Scoped Queries Guidelines - 2022.1 English

For this flow to work smoothly, the XDC constraints must be written so that the effects of the constraints stay local to the IP or sub-module instance. The Vivado tools can set the scope of queries to a specific level of the hierarchy as seen previously in Constraints Scoping. When developing constraints for an IP or a sub-level module, you must understand the behavior of the query commands:

• Cell/net/pin objects queries are limited to the scoped instance and its sub-levels:
  • get_cells/get_nets/get_pins <name pattern>
  • The NAME property of the object shows the full hierarchical path of the object relative to the top-level and not just the scoped instance. If you use the -filter option of the get_* commands on the NAME property, you must use the glob string match operator and provide a pattern which starts with a *. For example:

    get_nets -hierarchical -filter {NAME =~ *clk}

• get_ports returns a top-level port if the port of the block/IP is directly connected to a top-level port. Otherwise, get_ports returns a hierarchical pin.
• Netlist helper commands are also scoped:
  • all_ffs, all_latches, all_rams, all_registers, all_dsps, all_hsios return only instances included in the current instance.
• IO helper commands cannot be used at all in a scoped XDC:
  • all_inputs, all_outputs
• Clock commands are not scoped and will return all timing clocks of your design.
  • get_clocks, all_clocks
• Top-level and local clock objects can be queried by probing the netlist with get_clocks -of_objects.
  • Retrieve a clock entering the current instance by using get_clocks -of_objects [get_ports <interfacePinName>].
  • Retrieve a clock automatically generated inside the current instance by using get_clocks -of_objects [get_pins <instName/outPin>], where instName is a clock generator instance.
• Querying any object in the design is possible using the -of_objects option:
  • Example: get_pins -leaf -of_objects [get_nets local_net]
• Queries are supported for top-level ports connected to the current instance interface nets:

  get_ports -of_objects [get_nets <scoped_instance_net>]

• Queries of IP/sub-module interface pins are not allowed:
  • “get_pins clk” returns an error.
• Path tracing commands are also scoped:
  • all_fanin/all_fanout traverses the scoped design and stops at its boundary.
• Use get_cells/get_pins/get_nets with the most specific pattern instead of using the all_registers command with the -clock option to query all the cells connected to a particular clock. The returned list can be very large while only a few objects need to be constrained. This can impact the runtime negatively.