108 lines
3.5 KiB
Systemverilog
108 lines
3.5 KiB
Systemverilog
// DESCRIPTION: Verilator: Verilog Test module
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//
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// This file ONLY is placed under the Creative Commons Public Domain
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// SPDX-FileCopyrightText: 2026
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// SPDX-License-Identifier: CC0-1.0
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// verilog_format: off
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`define stop $stop
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`define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d: got=%0d exp=%0d\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0);
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// verilog_format: on
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// Test constraint with conditional dist operator
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class DistScalar;
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rand bit [7:0] x;
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rand bit mode; // 0: favor zeros (weight 3:1), 1: favor max (weight 1:3)
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constraint c {
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if (mode) {
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x dist { 8'd0 := 1, 8'd255 := 3 }; // Favor 255
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} else {
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x dist { 8'd0 := 3, 8'd255 := 1 }; // Favor 0
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}
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}
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function void display(int trial);
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$display("Trial %0d: mode=%b, x=%0d (0x%02x)", trial, mode, x, x);
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endfunction
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endclass
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module t;
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DistScalar obj;
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int mode1_zeros = 0; // Count of zeros when mode=1 (favor 255)
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int mode1_maxes = 0; // Count of 255s when mode=1 (favor 255)
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int mode0_zeros = 0; // Count of zeros when mode=0 (favor 0)
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int mode0_maxes = 0; // Count of 255s when mode=0 (favor 0)
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int mode1_trials = 0; // Total trials with mode=1
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int mode0_trials = 0; // Total trials with mode=0
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// Verify distribution ratio matches expected range
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function void check_distribution(int trials, int match_count, string match_name,
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int expected_pct, string mode_name);
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int actual_pct;
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int lower_bound;
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int upper_bound;
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if (trials <= 0) return;
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actual_pct = (match_count * 100) / trials;
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$display(" %s %s ratio: %0d/%0d = %0d%% (expected ~%0d%%)",
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mode_name, match_name, match_count, trials, actual_pct, expected_pct);
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// Allow +/-15% deviation from expected ratio
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lower_bound = expected_pct - 15;
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upper_bound = expected_pct + 15;
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if (actual_pct >= lower_bound && actual_pct <= upper_bound) begin
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$display("Distribution OK");
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end else begin
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$display("WARNING: Distribution appears off (expected %0d+/-15%%)", expected_pct);
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$stop;
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end
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endfunction
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initial begin
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int p;
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obj = new;
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// Run multiple trials to verify distribution
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for (int i = 0; i < 1000; i++) begin
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p = obj.randomize();
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`checkd(p, 1);
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if (i < 10) obj.display(i);
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// Track distribution based on mode value
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if (obj.mode) begin
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mode1_trials++;
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if (obj.x == 8'd0) mode1_zeros++;
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else if (obj.x == 8'd255) mode1_maxes++;
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end else begin
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mode0_trials++;
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if (obj.x == 8'd0) mode0_zeros++;
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else if (obj.x == 8'd255) mode0_maxes++;
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end
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end
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$display("");
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$display("Statistics after 1000 trials:");
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$display(" Mode 1 (favor 255): trials=%0d, zeros=%0d, maxes=%0d",
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mode1_trials, mode1_zeros, mode1_maxes);
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$display(" Mode 0 (favor 0): trials=%0d, zeros=%0d, maxes=%0d",
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mode0_trials, mode0_zeros, mode0_maxes);
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$display("");
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$display("Distribution Verification:");
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// Mode 1: x dist { 0 := 1, 255 := 3 } means 25% for 0, 75% for 255
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check_distribution(mode1_trials, mode1_maxes, "maxes", 75, "Mode 1");
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// Mode 0: x dist { 0 := 3, 255 := 1 } means 75% for 0, 25% for 255
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check_distribution(mode0_trials, mode0_zeros, "zeros", 75, "Mode 0");
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$display("");
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$display("PASSED: Conditional dist constraint test");
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$write("*-* All Finished *-*\n");
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$finish;
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end
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endmodule
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