Definitions of terms related to power
A collection of instances that use the same power supply during normal operation and that can be switched on or off at the same time. You can also associate boundary ports with a power domain to indicate that the drivers for these ports belong to the same power domain. The only leaf instances allowed are IP blocks and I/O pads. A power domain can be nested within another power domain.
At the physical level a power domain contains:
• A set of (regular) physical gates with a single power and a single ground rail connecting to the same pair of power and ground nets
• The nets driven by these physical gates
• 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. At least one pair of the power or ground rails in these special gates or macros must be connecting to the same pair of power and ground nets as the (regular) physical gates connect to.
At the logic level a power domain contains:
• A set of logic gates that correspond to the (regular) physical gates of this power domain
• The nets driven by these logic gates
• 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 RTL a power domain contains:
• The computational elements (operators, process, function and conditional statements) that correspond to the logic gates in this power domain
• The signals that correspond to the nets driven by the corresponding logic gates.
A static state of a design in which each power domain operates on a specific nominal condition.
The time from when the device decides to power off until the device is actually powered off.
The time taken until the device is actually shut off.
The time from when the device decides to power up until it is actually operational.
A special device located in a switched-off domain, and whose power supply is continuous on even when the power supply for the rest of the logic in the power domain is off.
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.
Logic to pass data signals between power domains operating at different voltages.
A special diode cell to clamp a signal to a particular voltage.
Logic used to connect and disconnect the power supply from the gates in a power domain.
Special flop or latch used to retain the state of the cell when its main power supply is shut off.
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