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how to meet timing constraints

 
 
ra
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      10-08-2004
Hi all,
I'm approaching the hardware world (I'm a software engineer), and
developing a system on a Xilinx FPGA (VirtexIIP) using ISE 6.2. I'd like
to know if there is a good book or some other source of information
about what to do if timing constraints are not met (where to look for
information, how to interpret them, what to change, etc. I have some
vague ideas, obtained from Xilinx support, but I'm looking for a more
comprehensive document on the topic.

Thank You

RA
 
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Barry Brown
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      10-08-2004
At the Xilinx website, under education, there is a free online training
class about "Timing Closure Flow". Might be worth a look.


"ra" <(E-Mail Removed)> wrote in message news:r%p9d.209790$D%.148713@attbi_s51...
> Hi all,
> I'm approaching the hardware world (I'm a software engineer), and
> developing a system on a Xilinx FPGA (VirtexIIP) using ISE 6.2. I'd like
> to know if there is a good book or some other source of information
> about what to do if timing constraints are not met (where to look for
> information, how to interpret them, what to change, etc. I have some
> vague ideas, obtained from Xilinx support, but I'm looking for a more
> comprehensive document on the topic.
>
> Thank You
>
> RA



 
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Ralf Hildebrandt
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      10-09-2004
ra wrote:


> about what to do if timing constraints are not met (where to look for
> information, how to interpret them, what to change, etc.


Synthesis tools can report the "longest path" to you. They will print an
information where the path starts and where it ends. Start and end are
flipflops (or sometimes latches) in most cases.
Normally these FFs can be identified by their names and one can find
them in the VHDL source code. Now it is your part to understand, why
this delay path from the startpoint to the endpoint is so long. (In most
cases one will have a big bunch of combinational logic.)
Once you have identified the reason, you can think about a solution
(pipelining, (functional) easier description of this block...).

It may be helpful to split a design in some smaller components and
synthesize them separately. Understanding and finding the delay paths
may be easier, because you don't have to search them in a huge complex
block.

Ralf
 
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