add debounce filter to cassette input

rtl/aci.v

@@ -21,7 +21,7 @@ module ACI (
 
 	wire io_range = addr >= 16'hC000 && addr <= 16'hC0FF;
 	
-   wire [7:0] read_addr = io_range ? { addr[7:1], addr[0] & tape_in } : addr[7:0];
+   wire [7:0] read_addr = io_range ? { addr[7:1], addr[0] & debounced_tape_in } : addr[7:0];
 		
    always @(posedge clk) begin
 
@@ -30,6 +30,24 @@ module ACI (
 
       dout <= rom_data[read_addr];
    end
+	
+	// filters tape_in with anti bounce 
+	wire debounced_tape_in = last_tape_in;
+	reg last_tape_in;
+	reg [31:0] bounce_cnt;
+	localparam bounce_max = 3579;   // 57272719 / 3579 = ~16 KHz max
+	
+	always @(posedge clk) begin
+		if(tape_in != last_tape_in) begin			
+			if(bounce_cnt < bounce_max) begin
+				bounce_cnt <= bounce_cnt + 1;
+			end
+			else begin
+				bounce_cnt <= 0;				
+				last_tape_in = tape_in;		
+			end
+		end
+	end
 
 endmodule