bat/tests/syntax-tests/highlighted/Verilog/div_pipelined.v

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2021-05-30 10:49:43 +02:00
// Copyright 2018 Schuyler Eldridge
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Implements a fixed-point parameterized pipelined division
// operation. Outputs are expected to be on range [-1,1), techincally
// [-1,2^(BITS-1)-1/2^(BITS-1)]. There is no convergent rounding.
//
// [TODO] Implement optional convergent rounding and some form of
// variable output binary point placement. There are arguments in
// these changes that make sense (specifically, adding an additional
// bit results in a gain of one value when all the other 2^6 values
// greater than 1 aren't used). Other improvements that are needed: 1)
// quotient_gen is getting smaller by one bit in every stage, it would
// make more sense to generate this as such, 2) there's some weird
// initial behavior after rst_n is deasserted, you get weird output on
// the quotient line for a number of cycles.
//
// [TODO] This doesn't exactly behave as expected if you specify
// different BITS and STAGES parameters (which for a functional
// module, should be implemented). Note, that this technically works,
// but needs more investigation to fully understand its properties.
`timescale 1ns / 1ps
module div_pipelined
 (
 input clk,
 input rst_n,
 input start,
 input [BITS-1:0] dividend,
 input [BITS-1:0] divisor,
 output reg data_valid,
 output reg div_by_zero,
 output reg [STAGES-1:0] quotient
 // output reg [7:0] quotient_correct
 );
 // WARNING!!! THESE PARAMETERS ARE INTENDED TO BE MODIFIED IN A TOP
 // LEVEL MODULE. LOCAL CHANGES HERE WILL, MOST LIKELY, BE
 // OVERWRITTEN!
 parameter
 BITS = 8,
 STAGES = BITS;
 // y = a/bQ
 reg [STAGES-1:0] start_gen, negative_quotient_gen, div_by_zero_gen;
 reg [BITS*2*(STAGES-1)-1:0] dividend_gen, divisor_gen, quotient_gen;
 wire [BITS-1:0] pad_dividend;
 wire [BITS-2:0] pad_divisor;
 assign pad_dividend = 0;
 assign pad_divisor = 0;
 // sign conversion stage
 always @ (posedge clk or negedge rst_n)
 begin
 if (!rst_n) begin
 div_by_zero_gen[0] <= 0;
 start_gen[0] <=0;
 negative_quotient_gen[0] <= 0;
 dividend_gen[BITS*2-1:0] <= 0;
 divisor_gen[BITS*2-1:0] <= 0; end
 else begin
 div_by_zero_gen[0] <= (divisor == 0);
 start_gen[0] <= start;
 negative_quotient_gen[0] <= dividend[BITS-1] ^ divisor[BITS-1];
 dividend_gen[BITS*2-1:0] <= (dividend[BITS-1]) ? ~{dividend,pad_dividend} + 1 : {dividend,pad_dividend};
 divisor_gen[BITS*2-1:0] <= (divisor [BITS-1]) ? ~{1'b1,divisor, pad_divisor} + 1 : {1'b0,divisor, pad_divisor};
 end
 end
 // first computation stage
 always @ (posedge clk or negedge rst_n) begin
 if (!rst_n) begin
 div_by_zero_gen[1] <= 0;
 start_gen[1] <= 0;
 negative_quotient_gen[1] <= 0;
 divisor_gen[BITS*2*2-1:BITS*2] <= 0;
 quotient_gen[BITS*2-1:0] <= 0;
 dividend_gen[BITS*2*2-1:BITS*2] <= 0;
 end
 else begin
 div_by_zero_gen[1] <= div_by_zero_gen[0];
 start_gen[1] <= start_gen[0];
 negative_quotient_gen[1] <= negative_quotient_gen[0];
