Rising edge of the clock

[john]

Hello,


The problem is that the "Q(0)" bit of the counter is not incrementing
at the rising edge of the "inc" signal instead its incrementing when
"inc" signal goes from high to low. I want to increment Q(0) at rising
edge of the "clk" and rising edge of the signal "inc".
Please Advice!!
Thanks
john


The code is given below:

C0: counter port map (Data_out_bus(13 downto 0),DPR_CLK,inc,eq_signal,Reset_A);

Process ( State, input_signal )

Begin

Case State is


When E0 =>
Reset_A <='1';
inc <='0';
nextstate <=E1;


When E1 =>

Reset_A <='0';
inc <='1';

nextstate <=E2;

When E2 =>
Reset_A <='0';
inc <='0';

nextstate <=E1;


When others =>
nextstate <=E0;

End Case;

End Process;


-- ( 14 bit )


Entity counter is

Port (

Qout : out unsigned (13 downto 0);
CLK : in std_logic;
P : in std_logic;
count_equal: out std_logic;
Reset_c: in std_logic


);

End counter;

Architecture count_arch of counter is

Signal Q : unsigned (13 downto 0);

Begin

count_equal <= Q(0);


Process (Clk, Reset_c)

Begin


If (Reset_c = '1' ) then

Q( 13 downto 0 ) <= ('0', '0', '0', '0', '0', '0', '0',
'0', '0', '0', '0', '0', '0', '0' );


Elsif ( Clk 'event and Clk='1' ) then

If (P= '1') then

Q <= Q + 1;

Qout <=Q;

End If;

End if;

End process;

End count_arch ;

 

[Neo]

Hello,


The problem is that the "Q(0)" bit of the counter is not incrementing
at the rising edge of the "inc" signal instead its incrementing when
"inc" signal goes from high to low. I want to increment Q(0) at rising
edge of the "clk" and rising edge of the signal "inc".
Please Advice!!
Thanks
john


The code is given below:

C0: counter port map (Data_out_bus(13 downto 0),DPR_CLK,inc,eq_signal,Reset_A);

Process ( State, input_signal )

Begin

Case State is


When E0 =>
Reset_A <='1';
inc <='0';
nextstate <=E1;


When E1 =>

Reset_A <='0';
inc <='1';

nextstate <=E2;

When E2 =>
Reset_A <='0';
inc <='0';

nextstate <=E1;


When others =>
nextstate <=E0;

End Case;

End Process;


-- ( 14 bit )


Entity counter is

Port (

Qout : out unsigned (13 downto 0);
CLK : in std_logic;
P : in std_logic;
count_equal: out std_logic;
Reset_c: in std_logic


);

End counter;

Architecture count_arch of counter is

Signal Q : unsigned (13 downto 0);

Begin

count_equal <= Q(0);


Process (Clk, Reset_c)

Begin


If (Reset_c = '1' ) then

Q( 13 downto 0 ) <= ('0', '0', '0', '0', '0', '0', '0',
'0', '0', '0', '0', '0', '0', '0' );


Elsif ( Clk 'event and Clk='1' ) then

If (P= '1') then

Q <= Q + 1;

Qout <=Q;

End If;

End if;

End process;

End count_arch ;

John,
here you have single register pipeline which is introducing a clock
delay. you are reading incr which is generated w.r.t to clock in
another clocked process which is causing the delay. directly run you
counter in the states to avoid this delay.

-Neo

 

[Thomas Stanka]

The problem is that the "Q(0)" bit of the counter is not incrementing
at the rising edge of the "inc" signal instead its incrementing when
"inc" signal goes from high to low. I want to increment Q(0) at rising
edge of the "clk" and rising edge of the signal "inc".

I can't see your intention in the code below. To detect rising edges
synchron you use a shift register.

test_sr<=test_sr(0)&test_sig
test_edge<=test_sr(0) and not test_sr(1)

The problem with your code is, that your counter increments, at the
next rising edge of clk while inc=1. If inc changes with your clock
for one clock cycle (can't see in your code, when inc will change in
relation to CLK) you will see that Q changes with inc but delayed for
one cycle. A good example why it could be better to use a small
gatedelay (after 1 ns), to see signals changing delayed to clock.

