nesting counters

[john]

Hi,

I need some guide lines to cascade three counters. I have two 5 bit
counters ( A and B) and one 14 bit counter ( C). Counter 'A' counts
upto 32 and increment Counter B by one and when counter B will reach to
32 it will increment counter C by one. The maximum count for counter C
is 256.
Should I increment the counter B at the falling edge of the MSB of the
counter A?
Should I increment the counter C on the falling edge of the counter B?

Please advice!
John

 

[Andrew FPGA]

Make sure you use the same clock for all the counters. Keep it
synchronous.
e.g. increment counter B when counter A = 31.

variable countB : natural range 0 to 31;
....

--Counter B
if rising_edge(clock) then
if countA = 31 then
countB := (CountB + 1) mod 32;
end if;
end if;

 

[john]

Hi,

Thanks for the reply! I was wondering that why do we need mod 32. would
u please advice me. Thanks
Regards
John

 

[Andrew FPGA]

Hi John,
Mod forces the rollover from 31 to 0. Actually XST(xilinx) won't
synthesise the mod operator if your count variable is not a power of 2
range. Instead you could test for the count = 31 and then assign 0 to
the count to achieve rollover.
Regards
Andrew

 

[john]

Hi,

I nee CountB, Count C and CountA are in different processes. How can I
make them shared in different processes. first I do not know how to
make them global. Advice needed! and then will it create any problems
later.

Thanks
John

 

[Mike Treseler]

I nee CountB, Count C and CountA are in different processes.

Why? Simpler is better.

How can I
make them shared in different processes.

Processes communicate using signals.
Look it up.

-- Mike Treseler

 

[john]

Hi,

But the problem is that my design needs to increment the counters on
the falling edge of the MSB bit. That will take the main clock away
from the counters and they will not be synchronous anymore. how can I
do it without removing the clock and on the falling edge of the MSB
bit.

John

 

[Mike Treseler]

But the problem is that my design needs to increment the counters on
the falling edge of the MSB bit. That will take the main clock away
from the counters and they will not be synchronous anymore. how can I
do it without removing the clock and on the falling edge of the MSB
bit.

Generate a synchronous strobe
and use that as an enable.

-- Mike Treseler

 

[john]

Can u advice me example code?

John

 

[Mike Treseler]

Can u advice me example code?

search for "strobe" here:
http://home.comcast.net/~mike_treseler/rise_count.pdf
http://home.comcast.net/~mike_treseler/rise_count.vhd

-- Mike Treseler

 

[john]

Hi,

The example u send me is little bit high level for me . Would you plz.
advice me that how can I add strobe signal to the counter. Right now I
have following counters. I have two 6 bit counters and one 14 bit
counter. I am using the 5th bit of the two counters as trigger to the
other counter. But I need something that can trigger the other counter
instantly. Because of this problem my whole project is not working
properly.


-- Frame Counter --
Process (Reset_out, DPR_CLK)
Begin
If (Reset_out ='1' )Then
Frame_cntr<=(others =>'0');

elsif rising_edge(DPR_CLK) then
If ( indicator_frame = '1') Then
Frame_cntr <= Frame_cntr + 1 ;
End If;
End If;
End Process;

Process (Reset_out, DPR_CLK)
Begin
If (Reset_out ='1') Then
countc_mux_datain <= (others =>'0');
elsif rising_edge(DPR_CLK) then
If (indicator_sample = '1') Then
countc_mux_datain <= countc_mux_datain + 1 ;
End If;
End If;
End Process;
indicator_frame <= countc_mux_datain (5) ;
-- Channel Counter routine Begins--
Process (Reset_out, DPR_CLK)
Begin

If( Reset_out ='1') Then
countb_mux_datain <= (others =>'0');

elsif rising_edge(DPR_CLK) then
if (incr_B='1') then
countb_mux_datain <= countb_mux_datain + 1;
End If;
End If;
End Process;

indicator_sample <= countb_mux_datain (5) ;

End DPR_ARCH;

Regards
John

 

[Uncle Noah]

Hi there

some 2-3 years ago i had implemented a parameterizable "hardware
looping unit" featuring (fully) nested counters for looping over such
loop structures. You can specify the number of loops and generate part
of the VHDL description from C generators.

You can reach it (OpenCores CVS) at:
http://www.opencores.org/projects.cgi/web/hwlu/overview

This is an implementation in VHDL of something similar to the
"Mediabreeze looping unit" by D. Talla.

kind regards
Nikolaos Kavvadias

 

[john]

Hi,

Thanks for ur reply! But I am unable to understand how to get the
example. Please advice me in m ore detail.

John

 

[john]

Hi Mike,

I have following questions

1. Why strobe?
2. Would you advice me that how can I generate the strobe signal to
enable the other counters?

Regards,
John

 

[Mike Treseler]

1. Why strobe?

This makes good use of the clock enable flops
and keeps things synched to one clock.

2. Would you advice me that how can I generate the strobe signal to
enable the other counters?

With an and gate and an inverter.
See the pdf link again.

-- Mike Treseler

 

[john]

Hi Mike,

So, i need to use the MSB bit of the first counter to "AND" with the
same MSB bit via an inverter to increment the second counter.

So, it will be count_B _indicator < = countA(4) AND NOT countA(4)

Am I right?

John

 

[Mike Treseler]

So, i need to use the MSB bit of the first counter to "AND" with the
same MSB bit via an inverter to increment the second counter.
So, it will be count_B _indicator < = countA(4) AND NOT countA(4)

Try it and see.

-- Mike Treseler

 

[john]

I tried but it did not work. its not incrementing the other counter. I
suspect that I am not understanding ur drawing correctly. Do u have two
counters in ur design?
John

 

[john]

Hi mike,

you know what you are a good guy. you sincerely wants to help people
who are doing VHDL. you might have scarificed alot to learn VHDL or
digital systems etc. But sometimes poeple like me who do not have
enough experience and skills in VHDL needs more than just help to solve
their problems. I know that u have enough experience to see the posting
on the goole groups that how much this person knows about the VHDL. So,
If you do not like the question or u think its too easy for u or for
whatever reason, please do not try to answer that question because when
other people see that u replied that question , they just do not help.
There are some people who do want to help me but they do not because
they see ur name. i hope, u will understand.

John

 

[Mike Treseler]

you might have scarificed alot to learn VHDL

I've always thought it was fun.
You might too if you focused on reading,
googling and learning simulation.

http://groups.google.com/groups?q=vhdl+count+process+enable+":="

-- Mike Treseler