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VASY(5) VHDL subset of VASY. VASY(5)

NAME

vasy VHDL RTL subset.

ORIGIN

This software belongs to the ALLIANCE CAD SYSTEM developed by the ASIM team at LIP6 laboratory of Université Pierre et Marie CURIE, in Paris, France.

Web : http://asim.lip6.fr/recherche/alliance/
E-mail : alliance-users@asim.lip6.fr

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)

BUG REPORT

This tool is under development at the ASIM department of the LIP6 laboratory.
We need your feedback to improve documentation and tools.

December 11, 1999 ASIM/LIP6