Instantiation - 2022.1 English

UltraFast Design Methodology Guide for Xilinx FPGAs and SoCs (UG949)

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2022.1 English

The most low-level and direct method of controlling clocking structures is to instantiate the desired clocking resources into the HDL design. This allows you to access all possible capabilities of the device and exercise absolute control over them. When using BUFGCE, BUFGMUX, BUFHCE, or other clocking structure that requires extra logic and control, instantiation is generally the only option. However, even for simple buffers, sometimes the quickest way to obtain a desired result is to be direct and instantiate it into your design.

An effective style to manage clocking resources (especially when instantiating) is to contain the clocking resources in a separate entity or module instantiated at the top or near the top of the code. By having it at the top-level of code, it may more easily be distributed to multiple modules in your design.

Be aware of where clocking resources can and should be shared. Creating redundant clocking resources is not only a waste of resources, but generally consume more power, create more potential conflicts and placement decisions resulting in longer overall implementation tool compile times and potentially more complex timing situations. This is another reason why having the clocking resources near the top module is important.

Tip: You can use Vivado HDL templates to instantiate specific clocking primitives.