systemverilog-development

name	SystemVerilog Development
description	This skill should be used when the user asks to 'design a module', 'write SystemVerilog', 'implement an FSM', 'create a pipeline', or works with .sv/.svh/.v/.vh files. Provides modern SV conventions, coding patterns, and synthesizability guidance.
version	1.0.0
globs	["**/*.sv","**/*.svh","**/*.v","**/*.vh"]

SystemVerilog Development

Provide expert guidance for SystemVerilog RTL design following IEEE 1800-2017 standards.

Always Block Conventions

Use modern SystemVerilog constructs:

Purpose	Construct	Pattern
Flip-flops	always_ff	always_ff @(posedge clk or negedge rst_n)
Combinational	always_comb	always_comb begin ... end
Latches (rare)	always_latch	always_latch begin ... end

Signal Types

• Use logic for all signals (replaces wire and reg)
• Use typedef enum logic for state machines
• Use typedef struct packed for grouped signals
• Always specify explicit widths

Reset Convention

Active-low asynchronous reset is the standard pattern:

always_ff @(posedge clk or negedge rst_n) begin
    if (!rst_n) begin
        data_reg <= '0;
    end else begin
        data_reg <= data_next;
    end
end

Port Declarations

Use explicit port typing with ANSI-style declarations:

module example #(
    parameter int WIDTH = 8
) (
    input  logic             clk,
    input  logic             rst_n,
    input  logic [WIDTH-1:0] data_in,
    output logic [WIDTH-1:0] data_out
);

FSM Pattern

Use enumerated types with explicit encoding:

typedef enum logic [1:0] {
    IDLE   = 2'b00,
    ACTIVE = 2'b01,
    DONE   = 2'b10
} state_t;

state_t state_reg, state_next;

always_ff @(posedge clk or negedge rst_n) begin
    if (!rst_n) state_reg <= IDLE;
    else        state_reg <= state_next;
end

always_comb begin
    state_next = state_reg;
    unique case (state_reg)
        IDLE:   if (start) state_next = ACTIVE;
        ACTIVE: if (done)  state_next = DONE;
        DONE:   state_next = IDLE;
        default: state_next = IDLE;
    endcase
end

Handshaking (Valid/Ready)

Standard flow control pattern:

// Producer side
assign valid = data_available;
always_ff @(posedge clk) begin
    if (valid && ready) begin
        // Data accepted, advance to next
    end
end

// Consumer side
assign ready = can_accept;
always_ff @(posedge clk) begin
    if (valid && ready) begin
        captured_data <= data_in;
    end
end

Pipeline Stage

Register data with associated valid signal:

always_ff @(posedge clk or negedge rst_n) begin
    if (!rst_n) begin
        stage1_data  <= '0;
        stage1_valid <= 1'b0;
    end else begin
        stage1_data  <= stage0_data;
        stage1_valid <= stage0_valid;
    end
end

Synthesizability Rules

Ensure all code is synthesizable:

• No initial blocks in RTL (testbench only)
• No # delays in RTL
• No $display or system tasks in RTL
• All signals driven in all paths (no latches unless intended)
• Use unique case or priority case with default