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Subject: Simulating multicycle paths on the Palladium
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tom paulson
moderator
Posts: 4
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4/11/2007 3:37 PM  
We are starting to experiment with a technique to simulate multicycle paths on the Palladium. Our definition of a multicycle path is a path from flip-flop A to flip-flopB where the timing in the path exceeds one clock cycle as shown by the timing analysis tool. These paths must either be re-designed to meet the one clock cycle criteria, or be assured that the data from flop-flopA will change at most every other clock cycle.

There are 3 steps to this process:
1. We have defined our system clock to be made-up of 4 qtfclks. One qtfclk is the basic Palladium clock, and is used to defined your clock signals.
2. The Palladium has a flip-flop that is clocked the qtfclk. We made up a verilog module that uses six of these flip-flops to produce a 6 qtfclk delay. This delay corresponds to a 1-1/2 clock cycle delay.
3 We then instantiate our verilog module in the path from flip-flopA to flip-flopB and run tests on the Palladium.

The early result show that we are achieiving the expected delays, and so far the test are running.
volker.wegner
Posts: 4
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4/19/2007 12:05 AM  
Hi Tom,

your description is correct and Palladium can handle multicycle paths in the way you described it.

However, your step 1) is NOT a prerequisite for enabling multicycle paths. Your design or environment may require a 4 to 1 ratio between fclk and fastest design clock but this would be a very rare case and it is absolutely NOT a requirement to enable multicycle paths. Multicycle paths are also possible with a 2/1 or even 1/1 ratio between fclk and fastest design clock, giving a speedup of up to 4x over your current environment.

Also I would suggest to use the qel command breakNet rather than inserting delay-flops. This would allow keeping the RTL as is, rather than modifying it.

Off course, when modeling multicycle paths within a 2x or 1x environment, the number of fclk-delays outlined in step 2) need to be reduced accordingly. In 2x mode you would need 2 or 3 fclks delays while in 1x mode you would need 1fclk delay.

I write this to make sure nobody misreads the original post.

Best regards, Volker
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Forums > Functional Verification > Simulation, Acceleration, Emulation > Simulating multicycle paths on the Palladium


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