AR# 4508

Description

General Description:

How do I selectively disable IBUF/OBUF insertion?

Synplify will automatically insert an IBUF/OBUF on all signals listed in the port list of the top-level module/entity of the design. If a pre-optimized netlist that contains I/O cells (such as IBUF, OBUF, OFD, etc.) is included, these ports must be marked to disable this feature.

Define the module/entity that contains embedded I/O cells as a black_box. Then, for these ports, attach an attribute called ".ispad" (5.0.6 or earlier) or "black_box_pad_pin" (5.0.7 and later), which declares the ports as pads. This will prevent Synplify from inserting buffers for them.

In Synplify 5.0.7 and later, the "black_box_pad_pin" attribute is introduced. This is recognized for all Xilinx families. However, the ".ispad" attribute is recognized for all Xilinx families except Virtex.

NOTE: The ".ispad" and "black_box_pad_pin" are directives and can be applied only in HDL; they cannot be applied through the SDC file.

Solution

Verilog (selective I/O insertion), using the ".ispad" attribute

NOTE:

- This method is used with Synplify 5.0.6 and earlier.

- The ".ispad" attribute is recognized for all families except Virtex.

module FOO1 (A, B, C, WE);

input [3:0] A, B;

output [3:0] C;

output WE;

assign C = A + B;

assign WE = A[0] & A[1] & A[2] & A[3];

endmodule

// The ".ispad" is applied to the ports of the module that

// are declared as a black_box.

module FOO2 (A, B, WE, D, ACT) /* synthesis syn_black_box */;

input [3:0] A, B;

input WE;

output [3:0] D /* synthesis .ispad = 1 */;

output ACT /* synthesis .ispad = 1 */;

endmodule

module TOP (A, B1, B2, C, D, ACTIVE);

input [3:0] A, B1, B2;

output [3:0] C, D;

output ACTIVE;

wire WE;

FOO1 U0 (.A (A), .B (B1), .C (C), .WE (WE));

FOO2 U1 (.A (A), .B (B2), .WE (WE), .D (D), .ACT (ACTIVE));

endmodule

VHDL (selective I/O insertion), using the ".ispad" attribute

NOTE:

- This method is used with Synplify 5.0.6 and earlier.

- The ".ispad" attribute is recognized for all families except Virtex.

- Define a black box entity and architecture for the model.

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

entity FOO1 is

port(A, B : in std_logic_vector(3 downto 0);

C : out std_logic_vector(3 downto 0);

WE : out std_logic);

end FOO1;

architecture BEHAVE of FOO1 is

begin

C <= A + B;

WE <= A(0) and A(1) and A(2) and A(3);

end BEHAVE;

library ieee;

use ieee.std_logic_1164.all;

entity FOO2 is

port(A, B : in std_logic_vector(3 downto 0);

WE : in std_logic;

D : out std_logic_vector(3 downto 0);

ACT : out std_logic);

-- The .ispad attribute is applied to the ports of the entity

-- that is declared as a black box.

attribute \.ispad\ : boolean;

attribute \.ispad\ of D : signal is true;

attribute \.ispad\ of ACT : signal is true;

end FOO2;

architecture BEHAVE of foo2 is

attribute syn_black_box : boolean;

attribute syn_black_box of BEHAVE : architecture is true;

begin

end BEHAVE;

library ieee;

use ieee.std_logic_1164.all;

entity TOP is

port (A, B1, B2 : in std_logic_vector(3 downto 0);

C, D : out std_logic_vector(3 downto 0);

ACTIVE : out std_logic);

end TOP;

architecture BEAVE of top is

component FOO1

port(A, B : in std_logic_vector(3 downto 0);

C : out std_logic_vector(3 downto 0);

WE : out std_logic);

end component;

component FOO2

port(A, B : in std_logic_vector(3 downto 0);

WE : in std_logic;

D : out std_logic_vector(3 downto 0);

ACT : out std_logic);

end component;

signal WE : std_logic;

begin

U0 : FOO1 port map (A => A, B => B1, C => C, WE => WE);

U1 : FOO2 port map (A => A, B => B2, WE => WE, D => D, ACT => ACTIVE);

end BEAVE;

VHDL (selective I/O insertion), using the "black_box_pad_pin" attribute

NOTE:

- This method is used with Synplify 5.0.7 and later.

- The "black_box_pad_pin" attribute is recognized for all families.

- Define a black box component. It is not necessary to instantiate a black box entity and architecture.

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

entity FOO1 is

port(A, B : in std_logic_vector(3 downto 0);

C : out std_logic_vector(3 downto 0);

WE : out std_logic);

end FOO1;

architecture BEHAVE of FOO1 is

begin

C <= A + B;

WE <= A(0) and A(1) and A(2) and A(3);

end BEHAVE;

library ieee, synplify;

use ieee.std_logic_1164.all;

use synplify.attributes.all; -- Define Synplify attributes

entity TOP is

port (A, B1, B2 : in std_logic_vector(3 downto 0);

C, D : out std_logic_vector(3 downto 0);

ACTIVE : out std_logic);

end TOP;

architecture BEAVE of top is

component FOO1

port(A, B : in std_logic_vector(3 downto 0);

C : out std_logic_vector(3 downto 0);

WE : out std_logic);

end component;

component FOO2

port(A, B : in std_logic_vector(3 downto 0);

WE : in std_logic;

D : out std_logic_vector(3 downto 0);

ACT : out std_logic);

end component;

attribute syn_black_box of FOO2 : component is true;

attribute black_box_pad_pin of FOO2 : component is "D(3:0), ACT";

signal WE : std_logic;

begin

U0 : FOO1 port map (A => A, B => B1, C => C, WE => WE);

U1 : FOO2 port map (A => A, B => B2, WE => WE, D => D, ACT => ACTIVE);

end BEAVE;

Verilog - Using the "black_box_pad_pin" attribute

NOTE:

- This method is used with Synplify 5.0.7 and later.

- The "black_box_pad_pin" attribute is recognized for all families.

module FOO1 (A, B, C, WE);

input [3:0] A, B;

output [3:0] C;

output WE;

assign C = A + B;

assign WE = A[0] & A[1] & A[2] & A[3];

endmodule

module FOO2 (A, B, WE, D, ACT)

/* synthesis syn_black_box black_box_pad_pin="D[3:0],ACT" */;

input [3:0] A, B;

input WE;

output [3:0] D;

output ACT;

endmodule

module TOP (A, B1, B2, C, D, ACTIVE);

input [3:0] A, B1, B2;

output [3:0] C, D;

output ACTIVE;

wire WE;

FOO1 U0 (.A (A), .B (B1), .C (C), .WE (WE));

FOO2 U1 (.A (A), .B (B2), .WE (WE), .D (D), .ACT (ACTIVE));

endmodule

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