Moved the warmup counter register to the core since it is not part of the API. Added logic to implement warmup counter and disable entropy output before warmup number of cycles.

1 files changed, 53 insertions, 23 deletions

diff --git a/src/rtl/avalanche_entropy_core.v b/src/rtl/avalanche_entropy_core.v
index 582b4b6..115a94d 100644
--- a/src/rtl/avalanche_entropy_core.v
+++ b/src/rtl/avalanche_entropy_core.v
@@ -72,13 +72,20 @@ module avalanche_entropy_core(
   //----------------------------------------------------------------
   // Internal constant and parameter definitions.
   //----------------------------------------------------------------
-  parameter DEBUG_DELAY      = 32'h002c4b40;
-  parameter MIN_ENTROPY_BITS = 6'h20;
+  // 100000 cycles warmup delay.
+  localparam WARMUP_CYCLES    = 24'h0186a0;
+  localparam DEBUG_DELAY      = 32'h002c4b40;
+  localparam MIN_ENTROPY_BITS = 6'h20;
 
 
   //----------------------------------------------------------------
   // Registers including update variables and write enable.
   //----------------------------------------------------------------
+  reg [23 : 0] warmup_cycle_ctr_reg;
+  reg [23 : 0] warmup_cycle_ctr_new;
+  reg          warmup_cycle_ctr_we;
+  reg          warmup_done;
+
   reg          noise_sample0_reg;
   reg          noise_sample_reg;
 
@@ -118,19 +125,14 @@ module avalanche_entropy_core(
 
 
   //----------------------------------------------------------------
-  // Wires.
-  //----------------------------------------------------------------
-
-
-  //----------------------------------------------------------------
   // Concurrent connectivity for ports etc.
   //----------------------------------------------------------------
-  assign entropy_valid   = entropy_valid_reg;
+  assign entropy_valid   = entropy_valid_reg & warmup_done;
   assign entropy_data    = entropy_reg;
+  assign entropy_enabled = enable_reg & warmup_done;
 
   assign delta           = delta_reg;
   assign debug           = debug_reg;
-  assign entropy_enabled = enable_reg;
 
 
   //----------------------------------------------------------------
@@ -140,20 +142,21 @@ module avalanche_entropy_core(
     begin
       if (!reset_n)
         begin
-          noise_sample0_reg   <= 1'b0;
-          noise_sample_reg    <= 1'b0;
-          flank0_reg          <= 1'b0;
-          flank1_reg          <= 1'b0;
-          entropy_valid_reg     <= 1'b0;
-          entropy_reg         <= 32'h00000000;
-          entropy_bit_reg     <= 1'b0;
-          bit_ctr_reg         <= 6'h00;
-          cycle_ctr_reg       <= 32'h00000000;
-          delta_reg           <= 32'h00000000;
-          debug_delay_ctr_reg <= 32'h00000000;
-          debug_reg           <= 8'h00;
-          debug_update_reg    <= 0;
-          enable_reg          <= 0;
+          noise_sample0_reg    <= 1'b0;
+          noise_sample_reg     <= 1'b0;
+          flank0_reg           <= 1'b0;
+          flank1_reg           <= 1'b0;
+          entropy_valid_reg    <= 1'b0;
+          entropy_reg          <= 32'h00000000;
+          entropy_bit_reg      <= 1'b0;
+          bit_ctr_reg          <= 6'h00;
+          cycle_ctr_reg        <= 32'h00000000;
+          delta_reg            <= 32'h00000000;
+          debug_delay_ctr_reg  <= 32'h00000000;
+          warmup_cycle_ctr_reg <= WARMUP_CYCLES;
+          debug_reg            <= 8'h00;
+          debug_update_reg     <= 0;
+          enable_reg           <= 0;
         end
       else
         begin
@@ -171,6 +174,9 @@ module avalanche_entropy_core(
 
           enable_reg        <= enable;
 
+          if (warmup_cycle_ctr_we)
+            warmup_cycle_ctr_reg <= warmup_cycle_ctr_new;
+
           if (delta_we)
             begin
               delta_reg <= cycle_ctr_reg;
@@ -226,6 +232,30 @@ module avalanche_entropy_core(
 
 
   //----------------------------------------------------------------
+  // warmup_ctr
+  //
+  // Logic for the warmup counter. This counter starts
+  // decreasing when reset lifts and decreases until reaching zero.
+  // At zero the counter stops and asserts warmup_done.
+  //----------------------------------------------------------------
+  always @*
+    begin : warmup_ctr
+      if (warmup_cycle_ctr_reg == 0)
+        begin
+          warmup_cycle_ctr_new = 24'h000000;
+          warmup_cycle_ctr_we  = 0;
+          warmup_done          = 1;
+        end
+      else
+        begin
+          warmup_cycle_ctr_new = warmup_cycle_ctr_reg - 1'b1;
+          warmup_cycle_ctr_we  = 1;
+          warmup_done          = 0;
+        end
+    end
+
+
+  //----------------------------------------------------------------
   // entropy_collect
   //
   // We collect entropy by adding the current state of the