Signals in Verilog

Here’s an idiomatic Verilog example demonstrating a concept similar to signal handling:

module signal_handler (
  input wire clk,
  input wire reset,
  input wire signal_interrupt,
  input wire signal_terminate,
  output reg [7:0] status
);

  // Define states
  localparam IDLE = 2'b00;
  localparam RUNNING = 2'b01;
  localparam INTERRUPTED = 2'b10;
  localparam TERMINATED = 2'b11;

  reg [1:0] state;
  reg [1:0] next_state;

  // State transition logic
  always @(posedge clk or posedge reset) begin
    if (reset)
      state <= IDLE;
    else
      state <= next_state;
  end

  // Next state and output logic
  always @(*) begin
    next_state = state;
    status = 8'h00;

    case (state)
      IDLE: begin
        status = 8'h01;
        if (signal_interrupt || signal_terminate)
          next_state = RUNNING;
      end

      RUNNING: begin
        status = 8'h02;
        if (signal_interrupt)
          next_state = INTERRUPTED;
        else if (signal_terminate)
          next_state = TERMINATED;
      end

      INTERRUPTED: begin
        status = 8'h03;
        next_state = IDLE;
      end

      TERMINATED: begin
        status = 8'h04;
        // Stay in TERMINATED state
      end

      default: next_state = IDLE;
    endcase
  end

endmodule

This Verilog module demonstrates a concept similar to signal handling in a hardware context. Let’s break down the code and its functionality:

1. The module signal_handler has inputs for clock (clk), reset (reset), and two signals (signal_interrupt and signal_terminate). It outputs an 8-bit status register.

2. We define four states using localparams: IDLE, RUNNING, INTERRUPTED, and TERMINATED.

3. The module uses a two-process state machine model:

   • The first always block handles state transitions on the rising edge of the clock or reset.
   • The second always block is combinational and determines the next state and output based on the current state and inputs.

4. The state machine behaves as follows:

   • In the IDLE state, it waits for either signal to transition to the RUNNING state.
   • In the RUNNING state, it checks for signal_interrupt or signal_terminate.
   • If interrupted, it goes to the INTERRUPTED state and then back to IDLE.
   • If terminated, it goes to the TERMINATED state and stays there.

5. The status output changes based on the current state, providing information about the module’s status.

To simulate this Verilog module, you would typically create a testbench that instantiates the module and provides clock and input signals. You can use a Verilog simulator like ModelSim, Icarus Verilog, or Verilator to run the simulation.

This example demonstrates how to handle different signals in a hardware design, which is conceptually similar to signal handling in software, but implemented using hardware description language constructs like state machines and synchronous logic.