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diff --git a/mod_subtractor.v b/mod_subtractor.v new file mode 100644 index 0000000..9b4b7e9 --- /dev/null +++ b/mod_subtractor.v @@ -0,0 +1,298 @@ +//------------------------------------------------------------------------------ +// +// mod_subtractor.v +// ----------------------------------------------------------------------------- +// Modular subtractor. +// +// Authors: Pavel Shatov +// +// Copyright (c) 2016, NORDUnet A/S +// +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are met: +// +// - Redistributions of source code must retain the above copyright notice, +// this list of conditions and the following disclaimer. +// +// - 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. +// +// - Neither the name of the NORDUnet nor the names of its contributors may be +// used to endorse or promote products derived from this software without +// specific prior written permission. +// +// 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 HOLDER 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 mod_subtractor + ( + clk, rst_n, + ena, rdy, + ab_addr, n_addr, d_addr, d_wren, + a_din, b_din, n_din, d_dout + ); + + + // + // Settings + // + `include "ed25519_settings.vh" + + + // + // Parameters + // + parameter OPERAND_NUM_WORDS = 8; + parameter WORD_COUNTER_WIDTH = 3; + + + // + // Handy Numbers + // + localparam [WORD_COUNTER_WIDTH-1:0] WORD_INDEX_ZERO = 0; + localparam [WORD_COUNTER_WIDTH-1:0] WORD_INDEX_LAST = OPERAND_NUM_WORDS - 1; + + + // + // Handy Functions + // + function [WORD_COUNTER_WIDTH-1:0] WORD_INDEX_NEXT_OR_ZERO; + input [WORD_COUNTER_WIDTH-1:0] WORD_INDEX_CURRENT; + begin + WORD_INDEX_NEXT_OR_ZERO = (WORD_INDEX_CURRENT < WORD_INDEX_LAST) ? + WORD_INDEX_CURRENT + 1'b1 : WORD_INDEX_ZERO; + end + endfunction + + + // + // Ports + // + input wire clk; // system clock + input wire rst_n; // active-low async reset + + input wire ena; // enable input + output wire rdy; // ready output + + output wire [WORD_COUNTER_WIDTH-1:0] ab_addr; // index of current A and B words + output wire [WORD_COUNTER_WIDTH-1:0] n_addr; // index of current N word + output wire [WORD_COUNTER_WIDTH-1:0] d_addr; // index of current D word + output wire d_wren; // store current D word now + + input wire [ 31:0] a_din; // A + input wire [ 31:0] b_din; // B + input wire [ 31:0] n_din; // N + output wire [ 31:0] d_dout; // D = (A - B) mod N + + + // + // Word Indices + // + reg [WORD_COUNTER_WIDTH-1:0] index_ab; + reg [WORD_COUNTER_WIDTH-1:0] index_n; + reg [WORD_COUNTER_WIDTH-1:0] index_d; + + /* map registers to output ports */ + assign ab_addr = index_ab; + assign n_addr = index_n; + assign d_addr = index_d; + + + // + // Subtractor + // + wire [31: 0] sub32_d; + wire sub32_b_in; + wire sub32_b_out; + + `ED25519_SUB32_PRIMITIVE subtractor32 + ( + .clk (clk), + .a (a_din), + .b (b_din), + .d (sub32_d), + .b_in (sub32_b_in), + .b_out (sub32_b_out) + ); + + + // + // Adder + // + wire [31: 0] add32_s; + wire add32_c_in; + wire add32_c_out; + + `ED25519_ADD32_PRIMITIVE adder32 + ( + .clk (clk), + .a (sub32_d), + .b (n_din), + .s (add32_s), + .c_in (add32_c_in), + .c_out (add32_c_out) + ); + + + // + // FSM + // + + localparam FSM_SHREG_WIDTH = 2*OPERAND_NUM_WORDS + 5; + + reg [FSM_SHREG_WIDTH-1:0] fsm_shreg; + + assign rdy = fsm_shreg[0]; + + wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_inc_index_ab = fsm_shreg[FSM_SHREG_WIDTH - (0 * OPERAND_NUM_WORDS + 1) : FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 0)]; + wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_inc_index_n = fsm_shreg[FSM_SHREG_WIDTH - (0 * OPERAND_NUM_WORDS + 2) : FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 1)]; + wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_store_dif_ab = fsm_shreg[FSM_SHREG_WIDTH - (0 * OPERAND_NUM_WORDS + 3) : FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 2)]; + wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_store_dif_ab_n = fsm_shreg[FSM_SHREG_WIDTH - (0 * OPERAND_NUM_WORDS + 4) : FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 3)]; + wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_store_data_d = fsm_shreg[FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 4) : FSM_SHREG_WIDTH - (2 * OPERAND_NUM_WORDS + 3)]; + wire [OPERAND_NUM_WORDS-1:0] fsm_shreg_inc_index_d = fsm_shreg[FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 5) : FSM_SHREG_WIDTH - (2 * OPERAND_NUM_WORDS + 4)]; + + wire fsm_latch_msb_borrow = fsm_shreg[FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 2)]; + + wire inc_index_ab = |fsm_shreg_inc_index_ab; + wire inc_index_n = |fsm_shreg_inc_index_n; + wire store_dif_ab = |fsm_shreg_store_dif_ab; + wire store_dif_ab_n = |fsm_shreg_store_dif_ab_n; + wire store_data_d = |fsm_shreg_store_data_d; + wire inc_index_d = |fsm_shreg_inc_index_d; + + always @(posedge clk or negedge rst_n) + // + if (rst_n == 1'b0) + // + fsm_shreg <= {{FSM_SHREG_WIDTH-1{1'b0}}, 1'b1}; + // + else begin + // + if (rdy) fsm_shreg <= {ena, {FSM_SHREG_WIDTH-2{1'b0}}, ~ena}; + // + else fsm_shreg <= {1'b0, fsm_shreg[FSM_SHREG_WIDTH-1:1]}; + // + end + + + // + // Borrow & Carry Masking Logic + // + reg sub32_b_mask; + reg add32_c_mask; + + + always @(posedge clk) begin + // + sub32_b_mask <= (index_ab == WORD_INDEX_ZERO) ? 1'b1 : 1'b0; + add32_c_mask <= (index_n == WORD_INDEX_ZERO) ? 1'b1 : 1'b0; + // + end + + assign sub32_b_in = sub32_b_out & ~sub32_b_mask; + assign add32_c_in = add32_c_out & ~add32_c_mask; + + + + // + // Borrow & Carry Latch Logic + // + reg sub32_borrow_latch; + + always @(posedge clk) begin + // + if (fsm_latch_msb_borrow) sub32_borrow_latch <= sub32_b_out; + // + end + + + // + // Intermediate Results + // + reg [32*OPERAND_NUM_WORDS-1:0] d_ab; + reg [32*OPERAND_NUM_WORDS-1:0] d_ab_n; + + always @(posedge clk) + // + if (store_data_d) begin + // + d_ab <= {{32{1'bX}}, d_ab[32*OPERAND_NUM_WORDS-1:32]}; + d_ab_n <= {{32{1'bX}}, d_ab_n[32*OPERAND_NUM_WORDS-1:32]}; + // + end else begin + // + if (store_dif_ab) d_ab <= {sub32_d, d_ab[32*OPERAND_NUM_WORDS-1:32]}; + if (store_dif_ab_n) d_ab_n <= {add32_s, d_ab_n[32*OPERAND_NUM_WORDS-1:32]}; + // + end + + + // + // Word Index Increment Logic + // + always @(posedge clk) + // + if (rdy) begin + // + index_ab <= WORD_INDEX_ZERO; + index_n <= WORD_INDEX_ZERO; + index_d <= WORD_INDEX_ZERO; + // + end else begin + // + if (inc_index_ab) index_ab <= WORD_INDEX_NEXT_OR_ZERO(index_ab); + if (inc_index_n) index_n <= WORD_INDEX_NEXT_OR_ZERO(index_n); + if (inc_index_d) index_d <= WORD_INDEX_NEXT_OR_ZERO(index_d); + // + end + + + // + // Output Sum Selector + // + wire mux_select_ab_n = sub32_borrow_latch; + + + // + // Output Data and Write Enable Logic + // + reg d_wren_reg; + reg [31: 0] d_dout_reg; + wire [31: 0] d_dout_mux = mux_select_ab_n ? d_ab_n[31:0] : d_ab[31:0]; + + assign d_wren = d_wren_reg; + assign d_dout = d_dout_reg; + + always @(posedge clk) + // + if (rdy) begin + // + d_wren_reg <= 1'b0; + d_dout_reg <= {32{1'bX}}; + // + end else begin + // + d_wren_reg <= store_data_d; + d_dout_reg <= store_data_d ? d_dout_mux : {32{1'bX}}; + // + end + + +endmodule + + +//------------------------------------------------------------------------------ +// End-of-File +//------------------------------------------------------------------------------ |