systemverilog-lint-fixing

name	SystemVerilog Lint Fixing
description	This skill should be used when the user mentions 'lint error', 'width mismatch', 'inferred latch', 'undriven signal', 'fix warnings', 'Verilator error', 'WIDTHTRUNC', 'BLKSEQ', or asks to 'check my code' or 'find errors'. Provides error-specific fix patterns for SystemVerilog lint issues.
version	1.0.0

SystemVerilog Lint Fix Patterns

Error-specific fix patterns for common SystemVerilog lint issues.

WIDTHTRUNC / WIDTHEXPAND

Message: Width mismatch in assignment

Diagnosis: Signal widths don't match between source and destination.

Fixes:

// Truncation (wide to narrow) - explicit slice
logic [15:0] wide;
logic [7:0]  narrow;
assign narrow = wide[7:0];

// Extension (narrow to wide) - zero extend
assign wide = {8'b0, narrow};

// Sign extension
assign wide = {{8{narrow[7]}}, narrow};

// Using $bits for dynamic width
assign narrow = wide[$bits(narrow)-1:0];

LATCH

Message: Latch inferred for signal

Diagnosis: Combinational block doesn't assign signal in all paths.

Fixes:

// Add default assignment at block start
always_comb begin
    out = '0;  // Default prevents latch
    if (sel) begin
        out = in_a;
    end
    // No else needed - default covers it
end

// Complete case statement
always_comb begin
    unique case (sel)
        2'b00: out = a;
        2'b01: out = b;
        2'b10: out = c;
        default: out = '0;  // Explicit default
    endcase
end

UNDRIVEN

Message: Signal is not driven

Diagnosis: Signal declared but never assigned a value.

Fixes:

// Option 1: Connect to appropriate source
assign undriven_sig = source_sig;

// Option 2: Remove if truly unused
// Delete the declaration

// Option 3: Tie off if intentionally unused
assign unused_input = '0;

UNUSED

Message: Signal/variable is unused

Fixes:

// Option 1: Remove declaration entirely

// Option 2: Use lint pragma for intentional cases
/* verilator lint_off UNUSED */
logic debug_signal;
/* verilator lint_on UNUSED */

// Option 3: Prefix with underscore (convention)
logic _unused_port;

CASEINCOMPLETE

Message: Case statement does not cover all values

Fix: Add default case

unique case (state)
    IDLE:   next_state = start ? ACTIVE : IDLE;
    ACTIVE: next_state = done ? DONE : ACTIVE;
    DONE:   next_state = IDLE;
    default: next_state = IDLE;  // Required
endcase

BLKSEQ

Message: Blocking assignment in sequential block

Fix: Use non-blocking for sequential logic

// Wrong
always_ff @(posedge clk) begin
    data = new_data;  // Blocking - bad
end

// Correct
always_ff @(posedge clk) begin
    data <= new_data;  // Non-blocking - good
end

COMBDLY

Message: Delayed assignment in combinational block

Fix: Remove delays from combinational logic

// Wrong
always_comb begin
    out = #1 in_a & in_b;  // Delay - not synthesizable
end

// Correct
always_comb begin
    out = in_a & in_b;
end

MULTIDRIVEN

Message: Signal driven from multiple always blocks

Fix: Consolidate drivers or use separate signals

// Wrong - multiple drivers
always_ff @(posedge clk) data <= a;
always_ff @(posedge clk) data <= b;

// Correct - single driver with mux
always_ff @(posedge clk) begin
    data <= sel ? a : b;
end

Fix Workflow

1. Read error message and line number
2. Identify error category from above
3. Apply appropriate fix pattern
4. Re-run lint to verify
5. Check for cascading errors from the fix