RISC-V Design · All levels

Base Integer ISA (RV32I and RV64I) Execution Model: Theory Deep Dive

Theory Deep Dive for Base Integer ISA (RV32I and RV64I) Execution Model.

Theory deep dive

Theory Deep Dive 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.

Theory matters when it predicts engineering outcomes. Tie abstract ISA and microarchitecture concepts to measurable behavior in trace and counter data.

Pipeline model

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

Privilege model

diagram

PRIVILEGE MODE STACK - Base Integer ISA (RV32I and RV64I) Execution Model

            +------------------------------+
            | Machine mode (M)             |
            | firmware, PMP, trap root     |
            +---------------+--------------+
                            |
                    delegated traps
                            v
            +------------------------------+
            | Supervisor mode (S)          |
            | kernel, page tables, drivers |
            +---------------+--------------+
                            |
                    ecall / syscall
                            v
            +------------------------------+
            | User mode (U)                |
            | applications, libraries      |
            +------------------------------+

Key rule: each upward transition records cause + PC in trap CSRs.

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