Sound output via sigma-delta DAC

boards/tang_nano_9k_hdmi_no_tm1638/board_specific_top.sv

@@ -1,2 +1,3 @@
 `define FORCE_NO_INSTANTIATE_TM1638_BOARD_CONTROLLER_MODULE
+//`define INSTANTIATE_SOUND_DAC_OUTPUT_INTERFACE_MODULE
 `include "../tang_nano_9k_hdmi_tm1638/board_specific_top.sv"

boards/tang_nano_9k_hdmi_tm1638/board_specific_top.sv

@@ -17,6 +17,8 @@
 `define REVERSE_KEY
 `define REVERSE_LED
 
+
+//`define INSTANTIATE_SOUND_DAC_OUTPUT_INTERFACE_MODULE
 //----------------------------------------------------------------------------
 
 module board_specific_top
@@ -428,6 +430,26 @@ module board_specific_top
 
     //------------------------------------------------------------------------
 
+    `ifdef INSTANTIATE_SOUND_DAC_OUTPUT_INTERFACE_MODULE
+        `undef INSTANTIATE_SOUND_OUTPUT_INTERFACE_MODULE
+
+        wire dac_out;
+
+        sigma_delta_dac 
+        #( .MSBI (   7 ), 
+           .INV  ( 1'b0 )
+         ) 
+        SD_DAC
+         ( .DACout( dac_out       ),  //Average Output feeding analog lowpass
+           .DACin ( sound[15 -:8] ),  //DAC input (excess 2**MSBI)
+           .CLK   ( clk           ),
+           .RESET ( rst           )
+         );
+        assign  LARGE_LCD_HS = dac_out;
+        assign  LARGE_LCD_CK = ~dac_out;
+
+    `endif
+
     `ifdef INSTANTIATE_SOUND_OUTPUT_INTERFACE_MODULE
 
         i2s_audio_out
@@ -436,13 +458,13 @@ module board_specific_top
         )
         inst_audio_out
         (
-            .clk      ( clk          ),
-            .reset    ( rst          ),
-            .data_in  ( sound        ),
-            .mclk     ( LARGE_LCD_DE ),
-            .bclk     ( LARGE_LCD_VS ),
-            .lrclk    ( LARGE_LCD_HS ),
-            .sdata    ( LARGE_LCD_CK )
+            .clk      ( clk           ),
+            .reset    ( rst           ),
+            .data_in  ( sound         ),
+            .mclk     ( LARGE_LCD_DE  ),
+            .bclk     ( LARGE_LCD_VS  ),
+            .lrclk    ( LARGE_LCD_HS  ),
+            .sdata    ( LARGE_LCD_CK  )
         );
 
     `endif

peripherals/lab_specific_board_config.svh

@@ -14,6 +14,7 @@
    `define INSTANTIATE_GRAPHICS_INTERFACE_MODULE
    `define INSTANTIATE_MICROPHONE_INTERFACE_MODULE
    `define INSTANTIATE_SOUND_OUTPUT_INTERFACE_MODULE
+//   `define INSTANTIATE_SOUND_DAC_OUTPUT_INTERFACE_MODULE
 
 `endif  // `ifndef LAB_SPECIFIC_BOARD_CONFIG_SVH
 

peripherals/sigma_delta_dac.v

@@ -0,0 +1,36 @@
+//
+// PWM DAC
+//
+// MSBI is the highest bit number. NOT amount of bits!
+//
+// https://github.com/MiSTer-devel/Genesis_MiSTer/blob/master/sys/sigma_delta_dac.v
+//
+
+module sigma_delta_dac #(parameter MSBI=7, parameter INV=1'b1)
+(
+   output reg      DACout, //Average Output feeding analog lowpass
+   input  [MSBI:0] DACin,  //DAC input (excess 2**MSBI)
+   input           CLK,
+   input           RESET
+);
+
+reg [MSBI+2:0] DeltaAdder; //Output of Delta Adder
+reg [MSBI+2:0] SigmaAdder; //Output of Sigma Adder
+reg [MSBI+2:0] SigmaLatch; //Latches output of Sigma Adder
+reg [MSBI+2:0] DeltaB;     //B input of Delta Adder
+
+always @(*) DeltaB = {SigmaLatch[MSBI+2], SigmaLatch[MSBI+2]} << (MSBI+1);
+always @(*) DeltaAdder = DACin + DeltaB;
+always @(*) SigmaAdder = DeltaAdder + SigmaLatch;
+
+always @(posedge CLK or posedge RESET) begin
+   if(RESET) begin
+      SigmaLatch <= 1'b1 << (MSBI+1);
+      DACout <= INV;
+   end else begin
+      SigmaLatch <= SigmaAdder;
+      DACout <= SigmaLatch[MSBI+2] ^ INV;
+   end
+end
+
+endmodule