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Observer a9909928
Observer
3,225 Views
Registered: ‎02-16-2011

Register the inputs and outputs of your design????

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Hello everyone,

 

I read the documents " System generator DSP for user". There is one section said register the inputs and outputs of you design could enhance FPGA performance. Can someone tell me reasons for that ?

 

These are origional texts:

 

Register inputs and outputs of your design. This can be done by placing a Delay block

having latency 1 or a Register block after the Gateway In and before Gateway Out blocks.

Selecting any of the Register block features adds hardware.

Double registering the I/Os may also be beneficial. This can be performed by instantiating

two separate Register blocks, or by instantiating two Delay blocks, each having latency 1.

This allows one of the registers to be packed into the IOB and the other to be placed next to

the logic in the FPGA fabric. A Delay block with latency 2 does not give the same result

since this block is implemented using an SRL16 and cannot be packed into an IOB.

 

 

 

Thanks a lot.

 

Regards

 

Ryan

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Xilinx Employee
Xilinx Employee
3,975 Views
Registered: ‎01-03-2008

Re: Register the inputs and outputs of your design????

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> Can someone tell me reasons for that ?

 

Because if you don't register your inputs and outputs you will end up with very long input setup, input hold and clock-to-output delays that will vary from implementation to implementation resulting in a system that does not work.

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Xilinx Employee
Xilinx Employee
3,976 Views
Registered: ‎01-03-2008

Re: Register the inputs and outputs of your design????

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> Can someone tell me reasons for that ?

 

Because if you don't register your inputs and outputs you will end up with very long input setup, input hold and clock-to-output delays that will vary from implementation to implementation resulting in a system that does not work.

------Have you tried typing your question into Google? If not you should before posting.
Too many results? Try adding site:www.xilinx.com
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Instructor
Instructor
3,222 Views
Registered: ‎08-14-2007

Re: Register the inputs and outputs of your design????

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Also the suggestion to use two registers helps to meet timing in larger parts.  When you

use a register in the IOB, you are constraining the register to a specific location

related to that pin, usually at the edge of a chip (some flip-chip parts also have I/O

in the middle of the die).  Routing from this register to the rest of the logic can then

be quite long.  An additional register allows the placement tools to break up the

routing delay over two clock periods, making it easier to find a good timing placement

for the bulk of the design, which usually likes to concentrate near the center of the

die.

 

-- Gabor

-- Gabor
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