6.11 Constraints by Name: Netlist Optimization

The following table shows which families support this constraint and which file formats and tools you can use to enter or modify it:

Use this constraint to remove all buffers and inverters from a given net. In the IGLOO and ProASIC3 architectures, inverters are considered buffers because all tile inputs can be inverted. This rule is also true for all Flash architectures but not for Antifuse architectures.

You can use one or more of the following commands or GUI tools to delete a buffer tree:

• PDC - delete_buffer_tree
• GCF - optimize

The following table shows which families support this constraint and which tools you can use to enter or modify it:

Use this constraint either to free up a dedicated clock routing resource by demoting a global net to a regular net or to prevent a clock net from automatically being promoted to a global net.

If there are multiple clocks in a design and not enough clock routing resources, you can demote a global net to a regular net for a clock that does not drive logic through the critical path in a design.

You can use one or more of the following commands or GUI tools to demote a clock net to a regular net:

• PDC - unassign_global_clock
• GCF - set_noglobal
• Compile Options - -demote_globals <value>

The following table shows which families support this constraint and which tools you can use to enter or modify it:

Use this constraint to increase the performance of your design.

If there are enough clock routing resources available in a device, you can promote regular nets that have high fan-out to the dedicated fast clock routing resources which can lead to better performance for your design.

You can use one or more of the following commands or GUI tools to promote a regular net to a global clock net:

• PDC - assign_global_clock
• GCF file - set_global (backwards compatible for ProASIC families only)
• Compile Options - -promote_globals <value>

The following table shows which families support this constraint and which file formats and tools you can use to enter or modify it:

Use this constraint to undo the operation of a previously specified delete_buffer_tree command. This constraint is useful in the import and merge flow when users want to keep the previous database constraint but want to overwrite just one delete_buffer_tree command.

You can use one or more of the following commands or GUI tools to restore a buffer tree:

• PDC - dont_touch_buffer_tree
• GCF - dont_optimize

The following table shows which families support this constraint and which tools you can use to enter or modify it:

Use this constraint to preserve instances before compiling them so they will not be combined during compile.

You can use the following command to preserve instances:

• PDC - set_preserve