18.104.22.168. Planning Physical Implementation
- The number of unique clock domains and their relationships
- The amount of logic in each functional block
- The location and direction of data flow between blocks
- How data routes to the functional blocks between I/O interfaces
Interface-wide control or status signals may have competing or opposing constraints. For example, when a functional block's control or status signals interface with physical channels from both sides of the device. In such cases you must provide enough pipeline register stages to allow these signals to traverse the width of the device. In addition, you can structure the hierarchy of the design into separate logic modules for each side of the device. The side modules can generate and use registered control signals per side. This simplifies floorplanning, particularly in designs with transceivers, by placing per-side logic near the transceivers.
When adding register stages to pipeline control signals, turn off Auto Shift Register Replacement in the Assignment Editor (Assignments > Assignment Editor) for each register as needed. By default, chains of registers can be converted to a RAM-based implementation based on performance and resource estimates. Since pipelining helps meet timing requirements over long distance, this assignment ensures that control signals are not converted.
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