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Visitor
Visitor
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Registered: ‎04-09-2019

how to optimise long carry8 chain on vcu1525

I am having problem with long carry8 chain,

Due to which design fails in timing when clock freq is 500mhz.

Can someone please suggest any workaround.

RTL for problem.

reg [255:0] hash;

reg[255:0] target

If(hash <= target)

     valid_nonce <= 1;

else

   valid_nonce <= 0;

I have attached screenshot

Thanks and regards

Screenshot from 2019-10-21 23-27-47.png
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Moderator
Moderator
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Registered: ‎03-16-2017

Re: how to optimise long carry8 chain on vcu1525

@abdullahlokh 

Some suggestions: 

1. Use the FewerCarryChains synthesis directive, or set the CARRY_REMAP property on the cells to be removed by opt_design.

2. Add pipelining registers to reduce logic levels. 

3. Run report QoR suggestions in Vivado GUI and observe the suggestions and apply accordingly. Check UG906 (page 154 onwards) for more info. on it. https://www.xilinx.com/support/documentation/sw_manuals/xilinx2019_1/ug906-vivado-design-analysis.pdf

 

 

 

Regards,
hemangd

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