Hardware Design: SIE
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| 1 | // ============================================================================= |
| 2 | // COPYRIGHT NOTICE |
| 3 | // Copyright 2006 (c) Lattice Semiconductor Corporation |
| 4 | // ALL RIGHTS RESERVED |
| 5 | // This confidential and proprietary software may be used only as authorised by |
| 6 | // a licensing agreement from Lattice Semiconductor Corporation. |
| 7 | // The entire notice above must be reproduced on all authorized copies and |
| 8 | // copies may only be made to the extent permitted by a licensing agreement from |
| 9 | // Lattice Semiconductor Corporation. |
| 10 | // |
| 11 | // Lattice Semiconductor Corporation TEL : 1-800-Lattice (USA and Canada) |
| 12 | // 5555 NE Moore Court 408-826-6000 (other locations) |
| 13 | // Hillsboro, OR 97124 web : http://www.latticesemi.com/ |
| 14 | // U.S.A email: techsupport@latticesemi.com |
| 15 | // ============================================================================/ |
| 16 | // FILE DETAILS |
| 17 | // Project : LatticeMico32 |
| 18 | // File : lm32_adder.v |
| 19 | // Title : Integer adder / subtractor with comparison flag generation |
| 20 | // Dependencies : lm32_include.v |
| 21 | // Version : 6.1.17 |
| 22 | // ============================================================================= |
| 23 | |
| 24 | `include "lm32_include.v" |
| 25 | |
| 26 | ///////////////////////////////////////////////////// |
| 27 | // Module interface |
| 28 | ///////////////////////////////////////////////////// |
| 29 | |
| 30 | module lm32_adder ( |
| 31 | // ----- Inputs ------- |
| 32 | adder_op_x, |
| 33 | adder_op_x_n, |
| 34 | operand_0_x, |
| 35 | operand_1_x, |
| 36 | // ----- Outputs ------- |
| 37 | adder_result_x, |
| 38 | adder_carry_n_x, |
| 39 | adder_overflow_x |
| 40 | ); |
| 41 | |
| 42 | ///////////////////////////////////////////////////// |
| 43 | // Inputs |
| 44 | ///////////////////////////////////////////////////// |
| 45 | |
| 46 | input adder_op_x; // Operating to perform, 0 for addition, 1 for subtraction |
| 47 | input adder_op_x_n; // Inverted version of adder_op_x |
| 48 | input [`LM32_WORD_RNG] operand_0_x; // Operand to add, or subtract from |
| 49 | input [`LM32_WORD_RNG] operand_1_x; // Opearnd to add, or subtract by |
| 50 | |
| 51 | ///////////////////////////////////////////////////// |
| 52 | // Outputs |
| 53 | ///////////////////////////////////////////////////// |
| 54 | |
| 55 | output [`LM32_WORD_RNG] adder_result_x; // Result of addition or subtraction |
| 56 | wire [`LM32_WORD_RNG] adder_result_x; |
| 57 | output adder_carry_n_x; // Inverted carry |
| 58 | wire adder_carry_n_x; |
| 59 | output adder_overflow_x; // Indicates if overflow occured, only valid for subtractions |
| 60 | reg adder_overflow_x; |
| 61 | |
| 62 | ///////////////////////////////////////////////////// |
| 63 | // Internal nets and registers |
| 64 | ///////////////////////////////////////////////////// |
| 65 | |
| 66 | wire a_sign; // Sign (i.e. positive or negative) of operand 0 |
| 67 | wire b_sign; // Sign of operand 1 |
| 68 | wire result_sign; // Sign of result |
| 69 | |
| 70 | ///////////////////////////////////////////////////// |
| 71 | // Instantiations |
| 72 | ///////////////////////////////////////////////////// |
| 73 | |
| 74 | lm32_addsub addsub ( |
| 75 | // ----- Inputs ----- |
| 76 | .DataA (operand_0_x), |
| 77 | .DataB (operand_1_x), |
| 78 | .Cin (adder_op_x), |
| 79 | .Add_Sub (adder_op_x_n), |
| 80 | // ----- Ouputs ----- |
| 81 | .Result (adder_result_x), |
| 82 | .Cout (adder_carry_n_x) |
| 83 | ); |
| 84 | |
| 85 | ///////////////////////////////////////////////////// |
| 86 | // Combinational Logic |
| 87 | ///////////////////////////////////////////////////// |
| 88 | |
| 89 | // Extract signs of operands and result |
| 90 | |
| 91 | assign a_sign = operand_0_x[`LM32_WORD_WIDTH-1]; |
| 92 | assign b_sign = operand_1_x[`LM32_WORD_WIDTH-1]; |
| 93 | assign result_sign = adder_result_x[`LM32_WORD_WIDTH-1]; |
| 94 | |
| 95 | // Determine whether an overflow occured when performing a subtraction |
| 96 | |
| 97 | always @* |
| 98 | begin |
| 99 | // +ve - -ve = -ve -> overflow |
| 100 | // -ve - +ve = +ve -> overflow |
| 101 | if ( (!a_sign & b_sign & result_sign) |
| 102 | || (a_sign & !b_sign & !result_sign) |
| 103 | ) |
| 104 | adder_overflow_x = `TRUE; |
| 105 | else |
| 106 | adder_overflow_x = `FALSE; |
| 107 | end |
| 108 | |
| 109 | endmodule |
| 110 | |
| 111 |
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