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After Place and Route

 
 
ec
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      01-02-2007
Hi

What if after Place and Route the timing constarint are lower then needed ,
what should be done ?

Should I generate another netlist , or should I try to change the VHDL code
of the model
and then to generate a new netlist and > new place and route ?

Thanks in advace
EC


 
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Mike Treseler
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      01-02-2007
ec wrote:

> What if after Place and Route the timing constarint are lower then needed ,
> what should be done ?


Your choices are
1. Reduce the clock frequency.
2. Pipeline the design.
3. Use a faster device.

-- Mike Treseler
 
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Thomas Stanka
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      01-03-2007

Mike Treseler schrieb:

> ec wrote:
>
> > What if after Place and Route the timing constarint are lower then needed ,
> > what should be done ?


First you should analyse the longest paths to have an idea why your
design miss your contraints. This could help you a lot in deceiding
what to do next.

> Your choices are
> 1. Reduce the clock frequency.
> 2. Pipeline the design.
> 3. Use a faster device.


2a) instead of real pipelining it is often possible to gain speed by
simple changes of your HW structure (eg. change state encoding, use
resource doubbling to improve timing, use downto-0 counter or lfsr
instead of up-to-constant counter,...). For complex fsm you _could_
gain a lot with major reworking if your first fsm design leads to high
fanout nets.

4. for slight violations you could
a) change the P&R until it fits (preplacing by hand can help a lot,
but don't expect miracles)
b) change the environmetal parameters if applicabel (e.g if your
voltage is in every case much better than worst case, you could
increase voltage for worst case timing analyses (if your tool allows to
do so))

5. rerun synthesis with other timing constraints (can help in _some_
cases, sometimes you can gain even with loose contraints)

6. Flatten Netlist, if it is still hierachically and your tool has some
weaknesses on module bounds.

4 -6 can do for up to ~30% depending on your design. If you want 100Mhz
and even miss 50 Mhz you typically need to use choices 1-3.

bye Thomas

 
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ec
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      01-03-2007
Thanks
ec

"Mike Treseler" <(E-Mail Removed)> ???
??????:(E-Mail Removed)...
> ec wrote:
>
>> What if after Place and Route the timing constarint are lower then needed
>> ,
>> what should be done ?

>
> Your choices are
> 1. Reduce the clock frequency.
> 2. Pipeline the design.
> 3. Use a faster device.
>
> -- Mike Treseler



 
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