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module top (
input clk
);
reg [7:0] counter = 0;
reg a = 0;
reg b = 1;
reg c;
wire a_fell; assign a_fell = $fell(a, @(posedge clk));
wire a_rose; assign a_rose = $rose(a, @(posedge clk));
wire a_stable; assign a_stable = $stable(a, @(posedge clk));
wire b_fell; assign b_fell = $fell(b, @(posedge clk));
wire b_rose; assign b_rose = $rose(b, @(posedge clk));
wire b_stable; assign b_stable = $stable(b, @(posedge clk));
wire c_fell; assign c_fell = $fell(c, @(posedge clk));
wire c_rose; assign c_rose = $rose(c, @(posedge clk));
wire c_stable; assign c_stable = $stable(c, @(posedge clk));
always @(posedge clk) begin
counter <= counter + 1;
case (counter)
0: begin
assert property ( $fell(a) && !$rose(a) && !$stable(a));
assert property (!$fell(b) && $rose(b) && !$stable(b));
assert property (!$fell(c) && !$rose(c) && $stable(c));
a <= 1; b <= 1; c <= 1;
end
1: begin a <= 0; b <= 1; c <= 'x; end
2: begin
assert property ( $fell(a) && !$rose(a) && !$stable(a));
assert property (!$fell(b) && !$rose(b) && $stable(b));
assert property (!$fell(c) && !$rose(c) && !$stable(c));
a <= 0; b <= 0; c <= 0;
end
3: begin a <= 0; b <= 1; c <= 'x; end
4: begin
assert property (!$fell(a) && !$rose(a) && $stable(a));
assert property (!$fell(b) && $rose(b) && !$stable(b));
assert property (!$fell(c) && !$rose(c) && !$stable(c));
a <= 'x; b <= 'x; c <= 'x;
end
5: begin a <= 0; b <= 1; c <= 'x; counter <= 0; end
endcase;
end
endmodule
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