vga_vtim.v

用来实现VGA发生时序

/////////////////////////////////////////////////////////////////////

`include "timescale.v"
//synopsys translate_on

module vga_vtim(clk, ena, rst,
// 	Tsync, Tgdel, Tgate, Tlen, 
	Sync, Gate, Done);
	// inputs & outputs
	input clk; // master clock
	input ena; // count enable
	input rst; // synchronous active high reset
/*
	input [ 7:0] Tsync; // sync duration
	input [ 7:0] Tgdel; // gate delay
	input [15:0] Tgate; // gate length
	input [15:0] Tlen;  // line time / frame time
*/
	output Sync; // synchronization pulse
	output Gate; // gate
	output Done; // done with line/frame
	reg Sync;
	reg Gate;
	reg Done;

	//
	// module body
	//

	// generate timing statemachine
	reg  [15:0] cnt, cnt_len;
	wire [16:0] cnt_nxt, cnt_len_nxt;
	wire        cnt_done, cnt_len_done;

	assign cnt_nxt = {1'b0, cnt} -17'h1;
	assign cnt_done = cnt_nxt[16];

	assign cnt_len_nxt = {1'b0, cnt_len} -17'h1;
	assign cnt_len_done = cnt_len_nxt[16];

	reg [4:0] state;
	
	parameter [ 7:0] Tsync = 8'h0; // sync duration
	parameter [ 7:0] Tgdel = 8'h0; // gate delay
	parameter [15:0] Tgate = 16'h0; // gate length
	parameter [15:0] Tlen  = 16'h0;  // line time / frame time

	
	parameter [4:0] idle_state = 5'b00001;
	parameter [4:0] sync_state = 5'b00010;
	parameter [4:0] gdel_state = 5'b00100;
	parameter [4:0] gate_state = 5'b01000;
	parameter [4:0] len_state  = 5'b10000;

	always @(posedge clk)
	  if (rst)
	    begin
	        state   <= #1 idle_state;
	        cnt     <= #1 16'h0;
	        cnt_len <= #1 16'b0;
	        Sync    <= #1 1'b0;
	        Gate    <= #1 1'b0;
	        Done    <= #1 1'b0;
	    end
	  else if (ena)
	    begin
	        cnt     <= #1 cnt_nxt[15:0];
	        cnt_len <= #1 cnt_len_nxt[15:0];

	        Done    <= #1 1'b0;

	        case (state) // synopsys full_case parallel_case
	          idle_state:
	            begin
	                state   <= #1 sync_state;
	                cnt     <= #1 Tsync;
	                cnt_len <= #1 Tlen;

	                Sync    <= #1 1'b1;
	            end

	          sync_state:
	            if (cnt_done)
	              begin
	                  state <= #1 gdel_state;
	                  cnt   <= #1 Tgdel;

	                  Sync  <= #1 1'b0;
	              end

	          gdel_state:
	            if (cnt_done)
	              begin
	                  state <= #1 gate_state;
	                  cnt   <= #1 Tgate;

	                  Gate  <= #1 1'b1;
	              end

	          gate_state:
	            if (cnt_done)
	              begin
	                  state <= #1 len_state;

	                  Gate  <= #1 1'b0;
	              end

	          len_state:
	            if (cnt_len_done)
	              begin
	                  state   <= #1 sync_state;
	                  cnt     <= #1 Tsync;
	                  cnt_len <= #1 Tlen;

	                  Sync    <= #1 1'b1;
	                  Done    <= #1 1'b1;
	              end

	        endcase
	    end
endmodule