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-//------------------------------------------------------------------------------
-//
-// modular_adder.v
-// -----------------------------------------------------------------------------
-// Modular adder.
-//
-// 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 modular_adder
- (
- clk, rst_n,
- ena, rdy,
- ab_addr, n_addr, s_addr, s_wren,
- a_din, b_din, n_din, s_dout
- );
-
-
- //
- // 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] s_addr; // index of current S word
- output wire s_wren; // store current S 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] s_dout; // S = (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_s;
-
- /* map registers to output ports */
- assign ab_addr = index_ab;
- assign n_addr = index_n;
- assign s_addr = index_s;
-
-
- //
- // Adder
- //
- wire [31: 0] add32_s;
- wire add32_c_in;
- wire add32_c_out;
-
- adder32_wrapper adder32
- (
- .clk (clk),
- .a (a_din),
- .b (b_din),
- .s (add32_s),
- .c_in (add32_c_in),
- .c_out (add32_c_out)
- );
-
-
- //
- // Subtractor
- //
- wire [31: 0] sub32_d;
- wire sub32_b_in;
- wire sub32_b_out;
-
- subtractor32_wrapper subtractor32
- (
- .clk (clk),
- .a (add32_s),
- .b (n_din),
- .d (sub32_d),
- .b_in (sub32_b_in),
- .b_out (sub32_b_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_sum_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_sum_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_s = 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_s = fsm_shreg[FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 5) : FSM_SHREG_WIDTH - (2 * OPERAND_NUM_WORDS + 4)];
-
- wire fsm_latch_msb_carry = fsm_shreg[FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 2)];
- wire fsm_latch_msb_borrow = fsm_shreg[FSM_SHREG_WIDTH - (1 * OPERAND_NUM_WORDS + 3)];
-
- wire inc_index_ab = |fsm_shreg_inc_index_ab;
- wire inc_index_n = |fsm_shreg_inc_index_n;
- wire store_sum_ab = |fsm_shreg_store_sum_ab;
- wire store_sum_ab_n = |fsm_shreg_store_sum_ab_n;
- wire store_data_s = |fsm_shreg_store_data_s;
- wire inc_index_s = |fsm_shreg_inc_index_s;
-
- 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
-
-
-
-
-
-
-
- //
- // Carry & Borrow Masking Logic
- //
- reg add32_c_mask;
- reg sub32_b_mask;
-
- always @(posedge clk) begin
- //
- add32_c_mask <= (index_ab == WORD_INDEX_ZERO) ? 1'b1 : 1'b0;
- sub32_b_mask <= (index_n == WORD_INDEX_ZERO) ? 1'b1 : 1'b0;
- //
- end
-
- assign add32_c_in = add32_c_out & ~add32_c_mask;
- assign sub32_b_in = sub32_b_out & ~sub32_b_mask;
-
-
- //
- // Carry & Borrow Latch Logic
- //
- reg add32_carry_latch;
- reg sub32_borrow_latch;
-
- always @(posedge clk) begin
- //
- if (fsm_latch_msb_carry) add32_carry_latch <= add32_c_out;
- if (fsm_latch_msb_borrow) sub32_borrow_latch <= sub32_b_out;
- //
- end
-
-
- //
- // Intermediate Results
- //
- reg [32*OPERAND_NUM_WORDS-1:0] s_ab;
- reg [32*OPERAND_NUM_WORDS-1:0] s_ab_n;
-
- always @(posedge clk)
- //
- if (store_data_s) begin
- //
- s_ab <= {{32{1'bX}}, s_ab[32*OPERAND_NUM_WORDS-1:32]};
- s_ab_n <= {{32{1'bX}}, s_ab_n[32*OPERAND_NUM_WORDS-1:32]};
- //
- end else begin
- //
- if (store_sum_ab) s_ab <= {add32_s, s_ab[32*OPERAND_NUM_WORDS-1:32]};
- if (store_sum_ab_n) s_ab_n <= {sub32_d, s_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_s <= 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_s) index_s <= WORD_INDEX_NEXT_OR_ZERO(index_s);
- //
- end
-
-
- //
- // Output Sum Selector
- //
- wire mux_select_ab = sub32_borrow_latch && !add32_carry_latch;
-
-
- //
- // Output Data and Write Enable Logic
- //
- reg s_wren_reg;
- reg [31: 0] s_dout_reg;
- wire [31: 0] s_dout_mux = mux_select_ab ? s_ab[31:0] : s_ab_n[31:0];
-
- assign s_wren = s_wren_reg;
- assign s_dout = s_dout_reg;
-
- always @(posedge clk)
- //
- if (rdy) begin
- //
- s_wren_reg <= 1'b0;
- s_dout_reg <= {32{1'bX}};
- //
- end else begin
- //
- s_wren_reg <= store_data_s;
- s_dout_reg <= store_data_s ? s_dout_mux : {32{1'bX}};
- //
- end
-
-
-endmodule
-
-
-//------------------------------------------------------------------------------
-// End-of-File
-//------------------------------------------------------------------------------
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