Base Integer ISA (RV32I and RV64I) Execution Model: Mechanism

Mechanism to understand

Mechanism 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.

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.

• Name first failing path and trigger condition.

• Prove path loss with one measurable artifact.

• Assign owner who can deliver smallest reversible fix.

Pipeline mechanism sketch

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

Decode intent map

DECODE CONTROL MAP - Base Integer ISA (RV32I and RV64I) Execution Model

opcode/funct3/funct7      controls asserted
-----------------------   ---------------------------------------
LUI / AUIPC               rd_write, imm_select(U), alu_add_pc
JAL / JALR                rd_write, pc_redirect, link_write
BRANCH                    cmp_enable, branch_type, pc_redirect
LOAD                      mem_read, rd_write, wb_sel(memory)
STORE                     mem_write, store_size, addr_calc
OP-IMM                    alu_enable, imm_select(I), rd_write
OP                        alu_enable, src2_reg, rd_write
SYSTEM / CSR              csr_readwrite, trap_check, privilege_gate
VECTOR (V extension)      vdecode, lane_mask, vtype_update