A common cause of implementation issues is failing to account for explicit and implicit physical constraints:
- Explicit physical constraints
- Examples include the pinout, which directly constrains logic placement.
- Implicit physical constraints
- Certain specialized resources are available only in specific device locations,
influencing placement. Examples include:
- I/Os
- Gigabit transceivers
- DSP slices
- Block RAM
- Clock management blocks such as MMCM
- Clock buffers such as BUFG
Blocks that consume large amounts of these specialized resources might need to be spread across the device, which affects placement and routing for the rest of the design.
Pblocks are explicit physical constraints that define allowable placement areas for specified logic. To analyze block resource usage on the device, use one or more of these methods:
- Report utilization
- Netlist properties
- Pblock properties