Latency Difference Synthesis, CoSIM

[j_ney]

Hello!

I've implemented a Convolutional Neural Network in HLS and I'm wondering why there is a large difference between reported Synthesis Latency and Co-Simulation Latency. 

Synthesis reports 2664575 Clock Cycles while Co-Sim reports 6712380.

The Synthesis Latency is the one I would expect when theoretically calculating the latency of the different layers. 

When I run the Network on-board I also get the Co-Sim Latency. 

What does Co-Sim take into account that Synthesis doesn't? I've read that it also simulates AXI-Master accesses, so I changed the bit-width of my input and output to test if it changes something, but latency stays the same. Is there something else Co-Sim additionally simulates?

Best regards 

Jonas

[nithink]

@j_ney The latency values provided after c-synthesis are static values based on the shortest and longest path in the design. The values shown after co-sim are the values based on the simulation data set and are the actual values which you need to look at

Thanks,

Nithin

[j_ney · Accepted solution]

In my case the solution to the problem was the depth of the HLS streams. 

I've implemented a design with dataflow between functions and using higher depth for the streams between functions, I can achieve the latency given by synthesis. 

It seems like synthesis assumes infinite FIFO depth for the latency calculation. 

Best regards

Jonas