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//======================================================================
//
// fpga_entropy.v
// --------------
// Top level wrapper for the fpga entropy generator core.
//
//
// Author: Joachim Strombergson
// Copyright (c) 2014, Secworks Sweden AB
//
// Redistribution and use in source and binary forms, with or
// without modification, are permitted provided that the following
// conditions are met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in
// the documentation and/or other materials provided with the
// distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//======================================================================
module fpga_entropy(
input wire clk,
input wire reset_n,
// API interface.
input wire cs,
input wire we,
input wire [7 : 0] address,
input wire [31 : 0] write_data,
output wire [31 : 0] read_data,
output wire error,
// Debug output.
output wire [7 : 0] debug
);
//----------------------------------------------------------------
// Internal constant and parameter definitions.
//----------------------------------------------------------------
// API addresses.
parameter ADDR_CORE_NAME0 = 8'h00;
parameter ADDR_CORE_NAME1 = 8'h01;
parameter ADDR_CORE_VERSION = 8'h02;
parameter ADDR_UPDATE = 8'h10;
parameter ADDR_OPA = 8'h11;
parameter ADDR_RND_READ = 8'h20;
// Core ID constants.
parameter CORE_NAME0 = 32'h66706761; // "fpga"
parameter CORE_NAME1 = 32'h5f656e74; // "_ent"
parameter CORE_VERSION = 32'h302e3031; // "0.01"
// Default value assigned to operand A.
// Operand B will be the inverse value of operand A.
parameter DEFAULT_OPA = 32'haaaaaaaa;
// Delay in cycles between updating the debug port with
// a new random value sampled from the rng core port.
// Corresponds to about 1/20s with a clock @ 50 MHz.
parameter DELAY_MAX = 32'h002625a0;
//----------------------------------------------------------------
// Registers including update variables and write enable.
//----------------------------------------------------------------
reg [31 : 0] opa_reg;
reg [31 : 0] opb_reg;
reg [31 : 0] opa_new;
reg opa_we;
reg update_reg;
reg update_new;
reg update_we;
reg [31 : 0] delay_ctr_reg;
reg [31 : 0] delay_ctr_new;
reg [7 : 0] debug_reg;
reg debug_we;
//----------------------------------------------------------------
// Wires.
//----------------------------------------------------------------
reg tmp_error;
reg [31 : 0] tmp_read_data;
wire [31 : 0] core_rnd;
//----------------------------------------------------------------
// Concurrent connectivity for ports etc.
//----------------------------------------------------------------
assign read_data = tmp_read_data;
assign error = tmp_error;
assign debug = debug_reg;
//----------------------------------------------------------------
// core
//
// Instantiation of the uart core.
//----------------------------------------------------------------
fpga_entropy_core core(
.clk(clk),
.reset_n(reset_n),
.opa(opa_reg),
.opb(opb_reg),
.update(update_reg),
.rnd(core_rnd)
);
//----------------------------------------------------------------
// reg_update
//
// Update functionality for all registers in the core.
// All registers are positive edge triggered with synchronous
// active low reset. All registers have write enable.
//----------------------------------------------------------------
always @ (posedge clk)
begin: reg_update
if (!reset_n)
begin
opa_reg <= DEFAULT_OPA;
opb_reg <= ~DEFAULT_OPA;
update_reg <= 1;
debug_reg <= 8'h00;
end
else
begin
delay_ctr_reg <= delay_ctr_new;
if (opa_we)
begin
opa_reg <= opa_new;
opb_reg <= ~opa_new;
end
if (update_we)
begin
update_reg <= update_new;
end
if (debug_we)
begin
debug_reg <= core_rnd[7 : 0];
end
end
end // reg_update
//----------------------------------------------------------------
// delay_ctr
//
// Simple counter that counts to DELAY_MAC. Used to slow down
// the debug port updates to human speeds.
//----------------------------------------------------------------
always @*
begin : delay_ctr
debug_we = 0;
if (delay_ctr_reg == DELAY_MAX)
begin
delay_ctr_new = 32'h00000000;
debug_we = 1;
end
else
begin
delay_ctr_new = delay_ctr_reg + 1'b1;
end
end // delay_ctr
//----------------------------------------------------------------
// api
//
// The core API that allows an internal host to control the
// core functionality.
//----------------------------------------------------------------
always @*
begin: api
// Default assignments.
opa_new = 32'h00000000;
opa_we = 0;
update_new = 0;
update_we = 0;
tmp_read_data = 32'h00000000;
tmp_error = 0;
if (cs)
begin
if (we)
begin
// Write operations.
case (address)
ADDR_UPDATE:
begin
update_new = write_data[0];
update_we = 1;
end
ADDR_OPA:
begin
opa_new = write_data;
opa_we = 1;
end
default:
begin
tmp_error = 1;
end
endcase // case (address)
end
else
begin
// Read operations.
case (address)
ADDR_CORE_NAME0:
begin
tmp_read_data = CORE_NAME0;
end
ADDR_CORE_NAME1:
begin
tmp_read_data = CORE_NAME1;
end
ADDR_CORE_VERSION:
begin
tmp_read_data = CORE_VERSION;
end
ADDR_UPDATE:
begin
tmp_read_data = update_reg;
end
ADDR_OPA:
begin
tmp_read_data = opa_reg;
end
ADDR_RND_READ:
begin
tmp_read_data = core_rnd;
end
default:
begin
tmp_error = 1;
end
endcase // case (address)
end
end
end
endmodule // fpga_entropy
//======================================================================
// EOF fpga_entropy.v
//======================================================================
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