 divisor_gen[BITS*2*2-1:BITS*2] <= divisor_gen[BITS*2-1:0] >> 1;
 if ( dividend_gen[BITS*2-1:0] >= divisor_gen[BITS*2-1:0]) begin
 quotient_gen[BITS*2-1:0] <= 1 << STAGES - 2;
 dividend_gen[BITS*2*2-1:BITS*2] <= dividend_gen[BITS*2-1:0] - divisor_gen[BITS*2-1:0];
 end
 else begin
 quotient_gen[BITS*2-1:0] <= 0;
 dividend_gen[BITS*2*2-1:BITS*2] <= dividend_gen[BITS*2-1:0];
 end
 end // else: !if(!rst_n)
 end // always @ (posedge clk)
 generate
 genvar i;
 for (i = 1; i < STAGES - 2; i = i + 1) begin : pipeline
 always @ (posedge clk or negedge rst_n) begin
 if (!rst_n) begin
 div_by_zero_gen[i+1] <= 0;
 start_gen[i+1] <= 0;
 negative_quotient_gen[i+1] <= 0;
 divisor_gen[BITS*2*(i+2)-1:BITS*2*(i+1)] <= 0;
 quotient_gen[BITS*2*(i+1)-1:BITS*2*i] <= 0;
 dividend_gen[BITS*2*(i+2)-1:BITS*2*(i+1)] <= 0;
 end
 else begin
 div_by_zero_gen[i+1] <= div_by_zero_gen[i];
 start_gen[i+1] <= start_gen[i];
 negative_quotient_gen[i+1] <= negative_quotient_gen[i];
 divisor_gen[BITS*2*(i+2)-1:BITS*2*(i+1)] <= divisor_gen[BITS*2*(i+1)-1:BITS*2*i] >> 1;
 if (dividend_gen[BITS*2*(i+1)-1:BITS*2*i] >= divisor_gen[BITS*2*(i+1)-1:BITS*2*i]) begin
 quotient_gen[BITS*2*(i+1)-1:BITS*2*i] <= quotient_gen[BITS*2*i-1:BITS*2*(i-1)] | (1 << (STAGES-2-i));
 dividend_gen[BITS*2*(i+2)-1:BITS*2*(i+1)] <= dividend_gen[BITS*2*(i+1)-1:BITS*2*i] - divisor_gen[BITS*2*(i+1)-1:BITS*2*i];
 end
 else begin
 quotient_gen[BITS*2*(i+1)-1:BITS*2*i] <= quotient_gen[BITS*2*i-1:BITS*2*(i-1)];
 dividend_gen[BITS*2*(i+2)-1:BITS*2*(i+1)] <= dividend_gen[BITS*2*(i+1)-1:BITS*2*i];
 end
 end // else: !if(!rst_n)
 end // always @ (posedge clk or negedge rst_n)
 end // block: pipeline
 endgenerate
 // last computation stage
 always @ (posedge clk or negedge rst_n) begin
 if (!rst_n) begin
 div_by_zero_gen[STAGES-1] <= 0;
 start_gen[STAGES-1] <= 0;
 negative_quotient_gen[STAGES-1] <= 0;
 quotient_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)] <= 0;
 end
 else begin
 div_by_zero_gen[STAGES-1] <= div_by_zero_gen[STAGES-2];
 start_gen[STAGES-1] <= start_gen[STAGES-2];
 negative_quotient_gen[STAGES-1] <= negative_quotient_gen[STAGES-2];
 if ( dividend_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)] >= divisor_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)] )
 quotient_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)] <= quotient_gen[BITS*2*(STAGES-2)-1:BITS*2*(STAGES-3)] | 1;
 else
 quotient_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)] <= quotient_gen[BITS*2*(STAGES-2)-1:BITS*2*(STAGES-3)];
 end // else: !if(!rst_n)
 end // always @ (posedge clk)
 // sign conversion stage
 always @ (posedge clk or negedge rst_n) begin
 if (!rst_n) begin
 div_by_zero <= 0;
 data_valid <= 0;
 quotient <= 0;
 end
 else begin
 div_by_zero <= div_by_zero_gen[STAGES-1];
 data_valid <= start_gen[STAGES-1];
 quotient <= (negative_quotient_gen[STAGES-1]) ? ~quotient_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)] + 1 : quotient_gen[BITS*2*(STAGES-1)-1:BITS*2*(STAGES-2)];
 end
 end
endmodule