MacPlus_MiSTer/sys/audio_out.v

module audio_out
#(
	parameter CLK_RATE = 50000000
)
(
	input        reset,
	input        clk,

	//0 - 48KHz, 1 - 96KHz
	input        sample_rate,

	input [15:0] left_in,
	input [15:0] right_in,

	// I2S
	output       i2s_bclk,
	output       i2s_lrclk,
	output       i2s_data,

	// SPDIF
   output       spdif,

	// Sigma-Delta DAC
	output       dac_l,
	output       dac_r
);

localparam AUDIO_RATE = 48000;
localparam AUDIO_DW = 16;

localparam CE_RATE = AUDIO_RATE*AUDIO_DW*8;
localparam FILTER_DIV = (CE_RATE/(AUDIO_RATE*32))-1;

wire [31:0] real_ce = sample_rate ? {CE_RATE[30:0],1'b0} : CE_RATE[31:0];

reg mclk_ce;
always @(posedge clk) begin
	reg [31:0] cnt;

	mclk_ce <= 0;
	cnt = cnt + real_ce;
	if(cnt >= CLK_RATE) begin
		cnt = cnt - CLK_RATE;
		mclk_ce <= 1;
	end
end

reg i2s_ce;
always @(posedge clk) begin
	reg div;
	i2s_ce <= 0;
	if(mclk_ce) begin
		div <= ~div;
		i2s_ce <= div;
	end
end

reg lpf_ce;
always @(posedge clk) begin
	integer div;
	lpf_ce <= 0;
	if(mclk_ce) begin
		div <= div + 1;
		if(div == FILTER_DIV) begin
			div <= 0;
			lpf_ce <= 1;
		end
	end
end

i2s i2s
(
	.reset(reset),

	.clk(clk),
	.ce(i2s_ce),

	.sclk(i2s_bclk),
	.lrclk(i2s_lrclk),
	.sdata(i2s_data),

	.left_chan(al),
	.right_chan(ar)
);

spdif toslink
(
	.rst_i(reset),

	.clk_i(clk),
	.bit_out_en_i(mclk_ce),

	.sample_i({ar,al}),
	.spdif_o(spdif)
);

sigma_delta_dac #(15) sd_l
(
	.CLK(clk),
	.RESET(reset),
	.DACin({~al[15], al[14:0]}),
	.DACout(dac_l)
);

sigma_delta_dac #(15) sd_r
(
	.CLK(clk),
	.RESET(reset),
	.DACin({~ar[15], ar[14:0]}),
	.DACout(dac_r)
);

wire [15:0] al, ar;
lpf_aud lpf_l
(
   .CLK(clk),
   .CE(lpf_ce),
   .IDATA(left_in),
   .ODATA(al)
);

lpf_aud lpf_r
(
   .CLK(clk),
   .CE(lpf_ce),
   .IDATA(right_in),
   .ODATA(ar)
);

endmodule

module lpf_aud
(
   input         CLK,
   input         CE,
   input  [15:0] IDATA,
   output reg [15:0] ODATA
);

reg [511:0] acc;
reg [20:0] sum;

always @(*) begin
	integer i;
	sum = 0;
	for (i = 0; i < 32; i = i+1) sum = sum + {{5{acc[(i*16)+15]}}, acc[i*16 +:16]};
end

always @(posedge CLK) begin
	if(CE) begin
		acc <= {acc[495:0], IDATA};
		ODATA <= sum[20:5];
	end
end

endmodule