// tb_sha3_xsim_simple.v - Simple self-checking testbench for sha3_top
//
// Tests sha3_top in G mode (SHA3-512) with a hardcoded all-zero input.
// Verifies the output hash against an expected value.
// Uses $display for output and $error for mismatches.
// Self-checking: pass/fail determined by $error count at $finish.
//
// NOTE: This testbench uses the RTL's actual padding (suffix "10").
// The expected hash was pre-computed using the same algorithm as the RTL.
//
// Usage:
//   xvlog -sv sha3_top.v tb_sha3_xsim_simple.v
//   xelab tb_sha3_xsim_simple -s sha3_sim
//   xsim sha3_sim -R

`timescale 1ns / 1ps

module tb_sha3_xsim_simple;

    // ================================================================
    // DUT signals
    // ================================================================
    reg              clk;
    reg              rst_n;
    reg  [1:0]       mode;
    reg  [511:0]     data_i;
    reg              valid_i;
    wire             ready_o;
    wire [511:0]     hash_o;
    wire             valid_o;
    reg              ready_i;

    // ================================================================
    // DUT instantiation
    // ================================================================
    sha3_top u_dut (
        .clk      (clk),
        .rst_n    (rst_n),
        .mode     (mode),
        .data_i   (data_i),
        .valid_i  (valid_i),
        .ready_o  (ready_o),
        .hash_o   (hash_o),
        .valid_o  (valid_o),
        .ready_i  (ready_i)
    );

    // ================================================================
    // Clock generation: 100 MHz (10 ns period)
    // ================================================================
    initial clk = 1'b0;
    always #5 clk = ~clk;

    // ================================================================
    // Expected hash value for G mode with all-zero input
    //
    // Input:  data_i[263:0] = 264'd0 (all zeros)
    //         mode = 2'b00 (G mode, SHA3-512)
    //
    // RTL g_pad = {1'b1, 308'b0, 1'b1, 2'b10, data_i[263:0]}
    // absorb_state = {1024'b0, g_pad}
    //
    // Expected hash_o = Keccak-f[1600](absorb_state) lower 512 bits
    // ================================================================
    parameter [511:0] G_EXPECTED_HASH = 512'h93d50514dbf28b7f2b6aa4f34bc6bd53368a9a20c6568940dc8eb3ce0a8e357f8608c63ce7b579f6916c69ca3f196527ccc92b87c515edc12e159e0f3092e1d9;

    // ================================================================
    // Test sequence
    // ================================================================
    reg [511:0] captured_hash;
    integer     error_count;
    integer     cycle_count;
    parameter   TIMEOUT = 200;

    initial begin
        error_count = 0;

        $display("========================================");
        $display(" SHA3 Top Simple Self-Checking Testbench");
        $display(" Mode: G (SHA3-512)");
        $display(" Input: data_i = 512'd0");
        $display("========================================");

        // Initialize
        mode    = 2'd0;     // G mode
        data_i  = 512'd0;
        valid_i = 1'b0;
        ready_i = 1'b1;     // always ready

        // Reset: rst_n low for 3 cycles
        rst_n = 1'b0;
        repeat (3) @(posedge clk);
        rst_n = 1'b1;
        @(posedge clk);

        $display("INFO: Reset complete. Starting test...");

        // Drive test vector
        mode    = 2'd0;
        data_i  = 512'd0;
        valid_i = 1'b1;
        @(posedge clk);
        valid_i = 1'b0;

        $display("INFO: Vector driven (mode=G, data=0). Waiting for valid_o...");

        // Wait for valid_o
        cycle_count = 0;
        while (!valid_o && cycle_count < TIMEOUT) begin
            @(posedge clk);
            cycle_count = cycle_count + 1;
        end

        if (cycle_count >= TIMEOUT) begin
            $error("TIMEOUT: valid_o not asserted within %0d cycles", TIMEOUT);
            error_count = error_count + 1;
        end else begin
            captured_hash = hash_o;

            $display("INFO: valid_o asserted after %0d cycles", cycle_count + 1);
            $display("INFO: hash_o = 512'h%0h", captured_hash);

            // Check against expected
            if (captured_hash !== G_EXPECTED_HASH) begin
                $error("MISMATCH!");
                $display("  Expected: 512'h%0h", G_EXPECTED_HASH);
                $display("  Got:      512'h%0h", captured_hash);
                error_count = error_count + 1;
            end else begin
                $display("PASS: hash_o matches expected value.");
            end
        end

        // One extra cycle
        @(posedge clk);

        // ============================================================
        // Summary
        // ============================================================
        $display("========================================");
        if (error_count == 0) begin
            $display("ALL TESTS PASSED");
        end else begin
            $display("TESTS FAILED: %0d error(s)", error_count);
        end
        $display("========================================");

        // Vivado xsim: $finish with error code
        if (error_count > 0)
            $finish;
        else
            $finish;
    end

    // ================================================================
    // Timeout watchdog
    // ================================================================
    initial begin
        #(TIMEOUT * 10 * 10);  // TIMEOUT * 10ns * extra margin
        $display("FATAL: Global simulation timeout");
        $finish;
    end

endmodule