Fixed noise LFSR drivers

rejunity · Sep 18, 2023 · e2fc6a2 · e2fc6a2
1 parent a5cabc8
commit e2fc6a2
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Showing 2 changed files with 19 additions and 17 deletions.
diff --git a/src/noise.v b/src/noise.v
@@ -1,10 +1,10 @@
 // For the SMS (1 and 2), Genesis and Game Gear, the tapped bits are bits 0 and 3 ($0009), fed back into bit 15.
 // For the SG-1000, OMV, SC-3000H, BBC Micro and Colecovision, the tapped bits are bits 0 and 1 ($0003), fed back into bit 14.
 // For the Tandy 1000, the tapped bits are bits 0 and 4 ($0011), fed back into bit 14.    
-module noise #( parameter LFSR_BITS = 15, LFSR_TAP0 = 0, LFSR_TAP1 = 1, parameter COUNTER_BITS = 10) (
+module noise #( parameter LFSR_BITS = 15, LFSR_TAP0 = 0, LFSR_TAP1 = 1, parameter COUNTER_BITS = 10 ) (
     input  wire clk,
     input  wire reset,
-    input  wire reset_lfsr,
+    input  wire restart_noise,
 
     input  wire [2:0] control,
     input  wire [COUNTER_BITS-1:0] tone_freq,
@@ -14,13 +14,8 @@ module noise #( parameter LFSR_BITS = 15, LFSR_TAP0 = 0, LFSR_TAP1 = 1, paramete
     localparam MASTER_CLOCK = 16;
     localparam TONE_DIV_2 = 2;
 
-    reg [LFSR_BITS-1:0] lfsr;
-    reg is_white_noise;
     reg [COUNTER_BITS-1:0] noise_freq;
     always @(posedge clk) begin
-        if (reset | reset_lfsr)
-            lfsr <= 1'b1 << (LFSR_BITS-1);
-
         // NF0, NF1 bits
         case(control[1:0])
             2'b00:  noise_freq <= 512 /MASTER_CLOCK/TONE_DIV_2;
@@ -39,11 +34,18 @@ module noise #( parameter LFSR_BITS = 15, LFSR_TAP0 = 0, LFSR_TAP1 = 1, paramete
         .compare(noise_freq),
         .out(noise_trigger));
 
-    always @(posedge noise_trigger) begin
-        if (is_white_noise) begin
-            lfsr <= {lfsr[LFSR_TAP0] ^ lfsr[LFSR_TAP1], lfsr[LFSR_BITS-1:1]};
+    reg is_white_noise;
+    reg [LFSR_BITS-1:0] lfsr;
+    assign reset_lfsr = reset | restart_noise;
+    always @(posedge noise_trigger, posedge reset_lfsr) begin
+        if (reset_lfsr) begin
+            lfsr <= 1'b1 << (LFSR_BITS-1);
         end else begin
-            lfsr <= {lfsr[LFSR_TAP0]                  , lfsr[LFSR_BITS-1:1]};
+            if (is_white_noise) begin
+                lfsr <= {lfsr[LFSR_TAP0] ^ lfsr[LFSR_TAP1], lfsr[LFSR_BITS-1:1]};
+            end else begin
+                lfsr <= {lfsr[LFSR_TAP0]                  , lfsr[LFSR_BITS-1:1]};
+            end
         end
     end
 

diff --git a/src/tt_um_rejunity_sn76489.v b/src/tt_um_rejunity_sn76489.v
@@ -32,7 +32,7 @@ module tt_um_rejunity_sn76489 #( parameter NUM_TONES = 3, parameter NUM_NOISES =
     reg [FREQUENCY_COUNTER_BITS-1:0]    control_tone_freq[NUM_TONES-1:0];
     reg [NOISE_CONTROL_BITS-1:0]        control_noise[NUM_NOISES-1:0];
     reg [2:0] latch_control_reg;
-    reg reset_noise;
+    reg restart_noise;
 
     always @(posedge clk) begin
         if (reset) begin
@@ -46,9 +46,9 @@ module tt_um_rejunity_sn76489 #( parameter NUM_TONES = 3, parameter NUM_NOISES =
             control_noise[0] <= 3'b100;
 
             latch_control_reg <= 0;
-            reset_noise <= 0;
+            restart_noise <= 0;
         end else begin
-            reset_noise <= 0;
+            restart_noise <= 0;
             if (data[7] == 1'b1) begin
                 case(data[6:4])
                     3'b000 : control_tone_freq[0][3:0] <= data[3:0];
@@ -57,7 +57,7 @@ module tt_um_rejunity_sn76489 #( parameter NUM_TONES = 3, parameter NUM_NOISES =
                     3'b110 : 
                         begin 
                             control_noise[0] <= data[2:0];
-                            reset_noise <= 1;
+                            restart_noise <= 1;
                         end
                     3'b001 : control_attn[0] <= data[3:0];
                     3'b011 : control_attn[1] <= data[3:0];
@@ -126,7 +126,7 @@ module tt_um_rejunity_sn76489 #( parameter NUM_TONES = 3, parameter NUM_NOISES =
             // noise #(.COUNTER_BITS(FREQUENCY_COUNTER_BITS)) gen (
             //     .clk(clk),
             //     .reset(reset),
-            //     .reset_lfsr(reset_noise),
+            //     .reset_lfsr(restart_noise),
             //     .compare(noise_freq),
             //     .is_white_noise(noise_type),
             //     .out(channels[NUM_TONES+i])
@@ -135,7 +135,7 @@ module tt_um_rejunity_sn76489 #( parameter NUM_TONES = 3, parameter NUM_NOISES =
             noise #(.COUNTER_BITS(FREQUENCY_COUNTER_BITS)) gen (
                 .clk(clk),
                 .reset(reset),
-                .reset_lfsr(reset_noise),
+                .restart_noise(restart_noise),
                 .control(control_noise[i]),
                 .tone_freq(control_tone_freq[NUM_TONES-1]), // last tone frequency
                 .out(channels[NUM_TONES+i])