FIFO simulation

[ALuPin]

Hi,

I have generated a FIFO with output registers and one without
output registers. (Altera QuartusII MegaWizardManager)

And yet when simulating both in Modelsim(functional simulation)I get
the same result: The data appear on the output of the FIFO immediately
after asserting the rdreq.

Any ideas what could be wrong ?

Here is my testbench code:

ibrary ieee;

use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;

entity tb_fifo_test_unregistered is
end tb_fifo_test_unregistered;


architecture testbench of tb_fifo_test_unregistered is

component fifo_test_unregistered
port ( Data : in std_logic_vector(8 downto 0);
Wrreq : in std_logic;
Rdreq : in std_logic;
Clock : in std_logic;
Aclr : in std_logic;
Q : out std_logic_vector(8 downto 0)
);

end component;

signal t_data : std_logic_vector(8 downto 0);
signal t_wrreq : std_logic;
signal t_rdreq : std_logic;
signal t_clock : std_logic;
signal t_clock2 : std_logic;
signal t_aclr : std_logic;
signal t_q : std_logic_vector(8 downto 0);

begin

uut : fifo_test_unregistered
port map ( Data => t_data,
Wrreq => t_wrreq,
Rdreq => t_rdreq,
Clock => t_clock2,
Aclr => t_aclr,
Q => t_q
);

process
begin
t_clock <= '1'; wait for 5.5 ns;
t_clock <= '0'; wait for 5.5 ns;
end process;

process
begin
t_clock2 <= '0'; wait for 5.5 ns;
t_clock2 <= '1'; wait for 5.5 ns;
end process;



process
begin
t_aclr <= '1', '0' after 103 ns;
wait;
end process;



process
begin
t_data <= (others => '0');
t_wrreq <= '0';
t_rdreq <= '0';

for i in 0 to 40 loop
wait until rising_edge(t_clock);
end loop;

for i in 0 to 31 loop
wait until rising_edge(t_clock);
t_wrreq <= '1';
t_data <= conv_std_logic_vector(i+1, 9);
end loop;

t_wrreq <= '0';

for i in 0 to 10 loop
wait until rising_edge(t_clock);
end loop;

for i in 0 to 31 loop
wait until rising_edge(t_clock);
t_rdreq <= '1';
wait until rising_edge(t_clock);
t_rdreq <= '0';
wait until rising_edge(t_clock);
end loop;
t_rdreq <= '0';

wait;
end process;


end testbench;

 

[Neo]

Nothing is wrong with the test bench but you have not put the
registered fifo code here. cant make out anything without the rtl.

 

[ALuPin]

Here is the code for registered one:

LIBRARY ieee;
USE ieee.std_logic_1164.all;

LIBRARY altera_mf;
USE altera_mf.altera_mf_components.all;

ENTITY fifo_test_registered IS
PORT
(
data : IN STD_LOGIC_VECTOR (8 DOWNTO 0);
wrreq : IN STD_LOGIC ;
rdreq : IN STD_LOGIC ;
clock : IN STD_LOGIC ;
aclr : IN STD_LOGIC ;
q : OUT STD_LOGIC_VECTOR (8 DOWNTO 0)
);
END fifo_test_registered;


ARCHITECTURE SYN OF fifo_test_registered IS

SIGNAL sub_wire0 : STD_LOGIC_VECTOR (8 DOWNTO 0);



COMPONENT scfifo
GENERIC (
lpm_width : NATURAL;
lpm_numwords : NATURAL;
lpm_widthu : NATURAL;
intended_device_family : STRING;
lpm_type : STRING;
lpm_showahead : STRING;
overflow_checking : STRING;
underflow_checking : STRING;
use_eab : STRING;
add_ram_output_register : STRING
);
PORT (
rdreq : IN STD_LOGIC ;
aclr : IN STD_LOGIC ;
clock : IN STD_LOGIC ;
q : OUT STD_LOGIC_VECTOR (8 DOWNTO 0);
wrreq : IN STD_LOGIC ;
data : IN STD_LOGIC_VECTOR (8 DOWNTO 0)
);
END COMPONENT;

BEGIN
q <= sub_wire0(8 DOWNTO 0);

scfifo_component : scfifo
GENERIC MAP (
lpm_width => 9,
lpm_numwords => 32,
lpm_widthu => 5,
intended_device_family => "Cyclone",
lpm_type => "scfifo",
lpm_showahead => "OFF",
overflow_checking => "ON",
underflow_checking => "ON",
use_eab => "ON",
add_ram_output_register => "ON"
)
PORT MAP (
rdreq => rdreq,
aclr => aclr,
clock => clock,
wrreq => wrreq,
data => data,
q => sub_wire0
);
END SYN;




And here is the code for the non-registered one:





LIBRARY ieee;
USE ieee.std_logic_1164.all;

LIBRARY altera_mf;
USE altera_mf.altera_mf_components.all;

ENTITY fifo_test_unregistered IS
PORT
(
data : IN STD_LOGIC_VECTOR (8 DOWNTO 0);
wrreq : IN STD_LOGIC ;
rdreq : IN STD_LOGIC ;
clock : IN STD_LOGIC ;
aclr : IN STD_LOGIC ;
q : OUT STD_LOGIC_VECTOR (8 DOWNTO 0)
);
END fifo_test_unregistered;


ARCHITECTURE SYN OF fifo_test_unregistered IS

SIGNAL sub_wire0 : STD_LOGIC_VECTOR (8 DOWNTO 0);



COMPONENT scfifo
GENERIC (
lpm_width : NATURAL;
lpm_numwords : NATURAL;
lpm_widthu : NATURAL;
intended_device_family : STRING;
lpm_type : STRING;
lpm_showahead : STRING;
overflow_checking : STRING;
underflow_checking : STRING;
use_eab : STRING;
add_ram_output_register : STRING
);
PORT (
rdreq : IN STD_LOGIC ;
aclr : IN STD_LOGIC ;
clock : IN STD_LOGIC ;
q : OUT STD_LOGIC_VECTOR (8 DOWNTO 0);
wrreq : IN STD_LOGIC ;
data : IN STD_LOGIC_VECTOR (8 DOWNTO 0)
);
END COMPONENT;

BEGIN
q <= sub_wire0(8 DOWNTO 0);

scfifo_component : scfifo
GENERIC MAP (
lpm_width => 9,
lpm_numwords => 32,
lpm_widthu => 5,
intended_device_family => "Cyclone",
lpm_type => "scfifo",
lpm_showahead => "OFF",
overflow_checking => "ON",
underflow_checking => "ON",
use_eab => "ON",
add_ram_output_register => "OFF"
)
PORT MAP (
rdreq => rdreq,
aclr => aclr,
clock => clock,
wrreq => wrreq,
data => data,
q => sub_wire0
);



END SYN;

 

[Neo]

Well, its a macro so cant do much. try checking out the attributes of
the macro. But do you mean the output is available in the same cycle
the signal "rdreq" is aaeerted?

 

[ALuPin]

Yes, in both simulations.

Of course I have instantiated "fifo_test_registered" in my testbench
for the
registered version.

Rgds
André

 

[info_]

Have you checked the documentation waveform that Quartus II
Megawizzard does generate for you to illustrate the behavior
of the generated macro ?

Simulating is still definitely a good idea...
however, I think you are changing rdreq just at the clock's rising edge,
which might be legit if you don't have any delta delay (which is hard
to assess in a macro model) but which makes the waveform harder to
interpret anyway.
I suggest you change your inputs at the clock's inactive (falling) edge.

Bert Cuzeau