Wireless Intel SpeedStep Power Manager

More documents

Recommendations

Info

White PaperWireless Intel SpeedStep ® Power ManagerRead PMUEventsCalculatethe StatisticDeterminethe StateInterfacewith PMPower Manager Idle ProfilerFigure 9. Performance ProfilerThe PMU tracks processor events as described in Table 2. ThePerformance Profiler also monitors the status registers ofperipheral devices such as the Intel PXA27x processor’s LCDController. This monitoring allows the Performance Profiler todynamically characterize the system state.8.0 Policy ManagerThe Policy Manager defines power states and maps them topower modes of the Intel PXA27x processor and/or WirelessIntel Communications Processor. If a power state is native tothe operating system, the Policy Manager uses the nativepower state and the operating system’s interface to the DPIsto transition the system into the specified power state. If thepower state is not native to the operating system, the PolicyManager creates the power state and uses the DPIs totransition the system into the specified power state.The Policy Manager uses device driver inputs, applicationworkload inputs (optional), Idle Profiler inputs, and PerformanceProfiler (system workload) inputs to define the system’s powerpolicy. Alternatively, an OEM can use these inputs to define itsown power policy.The Power Manager software provides an infrastructure to thedevice drivers for state changes, frequency changes, and voltagechanges. Using this infrastructure, the Power Manager softwarenotifies the client drivers of these changes either directly orthrough the operating system’s power management services.A system that is enabled by the Power Manager software willalways maintain a predefined operating point as part of a globalvariable, namely IPMOperatingPoint = [State, Voltage, Frequency,Frequency2, Frequency3]Information SourcePMU RegistersDescription of EventInstruction cache-missInstruction cache cannot deliverinstructionData dependency stallInstruction TLB missData TLB missInstruction executedNumber of Stalls an number of times thestall occurs due to D-Cache buffer full(every cycle condition is present)Data cache accessData cache-missData cache write-backSoftware changed the PCUsage for CharacterizationInstruction traffic and CPI estimation andcache locality%Memory usePage locality%CPU UsedData traffic / Data access congestion /Congestion rate and congestion lengthsData access rate, memory bound,%Memory useData traffic and %Memory useData trafficNumber of function callsTable 2. Intel ® PXA27x Processor’s Performance Monitoring Unit (PMU)12
Wireless Intel SpeedStep ® Power ManagerWhite PaperWhere:■■■■■State = Processor StateVoltage = Processor Core VoltageFrequency1 = Processor Core FrequencyFrequency2 = System Bus FrequencyFrequency3 = SDCLK FrequencyFor example, the state of the Intel PXA27x processor could beRun, Sleep, Standby, Idle, or Deep Idle.Similarly, the voltage and frequency can take on any of the valuessupported by the Intel PXA27x processor. At any given instant,the output of the Policy Manager sets IPMOperatingPoint to theoptimum values that achieve the required performance at thelowest power dissipation.9.0 Device Drivers Interface9.1 OverviewThe Power Manager software’s Device Interface Layer workswith the device drivers and the Power Manager software’sPolicy Manager as shown in Figure 10.Since many operating systems have some level of native powermanagement infrastructure, the Power Manager softwareinterfaces with this native infrastructure wherever possible. If theoperating system does not have a native power managementinfrastructure, the Power Manager software adds managementinfrasturcture. The Power Manager software ports the DriverInterface Layer of each operating system, providing a level ofabstraction that allows the Policy Manager to be decoupledfrom direct driver interaction.The following sections describe the generic architecture ofDriver interaction. The implementation details differ over variousoperating systems, and are addressed in separate OS-specificdocumentation.9.2 RegistrationThe Power Manager software has the ability to notify driverswhen power parameters change. This notification allows adriver to prepare for the pending transition, or to veto thetransition if necessary. During registration, the driver mustsupply a callback function either to the existing infrastructure ordirectly to the Power Manager software if no such infrastructureexists. The driver also must inform the Power Manager softwareof the target device's frequency and state sensitivity so that thePower Manager software will only notify the driver of a pendingstate transition when applicable.9.3 Device Driver Interface LayerBased on the implicit direction of flow, there are two categoriesof Driver interface types:■■Power Manager software-to-Driver interface: Thisinterface defines a set of routines that provide inputs to agiven registered driver. These routines allow the PowerManager software to notify a registered driver of its intentionto alter the system power state in some way, such as enteringStandby mode or Idle mode. Drivers must be able to vetothe Power Manager software's request to perform a powerparameter transition if doing so causes undesirable behavior.Driver-to-Power Manager software interface: Thisinterface defines a set of routines that a registered driver canuse to provide unique information regarding the targetdevice’s loading and power state to the Power Managersoftware. This information can help the Power Managersoftware make informed decisions in determining the optimalsystem power state. At a minimum, a registered driver mightonly provide a stub for these routines.Power Manager Policy ManagerPower Manager Device Driver Interface LayerOS Power Management InfrastructureDriver[0]Driver[1]Driver[1]Driver[n-1]Figure 10. Device Drivers Interface, Power Manager Software13
Page 6 and 7: White PaperWireless Intel SpeedStep
Page 16: White PaperWireless Intel SpeedStep

Wireless Intel SpeedStep Power Manager

Create successful ePaper yourself

Delete template?

Save as template?