Combinational implementation of EdgeDetector with zero latency

Author: pConst

ClkDivider.v renamed to 00_obsolete/ClkDivider.v

@@ -0,0 +1,57 @@
+//------------------------------------------------------------------------------
+// EdgeDetect.sv
+// Konstantin Pavlov, [email protected]
+//------------------------------------------------------------------------------
+
+// INFO ------------------------------------------------------------------------
+// Variable width edge detector
+// Features one tick propagation time
+
+
+/* --- INSTANTIATION TEMPLATE BEGIN ---
+
+EdgeDetect #(
+  .WIDTH( 32 )
+) ED1 (
+  .clk( clk ),
+  .nrst( 1'b1 ),
+  .in(  ),
+  .rising(  ),
+  .falling(  ),
+  .both(  )
+);
+
+--- INSTANTIATION TEMPLATE END ---*/
+
+
+module EdgeDetect #(
+  WIDTH = 1
+)(
+  input clk,
+  input nrst,
+
+  input [(WIDTH-1):0] in,
+  output logic [(WIDTH-1):0] rising = 0,
+  output logic [(WIDTH-1):0] falling = 0,
+  output [(WIDTH-1):0] both
+);
+
+
+logic [(WIDTH-1):0] in_prev = 0;
+
+always_ff @(posedge clk) begin
+  if ( ~nrst ) begin
+    in_prev <= 0;
+    rising <= 0;
+    falling <= 0;
+  end
+  else begin
+    in_prev <= in;
+    rising[(WIDTH-1):0] <= in[(WIDTH-1):0] & ~in_prev[(WIDTH-1):0];
+    falling[(WIDTH-1):0] <= ~in[(WIDTH-1):0] & in_prev[(WIDTH-1):0];
+  end
+end
+
+assign both[(WIDTH-1):0] = rising[(WIDTH-1):0] | falling[(WIDTH-1):0];
+
+endmodule

00_obsolete/EdgeDetect.sv

@@ -4,54 +4,51 @@
 //------------------------------------------------------------------------------
 
 // INFO ------------------------------------------------------------------------
-// Variable width edge detector
-// Features one tick propagation time
+// Edge detector, ver.2
+// Combinational implementation (zero ticks delay)
+//
+// In case when "in" port has toggle rate 100% (changes every clock period)
+//    "rising" and "falling" outputs will completely replicate input
+//    "both" output will be always active in this case
 
 
 /* --- INSTANTIATION TEMPLATE BEGIN ---
 
-EdgeDetect #(
-  .WIDTH( 32 )
-) ED1 (
-  .clk( clk ),
-  .nrst( 1'b1 ),
-  .in(  ),
-  .rising(  ),
+EdgeDetect ED1[31:0] (
+  .clk( {32{clk}} ),
+  .nrst( {32{1'b1}} ),
+  .in( in[31:0] ),
+  .rising( out[31:0] ),
   .falling(  ),
   .both(  )
 );
 
 --- INSTANTIATION TEMPLATE END ---*/
 
 
-module EdgeDetect #(
-  WIDTH = 1
-)(
+module EdgeDetect(
   input clk,
   input nrst,
 
-  input [(WIDTH-1):0] in,
-  output logic [(WIDTH-1):0] rising = 0,
-  output logic [(WIDTH-1):0] falling = 0,
-  output [(WIDTH-1):0] both
+  input in,
+  output logic rising,
+  output logic falling,
+  output logic both
 );
 
-
-logic [(WIDTH-1):0] in_prev = 0;
-
+logic in_d = 0;
 always_ff @(posedge clk) begin
   if ( ~nrst ) begin
-    in_prev <= 0;
-    rising <= 0;
-    falling <= 0;
-  end
-  else begin
-    in_prev <= in;
-    rising[(WIDTH-1):0] <= in[(WIDTH-1):0] & ~in_prev[(WIDTH-1):0];
-    falling[(WIDTH-1):0] <= ~in[(WIDTH-1):0] & in_prev[(WIDTH-1):0];
+    in_d <= 0;
+  end else begin
+    in_d <= in;
   end
 end
 
-assign both[(WIDTH-1):0] = rising[(WIDTH-1):0] | falling[(WIDTH-1):0];
+always_comb begin
+  rising = nrst && (in && ~in_d);
+  falling = nrst && (~in && in_d);
+  both = nrst && (rising || falling);
+end
 
 endmodule

EdgeDetect.v renamed to 00_obsolete/EdgeDetect.v

@@ -0,0 +1,84 @@
+//------------------------------------------------------------------------------
+// EdgeDetect_tb.sv
+// Konstantin Pavlov, [email protected]
+//------------------------------------------------------------------------------
+
+// INFO ------------------------------------------------------------------------
+//
+
+`timescale 1ns / 1ps
+
+module EdgeDetect_tb();
+
+logic clk200;
+initial begin
+  #0 clk200 = 1;
+  forever
+    #2.5 clk200 = ~clk200;
+end
+
+logic rst;
+initial begin
+  #10.2 rst = 1;
+  #5 rst = 0;
+  //#10000;
+  forever begin
+    #9985 rst = ~rst;
+    #5 rst = ~rst;
+  end
+end
+
+logic nrst;
+assign nrst = ~rst;
+
+logic rst_once;
+initial begin       // initializing non-X data before PLL starts
+  #10.2 rst_once = 1;
+  #5 rst_once = 0;
+end
+initial begin
+  #510.2 rst_once = 1;    // PLL starts at 500ns, clock appears, so doing the reset for modules
+  #5 rst_once = 0;
+end
+
+logic nrst_once;
+assign nrst_once = ~rst_once;
+
+logic [31:0] DerivedClocks;
+ClkDivider #(
+  .WIDTH( 32 )
+) CD1 (
+  .clk( clk200 ),
+  .nrst( nrst_once ),
+  .out( DerivedClocks[31:0] )
+);
+
+logic [15:0] RandomNumber1;
+c_rand RNG1 (
+  .clk( clk200 ),
+  .rst( rst_once ),
+  .reseed( 1'b0 ),
+  .seed_val( DerivedClocks[31:0] ),
+  .out( RandomNumber1[15:0] )
+);
+
+logic start;
+initial begin
+  #0 start = 1'b0;
+  #100.2 start = 1'b1;
+  #5 start = 1'b0;
+end
+
+// Module under test ==========================================================
+
+EdgeDetect ED1[15:0] (
+  .clk( {16{clk200}} ),
+  .nrst( {16{nrst_once}} ),
+  .in( RandomNumber1[15:0] ),
+  .rising(  ),
+  .falling(  ),
+  .both(  )
+);
+
+
+endmodule

EdgeDetect.sv

@@ -15,7 +15,7 @@ reg clk200;
 initial begin
   #0 clk200 = 1;
   forever
-
+    #2.5 clk200 = ~clk200;
 end
 
 reg rst;