Special Isolation Cells in Liberty Power Model Export

Ports connected to NOR or NAND type isolations cells must be handled carefully in the Libert power model export flow to ensure there are enough attributes to indicate related power or ground for actual data receivers in a megacell or to indicate that enable pins cannot be off in the partial power down state.

The following three scenarios are addressed in the tool while handling ports connected to isolation cells:

• Input ports connected to NOR/NAND isolation cell data pins
  • No changes are made to the related_power_pin or related_ground_pin attribute values.
  • The alive_during_power_up attribute is added if a NOR/NAND isolation cell has inverted input. This ensures that the input cannot be floating when ports related power and ground pins are on.
  • The isolation_sink_power_pin and isolation_sink_ground_pin attributes are added to indicate related power/ground pins for a data receiver inside a megacell.
• Input ports connected to NOR/NAND isolation cell enable pins
  • When the value of updateRelatedSuppliesForNorNandIsoPorts = t.
    • If the sink of the isolation cell is some logic visible inside a macro, the related_power_pin or related_ground_pin values are updated based on the supply powering the logic connected to the isolation output. The alive_during_partial_power_down or permit_power_down attributes are not added.
    • If the immediate fanout of an isolation cell is a top-level port, there is no change made to the related_power_pin / related_ground_pin attribute values. The alive_during_partial_power_down attribute is added only if the isolation cell output is not inverted to indicate that the enable driver supply must be on when the cell is in the partial power down state.The permit_power_down attribute is added only if the isolation cell output is not inverted. This attribute is added on the power pin for a NOR isolation cell and on the ground pin for a NAND isolation cell to indicate that the related supply can be off while in isolation mode.
  • When the value of updateRelatedSuppliesForNorNandIsoPorts = nil (default).
    • No changes are done in the related_power_pin or related_ground_pin attribute values. The alive_during_partial_power_down attribute is added only if the isolation cell output is not inverted to indicate that the enable driver supply must be ON when the cell is in the partial power down state. The permit_power_down attribute is added to the related power or ground pg_pin only if the isolation cell output is not inverted.
• Output ports connected to NOR/NAND isolation cell output pin
  • When the value of updateRelatedSuppliesForNorNandIsoPorts = t.
    • If the isolation enable immediate driver is not a macro input port, the related power pin or related ground pin values are updated based on the supply of the driver of the isolation cell enable pin.
    • The isolation_data_power_pin and isolation_data_ground_pin attributes are added to indicate related power/ground for a data driver inside a megacell.
    • If the isolation enable immediate driver is a macro input port, no changes are required in the related_power_pin or related_ground_pin attribute values. The alive_during_partial_power_down attribute is added to the output pin if the NOR/NAND isolation cell is without an inverted output. The permit_power_down attribute is added on the power pg pin of a NOR isolation cell or ground pg pin of a NAND isolation cell. The isolation_data_power_pin and isolation_data_ground_pin attributes are added to indicate the supply of the isolation cell data pin. A warning message is issued that the isolation enable signal is not buffered and is a direct connection to a macro port.
  • When the value of updateRelatedSuppliesForNorNandIsoPorts = nil (default).
    • No changes are made to the related_power_pin or related_ground_pin attribute values. The alive_during_partial_power_down attribute is added only if the NOR/NAND isolation cell is without an inverted output. The permit_power_down attribute is added only if the isolation cell is without an inverted output. This attribute is added on the power pg pin of a NOR isolation cell or ground pg pin of a NAND isolation cell.
    • The isolation_data_power_pin and isolation_data_ground_pin attributes are added to indicate related power/ground for a data driver inside a megacell.
    • If the isolation enable immediate driver is not a macro input port, the power_down_function attribute is updated to include clamp driver supplies and the isolation_enable_condition attribute.
    • If the isolation enable immediate driver is a macro input port, the power_down_function attribute is updated to include a macro input port connected enable pin. The alive_during_partial_power_down is set true on the macro port connected to an enable pin. A warning message is issued that the isolation enable signal is not buffered and is a direct connection to a macro port.

Related Topics

printAliveAndPermitAttributesinDotlib

updateRelatedSuppliesForNorNandIsoPorts

Extracting the Power Intent from a Design

Creation of Power Domains

Exporting 1801 Design Model

Exporting Liberty Power Model

Exporting Liberty Power Model

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