Terminology
Design Objects
Design objects are objects named in the description of the design which can be in the form of RTL files or a netlist. Design objects can be referenced by the CPF commands.
Design
Followpins
Routing structures in the standard cells that allow routing of power and ground nets in a standard cell row through abutting of cells. Because the power and ground pins in the cells are aligned, the power and ground routing "follows the pins."
Instance
An instantiation of a module or library cell.
Hierarchical instances are instantiations of modules.
Leaf instances are instantiations of library cells.
Module
Net
A connection between instance pins and ports.
A logical net is a connection between pins or ports in the same module.
A logical net segment is a connection between one driver and one load within the same module.
A logical net with multiple fanouts has multiple (logical) net segments.A physical net is a connection between an leaf-level driver and one or more leaf-level loads.
All logical nets that are electrically connected make up one physical net.Note: In this document net refers to logical net.
Pad
An instance of an I/O cell, also referred to as a pad cell. The cell typically has one or more pins that must be connected to the package pins of a chip. Such pins are referred to as pad pins or pad ports.
Pin
An entry point to or exit point from an instance or library cell.
Port
An entry point to or exit point from the design or a module.
CPF Objects
CPF objects are objects that are being defined (named) in the CPF constraint file. CPF objects can be referenced by the CPF commands.
Analysis View
A view that associates an operating corner (or another lower-level analysis view in a hierarchical flow) with a power mode for which timing constraints were specified.
The set of active views represent the different design variations (MMMC, that is, multi-mode multi-corner) that will be timed and optimized.
Base and Derived Power Domains
A power domain whose primary power supply provides power to another power domain through a power switch network is called a base domain.
A power domain that derives its power from another power domain through a power switch network is called the derived domain.
Power domains can have multiple base domains.
A power domain can be a base domain and be a derived power domain from another power domain.
Isolation Rule
Defines the location and type of isolation logic to be added and the condition for when to enable the logic.
Level Shifter Rule
Defines the location and type of level shifter logic to be added.
Library Group
A list of libraries characterized for two or more operating conditions. All libraries in a group must have the same cells. A library group can be used in a DVFS design to interpolate power or timing data for any operating conditions.
Library Set
A set (collection) of libraries or library groups. By giving the set a name it is easy to reference the set when defining nominal conditions or operating corners.
The same library set can be referenced multiple times by different operating corners.
Mode
A static state of a design that performs one or more intended design functions. Typically, it is determined by the states of memory elements, states of power domains, and signal values.
Mode Transition
Defines when the design transitions between the specified power modes.
Nominal Operating Condition
A typical operating condition under which the design or blocks perform. An operating condition is determined by the voltages of all power supplies applied to a power domain, including the power voltage, ground voltage and the body bias voltage for PMOS and NMOS transistors. Depending on the technology used, this set of voltages determines whether the state of a power domain is on, off or in standby mode.
Operating Corner
A specific set of process, voltage, and temperature values under which the design must be able to perform.
Power Design
A unique power structure that can be associated with either a top design, or with one or more logic modules.
When a power design is associated with multiple logic modules, it allows the same power intent specification to be applied to instances of different modules.
On the other hand, a single logic module can have multiple power designs associated with it, allowing different power intent specifications to be applied to instances of a single design entity.
Power Domain
A collection of instances, pins and ports that can share the same power distribution network.
At the physical level a power domain contains
A set of power supply nets including a single pair of primary power and ground nets and optionally bias power and/or ground nets.
A set of cells with a single power and a single ground rail connecting to the primary power and ground nets
A set of special gates such as level shifter cells, state retention cells, isolation cells, power switches, always-on cells, or multi-rail hard macros (such as, I/Os, memories, and so on) with multiple power and ground rails
Note: Two or more power domains can have the same set of power and ground nets.
At the logic level a power domain contains
A set of logic gates that correspond to the (regular) physical gates of this power domain
A set of special gates such as level shifter cells, state retention cells, isolation cells, power switches, always-on cells, or multi-rail hard macros (such as, I/Os, memories, and so on) that correspond to the physical implementation of these gates in this power domain
At the RTL level a power domain contains
The computational elements (operators, process, function and conditional statements) that correspond to the logic gates in this power domain
Note: See also Base and Derived Power Domains and Secondary Power Domain.
Power Mode
A static state of a design in which each power domain operates at a specific nominal condition.
Power Mode Control Group
A set of power domains with an associated set of power modes and mode transitions that apply to this group only. A power mode group can contain other power mode groups.
Power Source Domain
A power domain that models the power source for the primary supply or the body bias supply of other domains.
Power Switch Rule
Defines the location and type of power switches to be added and the condition for when to enable the power switch.
Secondary Power Domain
A power domain
Xis a secondary power domain of a special low power instance if the primary power supply of domainXprovides the power supply to the non-switchable (secondary) power and (or) ground pins of the instance.
State Retention Rule
Defines the registers or regular flip-flop and latch instances to be replaced with state retention flip-flops and latches and the conditions for when to save and restore their states.
Virtual Port
A port that does not exist in the definition of a module before implementation, but that will be needed for the control signals of the low power logic such as isolation logic, state-retention logic, and so on. After implementation, these ports are added to the module definition in the netlist.
Virtual Power Domain
Power domain without instances and with no power and ground nets defined.
Special Library Cells for Power Management
Always On Cell
A special cell located in a switched-off domain that has secondary power or ground pins in addition to the primary power and ground pins. As long as the power supply to the secondary power or ground pins is on, the cell function does not change.
A special case of a global cell.
Global Cell
A special cell that has secondary power or ground pins in addition to the primary power and ground pins (followpins). In some cell designs, when the primary power or ground are switched off, the cell function can be different from the normal function when the primary power and ground are on. Also, in some cases, the cell can also have isolation logic built in at the cell input pins.
Examples of global cells are traditional always-on cells and other special low-power cells such as state retention cells and dual-rail isolation cells.
Isolation Cell
Logic used to isolate signals between two power domains where one is switched on and one is switched off.
The most common usage of such cell is to isolate signals originating in a power domain that is being switched off, from the power domain that receives these signals and that remains switched on.
Level Shifter Cell
Logic to pass data signals between power domains operating at different voltages.
Power Clamp Cell
A special diode cell to clamp a signal to a particular voltage.
Power Switch Cell
Logic used to connect and disconnect the power supply from the gates in a power domain.
State Retention Cell
Special flop or latch used to retain the state of the cell when its primary power supply is shut off.
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