RISC-V Design · All levels

Base Integer ISA (RV32I and RV64I) Execution Model: Worked Example

Worked Example for Base Integer ISA (RV32I and RV64I) Execution Model.

Worked example

Worked Example 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.

A regression flags Instruction count mix, branch density, and CPI breakdown by ALU, load/store, branch, and control-transfer classes.. Strong closure isolates first failing mechanism, proves causality, applies one bounded change, and validates blast radius.

System view

diagram

RISC-V PIPELINE DIAGRAM - Base Integer ISA (RV32I and RV64I) Execution Model

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 - Base Integer ISA (RV32I and RV64I) Execution Model

+--------------------------+--------------------------------+--------------------------------+---------------------------+
| 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 Base ISA execution map covering instruction classes, dataflow constraints, and implementation implications from single-cycle to superscalar pipelines..
Apply one bounded fix with owner signoff.
Run validation matrix and decide ship/rollback.

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