X-Git-Url: http://git.joshuawise.com/fpgaboy.git/blobdiff_plain/b4f3ac35e69b7d5adf57959902abe2a104b42f4f..6ba4cfea4b24fdd898e90ebd55e95ad43d5d21d4:/Sound2.v

diff --git a/Sound2.v b/Sound2.v
new file mode 100644
index 0000000..fa5e5e7
--- /dev/null
+++ b/Sound2.v
@@ -0,0 +1,75 @@
+`define ADDR_NR21 16'hFF16
+`define ADDR_NR22 16'hFF17
+`define ADDR_NR23 16'hFF18
+`define ADDR_NR24 16'hFF19
+
+module Sound2(
+	input core_clk,
+	input wr,
+	input rd,
+	input [15:0] addr,
+	inout [7:0] data,
+	input cntclk,
+	input lenclk,
+	input en,
+	output [3:0] snd_data
+	);
+
+	/* can be optimized as register file */
+	reg [7:0] nr21, nr22, nr23, nr24;
+	reg [10:0] counter = 0;
+	reg [4:0] lencnt = 0;
+	reg [3:0] delta = 4'b1111;
+	reg [2:0] dutycnt;
+	reg [3:0] snd_out = 0;
+
+	assign snd_data = en ? snd_out : 0;
+
+	assign data = rd ?
+	                 addr == `ADDR_NR21 ? nr21 :
+	                 addr == `ADDR_NR22 ? nr22 :
+	                 addr == `ADDR_NR23 ? nr23 :
+	                 addr == `ADDR_NR24 ? nr24 : 8'bzzzzzzzz
+	              : 8'bzzzzzzzz;
+
+	always @ (negedge core_clk) begin
+		if(en && wr) begin
+			case(addr)
+			`ADDR_NR21: nr21 <= data;
+			`ADDR_NR22: nr22 <= data;
+			`ADDR_NR23: nr23 <= data;
+			`ADDR_NR24: nr24 <= data;
+			endcase
+		end
+		else if(!en) begin
+			nr21 <= 8'h3F;
+			nr22 <= 8'h00;
+			nr23 <= 8'hFF;
+			nr24 <= 8'hBF;
+		end
+	end
+
+	always @ (posedge cntclk) begin
+		if(counter)
+			counter <= counter - 1;
+		else begin
+			counter <= ~{nr24[2:0],nr23} + 1;  /* possible A */
+			dutycnt <= dutycnt + 1;
+		end
+
+		case (nr21[7:6])
+		2'b00: snd_out <= dutycnt ? 0 : delta;   /* probable A */
+		2'b01: snd_out <= (dutycnt[2:1] == 2'b0) ? delta : 0;
+		2'b10: snd_out <= dutycnt[2] ? delta : 0;
+		2'b11: snd_out <= (dutycnt[2:1] == 2'b0) ? 0 : delta;
+		endcase
+	end
+
+	always @ (posedge lenclk) begin
+		if(lencnt)
+			lencnt <= lencnt - 1;            /* possible A */
+		else
+			lencnt <= ~nr21[4:0] + 1;
+	end
+
+endmodule