EIE4-FYP/rtl/dacAttenuation.sv

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`default_nettype none
module dacAttenuation
( input var i_clk48 // Runs at 48MHz
, input var i_rst48_n // Active low reset for sys_clk
, input var i_valid // Only update DAC volume when CSRStorage is written to
, input var [7:0] i_atten // 8-bit attenuation control (0x00 = min, 0xFF = max)
, output var o_sel_n // DAC Control bus select (active low)
, output var o_clock // DAC Control bus clock
, output var o_data // DAC Control bus data (serial)
);
logic [7:0] valid;
always_ff @(posedge i_clk48) // Capture when CSTStorage is written to
if (!i_rst48_n) valid <= 8'h00;
else if (i_valid) valid <= 8'hFF;
else valid <= {valid[6:0], 1'b0};
logic [7:0] volume;
always_ff @(posedge i_clk48) // Update volume setting when CSRStorage is written to
if (!i_rst48_n) volume <= 8'h00;
else if (i_valid) volume <= i_atten;
logic [2:0] div_6m;
always_ff @(posedge i_clk48) // Count 6MHz cycle
if (!i_rst48_n) div_6m <= 3'b000;
else div_6m <= div_6m + 1;
always_comb o_clock = div_6m[2]; // Drive DAC Control bus clock at 6MHz
logic [34:0] sel_n;
always_ff @(negedge o_clock) // Update SEL_n on falling edge of CLOCK (As in PCM1780 Datasheet)
if (!i_rst48_n) {o_sel_n, sel_n} <= 36'hFFFFFFFFF;
else if (valid[7]) {o_sel_n, sel_n} <= 36'h0000C0003;
else {o_sel_n, sel_n} <= {sel_n, 1'b1};
logic [34:0] data;
always_ff @(negedge o_clock) // Update DATA on falling edge of CLOCK (As in PCM1780 Datasheet)
if (!i_rst48_n) {o_data, data} <= 36'h000000000;
else if (valid[7]) {o_data, data} <= {8'd16, volume, 2'd0, 8'd17, volume, 2'd0};
else {o_data, data} <= {data, 1'b0};
endmodule