Q( 13 downto 0 ) <= ('0', '0', '0', '0', '0', '0', '0',
'0', '0', '0', '0', '0', '0', '0' );

Q<=(others=>'0') seems more readable to me and has the same semantics.

 

[Mohammed khader]

john wrote :

"inc" signal goes from high to low. I want to increment Q(0) at rising
edge of the "clk" and rising edge of the signal "inc".
Please Advice!!

I did'nt understand why do you want to check 2 rising edge .It is
highly impractical .... According to me P is used as Enbale signal
for the counter....

If you intend to do then use nested rising edge if statements as
follows..
if(clk=1 and clk'Event)then
if(p=1 and p'Event)then
Q <=Q+1 ;
end if ;
end if ;

There are many more things to note ...

Qout <=Q;

Qout is inside the Clocked process so Output is one clock cycle
delayed.

Check the use of OTHERS keyword and try to use it for assinging long
words.. like in

If (Reset_c = '1' ) then

Q( 13 downto 0 ) <= ('0', '0', '0', '0', '0', '0', '0',
'0', '0', '0', '0', '0', '0', '0' );

Code for the state Machine is not clear and complete But it looks
like you are reseting the Conter after every increment...

 

[john]

Hi Neo,

The state machine and the counter has the same clock. So, If two
processes have same clock then still they have delay between them.
Plus would u please explain that how am I using the single register
pipeline.
Please Advice!

Thanks
John

 

[rickman]

Hi Neo,

The state machine and the counter has the same clock. So, If two
processes have same clock then still they have delay between them.
Plus would u please explain that how am I using the single register
pipeline.
Please Advice!

Thanks
John

Here you have a register to clock in all the data bits, but the output
is delayed by another clock cycle to transfer it to the Qout register.
So the output changes two enabled clocks after the data is input. What
exactly are you trying to do?

--

Rick "rickman" Collins

(e-mail address removed)
Ignore the reply address. To email me use the above address with the XY
removed.

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design URL http://www.arius.com
4 King Ave 301-682-7772 Voice
Frederick, MD 21701-3110 301-682-7666 FAX

 

[Thomas Stanka]

If you intend to do then use nested rising edge if statements as
follows..
if(clk=1 and clk'Event)then
if(p=1 and p'Event)then
Q <=Q+1 ;
end if ;
end if ;

I don't believe, that this piece of code will synthesis correctly.
Never use two clocks in one process for synthesisable code.

bye Thomas

 

[Mohammed khader]

I don't believe, that this piece of code will synthesis correctly.
Never use two clocks in one process for synthesisable code.

Hi Thomsa,

I did'nt say that " code will synthesis correctly". I said it is
hight impractical for this . If any one wants to just simulate then
will .

 

[Pieter Hulshoff]

The problem is that the "Q(0)" bit of the counter is not incrementing
at the rising edge of the "inc" signal instead its incrementing when
"inc" signal goes from high to low. I want to increment Q(0) at rising
edge of the "clk" and rising edge of the signal "inc".
Please Advice!!

Ok, here's a few examples:

1. Assumption: inc is generated on the same clock as the counter process:

PROCESS
BEGIN
WAIT UNTIL clk = '1';
inc_d <= inc;
IF inc = '1' AND inc_d = '0' THEN
Q <= Q + 1;
END IF;
Qout <= Q;
IF reset = '1' THEN
Q <= (OTHERS => '0');
Q_out <= (OTHERS => '0');
inc_d <= '0';
END IF;
END PROCESS;

2. Assumption: inc is generated on another clock as the counter process:

PROCESS
BEGIN
WAIT UNTIL clk = '1';
inc_c2c <= inc;
inc_meta <= inc_c2c;
inc_d <= inc_meta;
IF inc_meta = '1' AND inc_d = '0' THEN
Q <= Q + 1;
END IF;
Qout <= Q;
IF reset = '1' THEN
Q <= (OTHERS => '0');
Qout <= (OTHERS => '0');
inc_c2c <= '0';
inc_meta <= '0';
inc_d <= '0';
END IF;
END PROCESS;

Regards,

Pieter Hulshoff

 

[Wong]

I don't believe, that this piece of code will synthesis correctly.
Never use two clocks in one process for synthesisable code.

bye Thomas

Yes, I am totally agree. I don't think this is going to work since you
are detecting both rising edge at the same time exactly.