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Compressed ISA and Extension Landscape Overview: Debug Playbook

Debug Playbook for Compressed ISA and Extension Landscape Overview.

Debug playbook

Debug Playbook for Compressed ISA and Extension Landscape Overview is anchored on Code-size reduction from C extension, extension utilization rate, and performance-per-watt impact by workload segment.. 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 - Compressed ISA and Extension Landscape Overview

Code-size reduction from C extension, extension utilization rate, and performance-per-watt impact by workload segment. 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 / Compressed ISA and Extension Landscape Overview

1. Symptom
   - Failing metric: Code-size reduction from C extension, extension utilization rate, and performance-per-watt impact by workload segment.
   - Failing workload slice: <name>
   - Triggering mode: <privilege/virtualization/interrupt/cache/boot>
   - Build and runtime tags: <toolchain/firmware/RTL revision>

2. Mechanism hypothesis
   - Primary mechanism: RISC-V grows from a stable base through modular extensions, with common standards such as M (integer multiply/divide), A (atomics), F/D (floating point), and C (compressed instructions). The compressed extension introduces 16-bit encodings for frequently used operations, improving instruction-cache density and fetch bandwidth efficiency at the cost of added decode expansion logic. Extension selection is product-driven: microcontrollers may prioritize code density and deterministic timing, while application-class cores adopt richer arithmetic, vector, and virtualization capabilities. A key architecture responsibility is maintaining a coherent feature profile across hardware, compiler flags, runtime detection, and operating system expectations. Teams must also manage compatibility boundaries between standard and custom extensions so software remains portable, test coverage remains tractable, and compliance claims remain defensible across silicon revisions.
   - 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: Extension profile matrix mapping C/M/A/F/D and optional platform features to software requirements, toolchain settings, and compliance tests.
   - Required owners: SoC architecture lead, CPU microarchitecture lead, compiler and toolchain owner, OS and platform software owner, product and ecosystem owner
   - Final decision: ship, bounded rollout, rollback, or escalate
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