VHDL标准包与定点包详解

### VHDL标准包与定点包详解 #### 1. 标准包概述 在VHDL编程中，标准包起着至关重要的作用，它们提供了一系列的函数、类型和常量，方便开发者进行各种操作。下面我们将详细介绍一些重要的标准包及其功能。 #### 2. numeric_std_unsigned包 numeric_std_unsigned包定义了一些用于类型转换的函数和别名。以下是该包的部分代码： ```vhdl To_StdLogicVector[natural, std_ulogic_vector return std_logic_vector]; alias To_SLV is To_StdLogicVector[natural, std_ulogic_vector return std_logic_vector]; function To_StdULogicVector (arg : natural; size : natural) return std_ulogic_vector; function To_StdULogicVector (arg : natural; size_res : std_ulogic_vector) return std_ulogic_vector; alias To_Std_ULogic_Vector is To_StdULogicVector[natural, natural return std_ulogic_vector]; alias To_SULV is To_StdULogicVector[natural, natural return std_ulogic_vector]; alias To_Std_ULogic_Vector is To_StdULogicVector[natural, std_ulogic_vector return std_ulogic_vector]; alias To_SULV is To_StdULogicVector[natural, std_ulogic_vector return std_ulogic_vector]; end package numeric_std_unsigned; ``` 需要注意的是，VHDL - 87、 - 93和 - 2002版本不提供numeric_std_unsigned包。 #### 3. 标准定点包 标准定点包在处理定点数运算时非常有用。下面我们将详细介绍相关的包。 ##### 3.1 fixed_float_types包 fixed_float_types包用于定义标准定点包和标准浮点包的通用常量类型。以下是该包的代码： ```vhdl package fixed_float_types is type fixed_round_style_type is (fixed_round, fixed_truncate); type fixed_overflow_style_type is (fixed_saturate, fixed_wrap); type round_type is (round_nearest, round_inf, round_neginf, round_zero); end package fixed_float_types; ``` 该包定义了三种类型： - `fixed_round_style_type`：包含`fixed_round`（四舍五入）和`fixed_truncate`（截断）两种舍入方式。 - `fixed_overflow_style_type`：包含`fixed_saturate`（饱和）和`fixed_wrap`（回绕）两种溢出处理方式。 - `round_type`：包含`round_nearest`（四舍五入到最近值）、`round_inf`（向正无穷舍入）、`round_neginf`（向负无穷舍入）和`round_zero`（向零舍入）四种舍入类型。 ##### 3.2 fixed_generic_pkg包 fixed_generic_pkg包是一个通用的定点包，它依赖于`std.textio`、`ieee.std_logic_1164`、`ieee.numeric_std`和`ieee.fixed_float_types`包。以下是该包的部分代码： ```vhdl use std.textio.all; library ieee; use ieee.std_logic_1164.all; use ieee.numeric_std.all; use ieee.fixed_float_types.all; package fixed_generic_pkg is generic ( fixed_round_style : fixed_round_style_type := fixed_round; fixed_overflow_style : fixed_overflow_style_type := fixed_saturate; fixed_guard_bits : natural := 3; no_warning : boolean := false ); -- Author David Bishop ([email protected]) constant CopyRightNotice : string := "Copyright 2008 by IEEE. All rights reserved."; type unresolved_ufixed is array (integer range <>) of std_ulogic; type unresolved_sfixed is array (integer range <>) of std_ulogic; alias u_ufixed is unresolved_ufixed; alias u_sfixed is unresolved_sfixed; subtype ufixed is (resolved) unresolved_ufixed; subtype sfixed is (resolved) unresolved_sfix ```