UPF Fundamentals – Power State Tables

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UPF Fundamentals – Power State Tables

Power State Table (PST) concept

Defining your power intent Power State Table (PST)

• Once you know more about what you are trying to define, specify the design switching characteristics in a power state table
• Requires knowing (or deciding) the operational voltages for each power domain, and the supplies being used.
  • Must know each voltage for each supply net, in each mode
  • UPF uses power state tables (PST) to define the relationship between these domains’ operational voltages
    • Defines all legal voltage states and power state combinations for a design
    • Captures dynamic voltage scaling (DVS/DVFS) and shutdown scenarios.

How Many States are needed?

• Mush define a state for each valid combination of supply values.  
  • –Example: Given 5 power domains
    • Each domain with at least one supply
    • Each supply with at least one value…

 

Power State Table

	Top	Orange	Green	Purple	Blue
FullOn	0.8V	1.0V	0.8V	0.8V	0.8V
LowPower	0.8V	1.0V	0.8V	0.6V	0.8V
LowerPower	0.8V	1.0V	0.6V	0.6V	0.6V

 

How Many States are needed?

• Shutdown quickly expands PST
  • Must represent both switched and unswitched supply nets in PST
  • Each shutdown supply will have at least two values
  • If all shutdown supplies operate independently, even more states must be defined.

 

 

Power State Table

	Top	Orange	Green pre-switch	Purple pre-switch	Blue pre-switch	Green	Purple	Blue
FullOn	0.8V	1.0V	0.8V	0.8V	0.8V	0.8V	0.8V	0.8V
LowPwr	0.8V	1.0V	0.8V	0.6V	0.8V	0.8V	0.6V	0.8V
LowerPwr	0.8V	1.0V	0.6V	0.6V	0.6V	0.6V	0.6V	0.6V
PwrSave	0.8V	1.0V	0.6V	0.6V	0.6V	0.6V	0.6V	OFF
Hibernate	0.8V	1.0V	0.6V	0.6V	0.6V	OFF	OFF	OFF

 

 

 

Is “Always-on” Really Always on?

• For a given shutdown power domain, cells in that domain remaining powered up during shutdown are referred to as “Always-ON” (AO)
  • Even if that “always-on” supply is also switchable
  • Hence the concept of “relative always-on”
    • An object that is powered up more than another is considered “always-on” from the perspective of that other object, regardless of whether it, too, can be shutdown.

 

 

PST

	TOP	PD1	PD2
ON	0.8V	0.8V	0.8V
LP	0.8V	0.8V	OFF
Sleep	0.8V	OFF	OFF

• PD1 is always-on, relative to PD2
• TOP is always-on, relative to PD2 and PD1.

 

Defining PST using supply Nets

Power State Table Commands

• add_port_state <port_name>

               {-state {name <nom> |<min nom max> |<off>}}

   --Defines all possible state information for a supply port

• create_pst <table-name> -supplieds {list}

   --Create “header” of a PST, using a specific ordered list of supply nets.

• add_pst_state <state_name>

               -pst <table-name> -state <supply_states>

--Defines valid combination of supply net values for each possible state of the design

Power State Table – Example

 

• Two power domains: TOP, pd1
• Four supplies, with these possible values
  • VDD                      1.08V
  • VDD_PD1             1.08V, 0.7V
  • VDD_PD1S           1.08V, 0.7V, OFF
  • VSS                        0.0V

Power State Table

 

There are the allowed combinations of supply values

 

 

 

PST Commands – Usage Tips

• You can use multiple add_port_state commands for the same port_name, as long as you are using different state identifier names

 

• You cannot use multiple add_pst_state commands using the same state_name

 

Wildcards are allowed for “don’t_care” state values in the PST

 

Power State Tables in Hierarchical Flow

• For the UPF, typically only one PST is defined, at the top level
• Hierarchical UPF methodology generally has PST’s being defined at the child level as well
• Notes when using Hierarchical UPF:
  • Supply ports which are connected in hierarchy with connect_supply_net should have the same power state names and values defined, for error propagation to the top level
  • Derived power states for which a design is checked against may not be the same as the power states defined at the top level
    • Review UPF-505 warnings generated during synthesis, for ignored or partially ignored power states.

