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Diffstat (limited to 'rtl/modular/modular_subtractor.v')
| -rw-r--r-- | rtl/modular/modular_subtractor.v | 292 |
1 files changed, 292 insertions, 0 deletions
diff --git a/rtl/modular/modular_subtractor.v b/rtl/modular/modular_subtractor.v new file mode 100644 index 0000000..322aec4 --- /dev/null +++ b/rtl/modular/modular_subtractor.v @@ -0,0 +1,292 @@ +//------------------------------------------------------------------------------ +// +// modular_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 modular_subtractor
+ (
+ clk, rst_n,
+ ena, rdy,
+ ab_addr, n_addr, d_addr, d_wren, + a_din, b_din, n_din, d_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] 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;
+
+ subtractor32_wrapper 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;
+
+ adder32_wrapper 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 +//------------------------------------------------------------------------------
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