found bug with calculating dt in buffer_serializer

Nexys4Game/src/hdl/SC_buffer_serializer.v

@@ -1,17 +1,19 @@
 module SC_buffer_serializer(
     input clk,
-    input song_time,
+    input [15:0] song_time,
     input [36:0] match_trigger,
     input [37*16-1:0] match_time,
 
     output reg match_en,
-    output reg [15:0] match_dt
-
+    output reg [15:0] match_dt,
+    output [15:0] queue
     );
 
     reg [17*6-1:0] match_queue; //represents a shift register with 6 shifts of 17 bits each, where the MSB means a valid match needs to be scored, and the next 16 bits are the dt
 
     initial match_queue = 0;
+
+    assign queue = match_queue[15:0];
 
     always @(posedge clk) begin
 
@@ -97,7 +99,10 @@ module SC_buffer_serializer(
         match_queue[17*5-1:0] <= match_queue[17*6-1:17]; //Shift the queue
 
         match_en <= match_queue[16]; //shift out a match
-        match_dt <= song_time - match_queue[15:0]; //SIGNED ISSUES : NEED FIXING
-
+        if(song_time >= match_queue[15:0])
+            match_dt <= song_time - match_queue[15:0];
+        else
+            match_dt <= match_queue[15:0] - song_time;
+
     end
 endmodule

Nexys4Game/src/test/SC_buffer_serializer_tb.v

@@ -11,6 +11,7 @@ module SC_buffer_serializer_tb;
     // Outputs
     wire match_en;
     wire [15:0] match_dt;
+    wire [15:0] queue;
 
     // Instantiate the Unit Under Test (UUT)
     SC_buffer_serializer uut (
@@ -19,11 +20,12 @@ module SC_buffer_serializer_tb;
         .match_trigger(match_trigger),
         .match_time(match_time),
         .match_en(match_en),
-        .match_dt(match_dt)
+        .match_dt(match_dt),
+        .queue(queue)
     );
 
     always #5 clk = !clk;
-    always #10 song_time = song_time + 1;
+    always #100 song_time = song_time + 1;
     initial begin
         // Initialize Inputs
         clk = 0;
@@ -34,7 +36,7 @@ module SC_buffer_serializer_tb;
         #100;
 
         //Stimulus
-
+        #1000
         match_trigger = 1; //match e2
         match_time[15:0] = 7;
         #10