diff options
Diffstat (limited to 'src/rtl/rosc_entropy_core.v')
| -rw-r--r-- | src/rtl/rosc_entropy_core.v | 57 |
1 files changed, 46 insertions, 11 deletions
diff --git a/src/rtl/rosc_entropy_core.v b/src/rtl/rosc_entropy_core.v index cd70f8a..4a43eb9 100644 --- a/src/rtl/rosc_entropy_core.v +++ b/src/rtl/rosc_entropy_core.v @@ -40,7 +40,7 @@ module rosc_entropy_core( input wire clk, input wire reset_n, - input wire en, + input wire enable, input wire [31 : 0] opa, input wire [31 : 0] opb, @@ -60,6 +60,8 @@ module rosc_entropy_core( //---------------------------------------------------------------- // Parameters. //---------------------------------------------------------------- + // 100000 cycles warmup delay. + localparam WARMUP_CYCLES = 24'h0186a0; localparam ADDER_WIDTH = 1; localparam DEBUG_DELAY = 32'h002c4b40; localparam NUM_SHIFT_BITS = 8'h20; @@ -69,6 +71,11 @@ module rosc_entropy_core( //---------------------------------------------------------------- // 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 [31 : 0] ent_shift_reg; reg [31 : 0] ent_shift_new; reg ent_shift_we; @@ -117,7 +124,7 @@ module rosc_entropy_core( assign rosc_outputs = rosc_dout; assign raw_entropy = ent_shift_reg; assign entropy_data = entropy_reg; - assign entropy_valid = entropy_valid_reg; + assign entropy_valid = entropy_valid_reg & warmup_done; assign debug = debug_reg; @@ -155,20 +162,24 @@ module rosc_entropy_core( begin if (!reset_n) begin - ent_shift_reg <= 32'h00000000; - entropy_reg <= 32'h00000000; - entropy_valid_reg <= 0; - bit_ctr_reg <= 8'h00; - sample_ctr_reg <= 8'h00; - debug_delay_ctr_reg <= 32'h00000000; - debug_reg <= 8'h00; - debug_update_reg <= 0; + ent_shift_reg <= 32'h00000000; + entropy_reg <= 32'h00000000; + entropy_valid_reg <= 0; + bit_ctr_reg <= 8'h00; + sample_ctr_reg <= 8'h00; + debug_delay_ctr_reg <= 32'h00000000; + warmup_cycle_ctr_reg <= WARMUP_CYCLES; + debug_reg <= 8'h00; + debug_update_reg <= 0; end else begin sample_ctr_reg <= sample_ctr_new; debug_update_reg <= debug_update; + if (warmup_cycle_ctr_we) + warmup_cycle_ctr_reg <= warmup_cycle_ctr_new; + if (ent_shift_we) begin ent_shift_reg <= ent_shift_new; @@ -229,6 +240,30 @@ module rosc_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_out // // Logic that implements the random output control. If we have @@ -289,7 +324,7 @@ module rosc_entropy_core( sample_ctr_new = sample_ctr_reg + 1'b1; - if (en && (sample_ctr_reg == SAMPLE_CLK_CYCLES)) + if (enable && warmup_done && (sample_ctr_reg == SAMPLE_CLK_CYCLES)) begin sample_ctr_new = 8'h00; bit_ctr_inc = 1; |