1591 - Diamond / LatticeECP3: What is the guideline to use a general routing based clock for the LatticeECP3 device?
For the LatticeECP3 device, general routing can be used route as the clock resource rather than using dedicated clock resources. This should only be considered for non-critical clock paths and for small areas of the design. Clocks routed using the general data routing paths will not have the same performance as the dedicated routing resources. Due to the large amount of connectivity, this resource will not have a tight skew as the dedicated clocking resources. For this reason, it is best to limit the distance of clocks using general routing, as well as the number of loads. This can be done by grouping the logic in the clock domain with a UGROUP preference. As a result, it will improve both the setup time and the hold time for the general routing based clock.
If possible, user should always use a primary clock instead of the general routing based clock when routing a critical path clock for your design.
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