sonic.v

module sonic(
   input clock,
	output trig,
	input echo,
	output reg [32:0] distance
);

reg [32:0] us_counter = 0;
reg _trig = 1'b0;

reg [9:0] one_us_cnt = 0;
wire one_us = (one_us_cnt == 0);

reg [9:0] ten_us_cnt = 0;
wire ten_us = (ten_us_cnt == 0);

reg [21:0] forty_ms_cnt = 0;
wire forty_ms = (forty_ms_cnt == 0);

assign trig = _trig;

always @(posedge clock) begin
	one_us_cnt <= (one_us ? 50 : one_us_cnt) - 1;
	ten_us_cnt <= (ten_us ? 500 : ten_us_cnt) - 1;
	forty_ms_cnt <= (forty_ms ? 2000000 : forty_ms_cnt) - 1;
	
	if (ten_us && _trig)
		_trig <= 1'b0;
	
	if (one_us) begin	
		if (echo)
			us_counter <= us_counter + 1;
		else if (us_counter) begin
			distance <= us_counter / 58;
			us_counter <= 0;
		end
	end
	
   if (forty_ms)
		_trig <= 1'b1;
end

endmodule