Setting Net Priorities

Use net priorities to more directly route critical nets or any given net. There are eleven levels of priority with 0 as the lowest priority and 10 as the highest priority. Net priorities can be set in DEF and by some data translation utilities. Unless you know that there are previously set net priorities that you want to keep, it is advisable to reset all net priorities prior to setting a few. The priority is relative, therefore, setting a net priority to 10 does nothing more than setting it to 1 over a default of 0. You can set net priorities for all nets, a given net, or nets in a set.

To reset the net priority for all nets, use

set_net_priority -all -priority 0

To set the net priority to 1 for all nets whose names begin with data_input_bus, use

replace_set -set1 [find_net -name {data_input_bus*} -ignore_case true -no_wildcard false ] -set2 [get_selection_set]
set_net_priority -set [get_selection_set] -priority 1

The global router, conduit router, and detail router will honor net priorities. Nets with priorities greater than zero will be sorted and the nets with the highest priority will be routed first, thereby placing them close to their ideal position. During conduit routing, priority on nets with long segments will be more effective than priority on short nets because the primary goal of the conduit router is to track assign long route segments. Short segments are better handled by the detail router. At each of these three stages of routing—global, conduit, and detail—priority nets are routed first, followed by all other nets. Priority nets, if set judiciously, should maintain their ideal topology through the routing flow. However, priority nets can be rerouted in order to cleanly complete other connections.

If a net is long due to some other constraint, you can apply your own formula to determine when the routing of a net is unacceptable and then re-route it using global_route -mode eco. Use report_net_stats and the Net Manager to determine the quality of the length of the net.

Related Topics

Preparing the Routing Environment