Handling Blockages

All blockages and their constraints are loaded when you read in a design. To change this default behavior, you can set the following environment variables prior to loading the design:

• db.load_blockages determines whether to load standard cell blockages that originated in LEF. Default is true.
• db.load_core_blockages determines whether to load core cell blockages (usually top-level) that originated in the blockage section in DEF. Default is true.
• db.enable_blockage_constraints determines whether constraints for blockage shapes are read in. Default is true.

By default, the minimum spacing required by blockages is used for block-to-neighboring shapes spacing, regardless of the spacing rules for the neighboring shapes. You can change the default behavior by using the set_treat_blockage_as_metal Tcl command. This command uses four arguments to determine the way that blockages are treated: min_width, min_space, override, and force_min_space.

• The min_space and min_width arguments are mutually exclusive. These arguments determine how blockages without any pre-assigned constraints are to be treated.
  • min_width causes the checker to treat all unassigned blockages as if they have an effective width equal to the minWidth rule for the current layer. Thus, the minimum spacing is determined based on the minWidth value.
  • min_space causes the checker to use the minSpacing rule for the current layer as the minimum spacing for all unassigned blockages.
• The override argument causes all pre-assigned constraints to be ignored and the min_width and min_space arguments determine the spacing to be used for all blockages.
• The force_min_space argument, when set to true, causes the checker to use the spacing required by blockages for blockage-to-neighboring shape spacing, rather than using the larger of the minimum spacing for the blockage and the neighboring shape.

Related Topics

Preparing the Routing Environment