Forwarding Network and Stall Control for Data Hazards: Mechanism

Mechanism to understand

Mechanism for Forwarding Network and Stall Control for Data Hazards is anchored on RAW hazard coverage percentage with zero incorrect-commit events and minimum load-use stall cycles per kilo-instruction.. Convert observations into mechanism-backed decisions with explicit ownership.

Data hazards occur when a consumer instruction needs a value that has not reached the register file yet. Forwarding (bypass) paths resolve most ALU-to-ALU and ALU-to-branch dependencies by routing results from EX/MEM or MEM/WB back into EX operand muxes with priority logic for youngest producer wins. Some cases still require stalls, especially load-use hazards when data becomes valid only after memory response timing; hazard detection must freeze PC and IF/ID while injecting a controlled bubble into downstream control. Correctness depends on tight coordination between forwarding select logic, stall gating, and kill handling so that wrong-path or excepting instructions never source or write stale values. Robust implementations pair dependency matrices with constrained-random instruction streams and assertion-based checks on operand freshness.

• 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 - Forwarding Network and Stall Control for Data Hazards

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 - Forwarding Network and Stall Control for Data Hazards

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