Rtl P4s Refactor Policy

RTL Refactoring Policy

Refactoring Decision Criteria

• Module >500 lines: consider splitting
• 3+ modules share similar code: extract common module
• Naming inconsistency flagged by rtl-critic: rename pass
• Missing parameterization: add parameters for magic numbers
• Refactoring is selective — not all modules need it

Naming Convention Audit Rules

Refactoring plans MUST include naming convention audit:

• Ports: i_/o_/io_ prefix (NOT suffix _i/_o) — flag violations for correction
• Clocks: clk (single domain) or {domain}_clk (multiple domains) — flag clk_i, clk_sys
• Resets: rst_n (single domain) or {domain}_rst_n (multiple domains) — flag rst_ni
• Instances: u_ prefix — flag missing prefix
• Generates: gen_ prefix — flag missing prefix
• logic only — flag any reg/wire usage

Common refactoring patterns:

• data_i -> i_data, valid_o -> o_valid (suffix to prefix)
• clk_i -> clk or sys_clk (suffix clock to conformant name)
• rst_ni -> rst_n or sys_rst_n (suffix reset to conformant name)
• fifo_inst -> u_fifo (missing instance prefix)
• reg [7:0] data -> logic [7:0] data (reg to logic)

When renaming ports, prefer sv-renamer (https://github.com/babyworm/sv-renamer) when installed:

# Dry-run preview
sv_renamer.py --dir rtl/ --recursive --prefix i_ --dry-run --report json
# Apply + verify equivalence
sv_renamer.py --dir rtl/ --recursive --prefix i_
sv_semantic_diff.py --before original/ --after rtl/  # formal equivalence check

If sv-renamer is not installed, use Grep to find ALL instantiation sites across the codebase and update them in the same task.

Equivalence Proof Policy

• Cosmetic/style-only cleanup: lint + smoke simulation sufficient
• Any change touching combinational/sequential logic, reset, clock enable, or constraints intent: invoke equivalence-checker (RTL-vs-RTL) before completion
• Formal equivalence via SymbiYosys (requires sv2v conversion first):

  sv2v rtl/{module}/*.sv -o rtl/{module}/{module}_v2v.v
  cd formal/ && sby -f {module}.sby   # .sby must reference _v2v.v, not .sv
  

Escalation & Stop Conditions

• Equivalence check fails → revert to original, report diff to user
• Refactoring plan conflicts with uarch spec → pause, flag to user
• For large module splits, update all instantiation sites in the same task to maintain consistency

Final Checklist

• All changed files pass lint (verilator --lint-only -Wall + slang --lint-only)
• Equivalence verified (formal or smoke sim)
• No instantiation sites broken
• Refactoring plan followed exactly
• All port names use i_/o_/io_ prefix (NOT suffix _i/_o)
• All clocks: clk or {domain}_clk — NOT clk_i
• All resets: rst_n or {domain}_rst_n — NOT rst_ni
• All instances: u_ prefix, generates: gen_ prefix
• No reg/wire keywords — logic only