 

Defining PST using supply Sets

Power State Definition with Supply Sets

• Defining power states tables with supply nets and supply ports
  • Use the add_port_state, create_pst, and add_pst_state commands to create the PST
  • Defining power states with supply sets
    • Define state information for a supply set by specifying the state of a specific supply function in the supply set
    • UPF command is add_power_state instead of add_port_state
    • NOTE: Supply sets mush have already been defined prior to using add_power_state
      • Using the create_supply_set command

 

add_power_state –Command Syntax

add_power_state<object_name> -state state_name

               [-supply_expr {boolean_function}]

               [-logic_expr {boolen_function}]

               [-simstate simstate]

               Where “boolean_function” is a System Verilog Boolean expression, not tcl

• For Synopsys today, the following requirements apply:
  • object_name must be a supply set name
  • Only one state can be added at a time for each add_power_state command
  • Only one supply set function can be referenced for each add_power_state command
  • Each sate_name and supply voltage must be unique for the supply set function being defined
    • Although the state_name can be reused in defining another supply set function

What is a Supply Net State?

• IEEE 1801 specification defines power state of a supply net to be one of the following:

Supply Net/Port State	Semantic
OFF	Supply net/port is electrically OFF. All elements driven by it will be corrupted.
FULL_ON	Supply net/port is connected to a supply-drive (e.g. VRM) which is fully ON
PARTICAL_ON	Supply net/port is connected to multiple power switches all of which are not FULL_ON
UNDETERMINED	Supply net/port has no connected path to a supply-drive

• These states are used in defining power state of a supply set function, using –supply_expr argument in the add_power_state command.

add_power_state –supply_expr

• The –supply_expr argument is used for defining the power behavior of supply nets and supply ports of a given supply set, for the power state being defined.
• For Synopsys today, this argument has the following syntax:

supply_set_function == function_state

• Where supply_set_function can be power of ground, and function_state can be one of the following:

`{status}

`{status, nom}

`{status, min, max}

`{status, min, nom, max}

• Status can be OFF or FULL_ON
• Min, nom, max are floating point numbers representing the min/nom/max voltages, respectively, of the specified state
• If status is FULL_ON, then at least one voltage must be specified

add_power_state –logic_expr

• The –logic_expr argument dictates when a particular state is TRUE; it is used for defining the behavior of supply sets, in terms of logic nets and supply nets
  • Boolean expression evaluates to TRUE when the object_name is the state being defined
  • Simple example: series of equality/inequality subexpressions of supply set (or power domain)  comparisons to state names –logic_expr {core_pd == turbo && ram_pd != sleep}
  • But can also be more complex expressions, to include logic events such as clock gating or frequency constraints in defining power state
  • For synopsis today, this arguments is ignored in implementation tools and is used only by verification tools
    • Used by simulation to determine in what state a domain exists, at a given time in simulation.

 

 

 

 

 

 

 

add_power_state –UPF Example

 

 

NOTE: Example assumes flat (single-scope) mode for all supply sets to be available globally.

• Two power domains: TOP, pd1
• Four supply nets, with these possible values
  • VDD                      1.08V
  • VDD_PD1             1.08V, 0.7V
  • VDD_PD1S           1.08V, 0.7V, OFF
  • VSS                        0.0V
  • Three supply sets:
    • ssTOP – primary supply set for the TOP domain, where
      • ssTOP.power == VDD
      • ssTOP.ground == VSS
• ssPD1 – primary supply set for the pd1 domain, where
  • ssPD1.power == VDD_PD1S
  • ssPD1.ground == VSS
• ssPD1_unswitched –always-on supply set, used for ISO, RR, etc.
  • ssPD1_unswithed.power == VDD_PD1
  • ssPD1_unswitchd.ground == VSS

 

 

 

Is a PST Still Needed when Using Supply Sets?

• add_power_state defines the state of a supply
  • PST defines the relationship between supplies’ states
  • Without a PST, the full cross-product of all supplies states will be assumed in implementation
    • If this is the desired implementation, a PST is not necessary, but tool performance will be significantly slower
    • Current recommendation is to continue using PST’s in designs using supply sets
      • Can use supply nets and ports for the PST commands, or can use supply set handles (<supply_set_name.function>)