Handling of Low Power Special Cells

The 1801 import flow supports the following low power special cells:

• Level Shifter
  Import 1801 flow supports different level shifter configurations, such as single rail, dual rail and enabled single /dual rail (combo cell). For each level shifter instance, the load and drivers along with their power domains are determined and the netSet properties are created based on the criteria mentioned below.
  • If a level shifter cell is connected to a standard cell or port at both ends, the load and driver domains are used to resolve PG connections.
  • If a level shifter instance is a multi-rail cell, the driver domain resolves the input supply connections and the load domain resolves the output supply connections. Level shifter rule specified in the input 1801 file enables in determining the load and the driver domains. The rule is considered to find the supply set based on input_supply_set and output_supply_set argument. Level shifter rules are specified in input 1801 as:
    

    set_level_shifter ls_rule -domain pd_ls -applies_to inputs -rule low_to_high -location self -input_supply_set SS_VDD_VSS -output_supply_set SS_VDDA_VSS

    If not specified, Power Manager finds the driver and load supply set for the level shifter by traversing the design path and resolving the connectivity accordingly.
  • If a level shifter instance is a single-rail cell, the load domain resolves the output PG connections. input_signal_level is required in the Liberty model of the level shifter to identify the cell type as single rail level shifter.
  • If a level shifter instance is connected to an isolation cell at one end, the load or driver domain on the other end is determined. If the driver domain is known, it resolves the input supply connections. If the load domain is known, it resolves the output supply connections.
    
    A single-rail level shifter cell has only output supply.
  • If a level shifter instance is connected to an isolation cell at one end, the power domain for the end connected to the isolation instance is determined from the isolation instance. Therefore, the power domain at the isolation cell intersection is the same as the power domain of the isolation cell itself.
• Isolation Cell
  Initially, the load and driver of the isolation cell are traced and then, the netSet properties are created based on the criteria mentioned below.
  • If an isolation cell is connected to a standard cell or a port on both the ends, the power domains of the load as well as the driver are used to resolve the PG connections and create netSet properties.
  • If an isolation cell instance is a multi-rail cell and has a switchable power or ground pin, then the switchable domain is used to resolve the switchable PG connections. The non-switchable domain resolves the non-switchable PG connections.
  • If an isolation cell instance is a single-rail isolation cell, only one of the load or driver domain that is non-switchable is used to resolve the PG connections. The isolation rule specified in input 1801 file assists in determining the load and the driver domains. The rule will be considered to find a supply set based on isolation_supply_set defined in the isolation rule. Isolation rules are specified in input 1801 file as:
    

    set_isolation ISO -domain PD_VDD_VSS -location self -elements {I1/In} -isolation_supply_set SS_VDD_VSS -isolation_signal I0/en -isolation_sense high -location self

    
    
    isolation_supply_set is required if default_isolation is not mentioned in the power domain stated in the input 1801 file.
    You can provide an expression containing multiple pins for enable in the tech.upf file for isolation cells and level shifter cells. For example, define_isolation_cell -cells ISOHX1_OFF -enable "EN1&EN2&!EN3" -power VDD -ground VSS.
• Power Switch
  For power switch, the load and drivers supply along with the control net are determined and the netSet properties are created accordingly. The power switch rule specified in input 1801 file enables in determining the load and the driver domains. The rule is considered to find a supply set based on input_supply_port, output_supply_port and control_port.
  Power switch rules are specified in the input 1801 file as:

  create_power_switch I3_I0 -output_supply_port { VDD VDDSW } -input_supply_port { ExtVDD VDD } -control_port { PSO    psw_en } -on_state { on ExtVDD {!PSO} } -off_state { off PSO } -domain PD_TOP

  If the create_power_switch has a -instance option, the name of the switch instance(s) are provided that are covered by the power switch rule. If the create_power_switch has a -domain option, the power switch rule targets all power switches that are inserted within the domain boundary.

Related Topics

Importing Power Intent

Redirected netSet Property Creation and Optimization

Tie Connection Resolution

Support of Hierarchical 1801 for Import Flow

Removing Imported Power Intent