mechanism failure in the timeline.

  3. Build one reduced reproducer for dominant hypothesis.

  4. Patch minimal fix with explicit rollback gate.

  5. Rerun correctness + performance + power matrix.

Decision tree

diagram
ROOT CAUSE TREE - Base Integer ISA (RV32I and RV64I) Execution Model

Instruction count mix, branch density, and CPI breakdown by ALU, load/store, branch, and control-transfer classes. regressed
          |
   reproducible on fixed seed?
      /                 \
    no                   yes
    |                     |
env/tool drift       first failing domain?
                     /        |         \
                  decode    execute    memory/MMU
                    |         |            |
               control map  bypass/FU   TLB/walk/perm
                    |
         privilege/CSR side effects checked?

Stop at first confirmed mechanism, then assign explicit owner + fix proof.

Review memo template

diagram
RISC-V REVIEW MEMO - RISC-V ISA Fundamentals / Base Integer ISA (RV32I and RV64I) Execution Model

1. Symptom
   - Failing metric: Instruction count mix, branch density, and CPI breakdown by ALU, load/store, branch, and control-transfer classes.
   - Failing workload slice: <name>
   - Triggering mode: <privilege/virtualization/interrupt/cache/boot>
   - Build and runtime tags: <toolchain/firmware/RTL revision>

2. Mechanism hypothesis
   - Primary mechanism: The base integer ISA defines a clean load/store architecture: arithmetic and logical operations act only on registers, while memory is accessed through explicit load and store instructions. RV32I and RV64I share the same core design philosophy, with RV64I widening register and address operations and adding word-specific variants for 32-bit subword behavior. The ISA keeps the architectural state intentionally small and regular (32 integer registers plus program counter), making decode and hazard handling straightforward in simple pipelines while still scaling to out-of-order designs. Control flow is formed by conditional branches and jumps with well-defined PC-relative semantics, and the system model separates user-visible instructions from privileged behavior so implementations can reuse the base frontend across microcontrollers, Linux-capable cores, and accelerator-adjacent control processors.
   - 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: Base ISA execution map covering instruction classes, dataflow constraints, and implementation implications from single-cycle to superscalar pipelines.
   - Required owners: CPU microarchitecture lead, compiler backend owner, verification lead, performance modeling owner, firmware and bring-up owner
   - Final decision: ship, bounded rollout, rollback, or escalate
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