tdraudio: correctly generate silence, clear DAC accumulator

- mem_wait must be enabled on each write
- dcache_hit is never true on a write, so the
  ~dcache_hit clause was always true

tridoracpu/tridoracpu.srcs/dram_bridge.v

@@ -165,7 +165,7 @@ module dram_bridge #(ADDR_WIDTH = 32, WIDTH = 32)
     assign app_wdf_data = { {4{mem_write_data}} };
 
     assign mem_wait =   (dram_read_enable & ~read_inprogress) |
-                        (mem_write_enable & ~dcache_hit & (~app_wdf_rdy | ~app_rdy)) |
+                        (mem_write_enable & (~app_wdf_rdy | ~app_rdy)) |
                         (read_inprogress & ~app_rd_data_valid);
 
     assign app_en = (dram_read_enable & ~read_inprogress) |

tridoracpu/tridoracpu.srcs/tdraudio.v

@@ -1,7 +1,8 @@
 `timescale 1ns / 1ps
 
-// waveform generator module (only pulse wave for now)
-module wavegen #(DATA_WIDTH=32, CLOCK_DIV_WIDTH=22, AMP_WIDTH=16) (
+// waveform generator module (pulse wave or noise)
+module wavegen #(DATA_WIDTH=32, CLOCK_DIV_WIDTH=22,
+    AMP_WIDTH=16, AMP_BIAS=32768) (
         input wire clk,
         input wire reset,
         input wire [1:0] reg_sel,
@@ -18,11 +19,6 @@ module wavegen #(DATA_WIDTH=32, CLOCK_DIV_WIDTH=22, AMP_WIDTH=16) (
     localparam TDRAU_REG_CLK = 1;  /* clock divider register */
     localparam TDRAU_REG_AMP = 2;  /* amplitude (volume) register */
 
-//    localparam LFSR_WIDTH = 15;
-//    localparam LFSR_TAP_IDX_1 = 3;
-//    localparam LFSR_TAP_IDX_2 = 0;
-//    localparam LFSR_INIT = 'h7672;
-
 //    localparam LFSR_WIDTH = 18;
 //    localparam LFSR_TAP_IDX_1 = 17;
 //    localparam LFSR_TAP_IDX_2 = 10;
@@ -138,7 +134,7 @@ module wavegen #(DATA_WIDTH=32, CLOCK_DIV_WIDTH=22, AMP_WIDTH=16) (
     begin
         if (reset)
         begin
-            amp_out <= 0;
+            amp_out <= AMP_BIAS;
             amp_phase <= 1;
         end
         else
@@ -153,7 +149,7 @@ module wavegen #(DATA_WIDTH=32, CLOCK_DIV_WIDTH=22, AMP_WIDTH=16) (
             end
         end
         else
-            amp_out <= 0;
+            amp_out <= AMP_BIAS;
 
         // reset phase bit when enabling the channel
         if (ctl_reg_write && wr_data[0])
@@ -214,6 +210,8 @@ module tdraudio #(DATA_WIDTH=32) (
 
     wire running = chan0_running || chan1_running || chan2_running || chan3_running;
 
+    reg was_running;
+
     assign rd_data = chan0_sel ? chan0_rd_data :
                         chan1_sel ? chan1_rd_data :
                         chan2_sel ? chan2_rd_data :
@@ -247,6 +245,15 @@ module tdraudio #(DATA_WIDTH=32) (
 
     assign shutdown_n = running;
 
+    /* detect shutdown */
+    always @(posedge clk)
+    begin
+        if (reset)
+            was_running <= 0;
+        else
+            was_running <= running;
+    end
+
     /* delta-sigma DAC */
     always @(posedge clk)
     begin
@@ -255,6 +262,9 @@ module tdraudio #(DATA_WIDTH=32) (
         else
         if (running)
             deltasigma_acc <= deltasigma_acc[DAC_WIDTH-1:0] + amp_sum;
+        else
+        if (!running && was_running)  // clear accumulator on shutdown
+            deltasigma_acc <= 0;
     end
 
     /* 1-bit audio output */

tridoracpu/tridoracpu.xpr

@@ -378,10 +378,10 @@
       <Report Name="ROUTE_DESIGN.REPORT_METHODOLOGY" Enabled="1"/>
       <RQSFiles/>
     </Run>
-    <Run Id="impl_1" Type="Ft2:EntireDesign" Part="xc7a35ticsg324-1L" ConstrsSet="constrs_1" Description="To compensate for optimistic delay estimation, add extra delay cost to long distance and high fanout connections. low setting, least pessimistic)" AutoIncrementalCheckpoint="false" WriteIncrSynthDcp="false" State="current" Dir="$PRUNDIR/impl_1" SynthRun="synth_1" IncludeInArchive="true" IsChild="false" GenFullBitstream="true" AutoIncrementalDir="$PSRCDIR/utils_1/imports/impl_1" LaunchOptions="-jobs 6 " AutoRQSDir="$PSRCDIR/utils_1/imports/impl_1" ParallelReportGen="true">
+    <Run Id="impl_1" Type="Ft2:EntireDesign" Part="xc7a35ticsg324-1L" ConstrsSet="constrs_1" Description="Uses multiple algorithms for optimization, placement, and routing to get potentially better results." AutoIncrementalCheckpoint="false" WriteIncrSynthDcp="false" State="current" Dir="$PRUNDIR/impl_1" SynthRun="synth_1" IncludeInArchive="true" IsChild="false" GenFullBitstream="true" AutoIncrementalDir="$PSRCDIR/utils_1/imports/impl_1" LaunchOptions="-jobs 6 " AutoRQSDir="$PSRCDIR/utils_1/imports/impl_1" ParallelReportGen="true">
       <Strategy Version="1" Minor="2">
-        <StratHandle Name="Performance_NetDelay_low" Flow="Vivado Implementation 2024">
-          <Desc>To compensate for optimistic delay estimation, add extra delay cost to long distance and high fanout connections. low setting, least pessimistic)</Desc>
+        <StratHandle Name="Performance_Explore" Flow="Vivado Implementation 2024">
+          <Desc>Uses multiple algorithms for optimization, placement, and routing to get potentially better results.</Desc>
         </StratHandle>
         <Step Id="init_design"/>
         <Step Id="opt_design">
@@ -389,14 +389,14 @@
         </Step>
         <Step Id="power_opt_design"/>
         <Step Id="place_design">
-          <Option Id="Directive">3</Option>
+          <Option Id="Directive">0</Option>
         </Step>
         <Step Id="post_place_power_opt_design"/>
         <Step Id="phys_opt_design">
-          <Option Id="Directive">2</Option>
+          <Option Id="Directive">0</Option>
         </Step>
         <Step Id="route_design">
-          <Option Id="Directive">1</Option>
+          <Option Id="Directive">0</Option>
         </Step>
         <Step Id="post_route_phys_opt_design"/>
         <Step Id="write_bitstream">