RISC-V Design · All levels

Extension Compatibility Policy: Worked Example

Worked Example for Extension Compatibility Policy.

Worked example

Worked Example for Extension Compatibility Policy is anchored on Software portability rate across SKUs and zero-regression compliance against declared ISA profiles.. Convert observations into mechanism-backed decisions with explicit ownership.

A regression flags Software portability rate across SKUs and zero-regression compliance against declared ISA profiles.. Strong closure isolates first failing mechanism, proves causality, applies one bounded change, and validates blast radius.

System view

diagram

RISC-V PIPELINE DIAGRAM - Extension Compatibility Policy

PC -> IF -> ID -> EX -> MEM -> WB
      |     |      |      |      |
  i-cache decode  ALU/BR  LSU    regfile write
              \   |
               +-> branch resolve + redirect

Hot paths:
  - branch + load-use dependencies in ID/EX
  - memory latency stretching MEM stage
  - writeback arbitration for integer/vector units

Focus: keep control hazards predictable

Evidence matrix

diagram

RISC-V EVIDENCE MATRIX - Extension Compatibility Policy

+--------------------------+--------------------------------+--------------------------------+---------------------------+
| Evidence                 | Tells you                      | Does not prove                 | Next action               |
+--------------------------+--------------------------------+--------------------------------+---------------------------+
| perf counter timeline    | where regression appears       | exact mechanism causality      | correlate with trace      |
| decode/control dump      | control intent per instruction | pipeline side-effect ordering  | inspect retire semantics  |
| trap + CSR logs          | privilege/fault behavior       | performance bottleneck alone   | pair with CPI buckets     |
| MMU/TLB walk trace       | translation behavior           | full system QoS impact         | test mixed workloads      |
| post-fix trend graph     | movement after fix             | long-term stability            | run stress matrix         |
+--------------------------+--------------------------------+--------------------------------+---------------------------+

Capture baseline and failing traces under fixed metadata tags.
Classify stage loss and dominant mechanism.
Collect ISA policy document with profile tables, ABI commitments, compiler flags, and conformance regression gates..
Apply one bounded fix with owner signoff.
Run validation matrix and decide ship/rollback.

Practice this lesson