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Man Pages


Manual Reference Pages  -  VASY (5)

NAME

vasy VHDL RTL subset.

[Include document man1/alc_origin.1]

CONTENTS

Description
See Also

DESCRIPTION

This document describes the VHDL subset accepted by VASY for RTL descriptions.

CONCURRENT STATEMENTS
In an RTL architecture most of the concurrent statements are supported.

Allowed concurrent statements are:

block
concurrent assertion
process
concurrent signal assignment
component instantiation statement
generate statement

SEQUENTIAL STATEMENTS
Inside a process, all sequential statements including loops, signal assignment, variable assignment are supported.

TYPE
All types usefull for synthesis are accepted (IEEE-1164 and IEEE-1076.3), and all types defined in the VHDL Alliance subset (see vbe(5) for more details).

OPERATORS
All operators usefull for synthesis are accepted, such as arithmetic, logical and relationnal operators (IEEE-1164 and IEEE-1076.3), and those defined in the VHDL Alliance subset (see vbe(5) for more details).

HARDWARE DESCRIPTION EXAMPLES

A MULTIPLEXER may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; entity mux is port( sel,a,b : in std_logic; mux_out : out std_logic ); end mux;

architecture rtl_1 of mux is begin process( sel,a,b ) begin if (sel=’1’) then mux_out <= a; else mux_out <= b; end if; end process; end rtl_1;

architecture rtl_2 of mux is begin mux_out <= a when sel=’1’ else b; end rtl_2;

A LATCH may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; entity latch is port( en,a : in std_logic; latch_out : out std_logic ); end latch;

architecture rtl_1 of latch is begin process( en, a ) begin if (en=’1’) then latch_out <= a; end if; end process; end rtl_1;

A D-FLIP-FLOP may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; entity d_ff is port( ck,a : in std_logic; d_ff_out : out std_logic ); end d_ff;

architecture rtl_1 of d_ff is begin process( ck ) begin if (ck=’1’) then d_ff_out <= a; end if; end process; end rtl_1;

architecture rtl_2 of d_ff is begin process( ck ) begin if (ck=’1’ and ck’event) then d_ff_out <= a; end if; end process; end rtl_2;

architecture rtl_3 of d_ff is begin process begin wait until ck=’1’; d_ff_out <= a; end process; end rtl_3;

A TRISTATE BUFFER may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; entity trs is port( en,a : in std_logic; trs_out : out std_logic ); end trs;

architecture rtl_1 of trs is begin process( en,a ) begin if (en=’1’) then trs_out <= a; else trs_out <= ’Z’; end if; end process; end rtl_1;

architecture rtl_2 of d_ff is begin trs_out <= a when en=’1’ else ’Z’; end rtl_2;

A RAM may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; use IEEE.numeric_std.all;

entity ram is port( clk,wr : in std_logic; adr : std_logic_vector(1 downto 0); i0 : in std_logic_vector(3 downto 0); o0 : out std_logic_vector(3 downto 0) ); end ram;

architecture rtl_1 of ram is type my_array is array (0 to 3) of std_logic_vector(3 downto 0); signal s : my_array; begin process begin wait until (clk=’0’ and clk’event); if (wr=’1’) then s(to_integer(unsigned(adr))) <= I0; end if; end process; o0 <= s(to_integer(unsigned(adr))); end rtl_1;

A ROM may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; use IEEE.numeric_std.all;

entity rom is port( adr : in std_logic_vector(1 downto 0); o0 : out std_logic_vector(3 downto 0) ); end rom;

architecture rtl_1 of rom is subtype my_word is std_logic_vector(3 downto 0); type my_array is array (0 to 3) of my_word; constant s : my_array := ( "0000", "0001", "0010", "0011" ); begin o0 <= s(to_integer(unsigned(adr))); end rtl_1;

A PRIORITY DECODER may be described as follow:

library IEEE; use IEEE.std_logic_1164.all; use IEEE.numeric_std.all;

entity decod is port( A : in std_logic_vector(3 downto 0); B : out std_logic_vector(2 downto 0)); end decod; architecture rtl_1 of decod is begin process( a ) begin b <= "111"; for i in a’range -- Static For Loop are unrolled ! loop exit when a(i)=’1’; b <= std_logic_vector(to_unsigned(i,3)); end loop; end process; end rtl_1;

SEE ALSO

vasy(1), vbe(5), vhdl(5), vst(5), boom(1), loon(1), boog(1), asimut(1), proof(1)

[Include document man1/alc_bug_report.1]

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ASIM/LIP6 VASY (5) December 11, 1999

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