lm32_shifter.v

changeset 0
cd0b58aa6f83
child 26
73de224304c1
     1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/lm32_shifter.v	Sun Apr 04 20:40:03 2010 +0100
     1.3 @@ -0,0 +1,134 @@
     1.4 +// =============================================================================
     1.5 +//                           COPYRIGHT NOTICE
     1.6 +// Copyright 2006 (c) Lattice Semiconductor Corporation
     1.7 +// ALL RIGHTS RESERVED
     1.8 +// This confidential and proprietary software may be used only as authorised by
     1.9 +// a licensing agreement from Lattice Semiconductor Corporation.
    1.10 +// The entire notice above must be reproduced on all authorized copies and
    1.11 +// copies may only be made to the extent permitted by a licensing agreement from
    1.12 +// Lattice Semiconductor Corporation.
    1.13 +//
    1.14 +// Lattice Semiconductor Corporation        TEL : 1-800-Lattice (USA and Canada)
    1.15 +// 5555 NE Moore Court                            408-826-6000 (other locations)
    1.16 +// Hillsboro, OR 97124                     web  : http://www.latticesemi.com/
    1.17 +// U.S.A                                   email: techsupport@latticesemi.com
    1.18 +// =============================================================================/
    1.19 +//                         FILE DETAILS
    1.20 +// Project          : LatticeMico32
    1.21 +// File             : lm32_shifter.v
    1.22 +// Title            : Barrel shifter
    1.23 +// Dependencies     : lm32_include.v
    1.24 +// Version          : 6.1.17
    1.25 +//                  : Initial Release
    1.26 +// Version          : 7.0SP2, 3.0
    1.27 +//                  : No Change
    1.28 +// Version          : 3.1
    1.29 +//                  : No Change
    1.30 +// =============================================================================
    1.31 +
    1.32 +`include "lm32_include.v"
    1.33 +
    1.34 +/////////////////////////////////////////////////////
    1.35 +// Module interface
    1.36 +/////////////////////////////////////////////////////
    1.37 +
    1.38 +module lm32_shifter (
    1.39 +    // ----- Inputs -------
    1.40 +    clk_i,
    1.41 +    rst_i,
    1.42 +    stall_x,
    1.43 +    direction_x,
    1.44 +    sign_extend_x,
    1.45 +    operand_0_x,
    1.46 +    operand_1_x,
    1.47 +    // ----- Outputs -------
    1.48 +    shifter_result_m
    1.49 +    );
    1.50 +
    1.51 +/////////////////////////////////////////////////////
    1.52 +// Inputs
    1.53 +/////////////////////////////////////////////////////
    1.54 +
    1.55 +input clk_i;                                // Clock
    1.56 +input rst_i;                                // Reset
    1.57 +input stall_x;                              // Stall instruction in X stage
    1.58 +input direction_x;                          // Direction to shift
    1.59 +input sign_extend_x;                        // Whether shift is arithmetic (1'b1) or logical (1'b0)
    1.60 +input [`LM32_WORD_RNG] operand_0_x;         // Operand to shift
    1.61 +input [`LM32_WORD_RNG] operand_1_x;         // Operand that specifies how many bits to shift by
    1.62 +
    1.63 +/////////////////////////////////////////////////////
    1.64 +// Outputs
    1.65 +/////////////////////////////////////////////////////
    1.66 +
    1.67 +output [`LM32_WORD_RNG] shifter_result_m;   // Result of shift
    1.68 +wire   [`LM32_WORD_RNG] shifter_result_m;
    1.69 +
    1.70 +/////////////////////////////////////////////////////
    1.71 +// Internal nets and registers 
    1.72 +/////////////////////////////////////////////////////
    1.73 +
    1.74 +reg direction_m;
    1.75 +reg [`LM32_WORD_RNG] left_shift_result;
    1.76 +reg [`LM32_WORD_RNG] right_shift_result;
    1.77 +reg [`LM32_WORD_RNG] left_shift_operand;
    1.78 +wire [`LM32_WORD_RNG] right_shift_operand;
    1.79 +wire fill_value;
    1.80 +wire [`LM32_WORD_RNG] right_shift_in;
    1.81 +
    1.82 +integer shift_idx_0;
    1.83 +integer shift_idx_1;
    1.84 +
    1.85 +/////////////////////////////////////////////////////
    1.86 +// Combinational Logic
    1.87 +/////////////////////////////////////////////////////
    1.88 +    
    1.89 +// Select operands - To perform a left shift, we reverse the bits and perform a right shift
    1.90 +always @(*)
    1.91 +begin
    1.92 +    for (shift_idx_0 = 0; shift_idx_0 < `LM32_WORD_WIDTH; shift_idx_0 = shift_idx_0 + 1)
    1.93 +        left_shift_operand[`LM32_WORD_WIDTH-1-shift_idx_0] = operand_0_x[shift_idx_0];
    1.94 +end
    1.95 +assign right_shift_operand = direction_x == `LM32_SHIFT_OP_LEFT ? left_shift_operand : operand_0_x;
    1.96 +
    1.97 +// Determine fill value for right shift - Sign bit for arithmetic shift, or zero for logical shift
    1.98 +assign fill_value = (sign_extend_x == `TRUE) && (direction_x == `LM32_SHIFT_OP_RIGHT) 
    1.99 +                      ? operand_0_x[`LM32_WORD_WIDTH-1] 
   1.100 +                      : 1'b0;
   1.101 +
   1.102 +// Determine bits to shift in for right shift or rotate
   1.103 +assign right_shift_in = {`LM32_WORD_WIDTH{fill_value}};
   1.104 +
   1.105 +// Reverse bits to get left shift result
   1.106 +always @(*)
   1.107 +begin
   1.108 +    for (shift_idx_1 = 0; shift_idx_1 < `LM32_WORD_WIDTH; shift_idx_1 = shift_idx_1 + 1)
   1.109 +        left_shift_result[`LM32_WORD_WIDTH-1-shift_idx_1] = right_shift_result[shift_idx_1];
   1.110 +end
   1.111 +
   1.112 +// Select result 
   1.113 +assign shifter_result_m = direction_m == `LM32_SHIFT_OP_LEFT ? left_shift_result : right_shift_result;
   1.114 +    
   1.115 +/////////////////////////////////////////////////////
   1.116 +// Sequential Logic
   1.117 +/////////////////////////////////////////////////////
   1.118 +
   1.119 +// Perform right shift
   1.120 +always @(posedge clk_i `CFG_RESET_SENSITIVITY)
   1.121 +begin
   1.122 +    if (rst_i == `TRUE)
   1.123 +    begin
   1.124 +        right_shift_result <= {`LM32_WORD_WIDTH{1'b0}};
   1.125 +        direction_m <= `FALSE;
   1.126 +    end
   1.127 +    else
   1.128 +    begin
   1.129 +        if (stall_x == `FALSE)
   1.130 +        begin
   1.131 +            right_shift_result <= {right_shift_in, right_shift_operand} >> operand_1_x[`LM32_SHIFT_RNG];
   1.132 +            direction_m <= direction_x;
   1.133 +        end
   1.134 +    end
   1.135 +end 
   1.136 +    
   1.137 +endmodule