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<concept id="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703" xml:lang="en"><title>Power

Controller DPowerController Implementation Tutorial</title><shortdesc>This topic describes how to implement the <codeph>DPowerController</codeph> class

to provide the main power controller functionality in a base port.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p><xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita"><apiname>DPowerController</apiname></xref> is defined as: </p>

<codeblock id="GUID-95318C39-B205-557C-B1F3-75C1441E464A" xml:space="preserve">class DPowerController : public DBase

    {

public:

    IMPORT_C DPowerController();

    IMPORT_C void Register();

    IMPORT_C void WakeupEvent();

#ifndef __X86__

    IMPORT_C TInt RegisterResourceController(DBase* aController, TInt aClientId);

private:

    struct SResourceControllerData

        {

        DBase* iResourceController;

        TInt   iClientId;

        } iResourceControllerData;

#endif

public:

    volatile TPowerState    iTargetState;

public:

    virtual void CpuIdle() = 0;

    virtual void EnableWakeupEvents() = 0;

    virtual void DisableWakeupEvents() = 0;

    virtual void AbsoluteTimerExpired() = 0;

    virtual void PowerDown(TTimeK aWakeupTime) = 0;

    };

      </codeblock>

<p>The first three functions are exported from the kernel, <filepath>EKERN.EXE</filepath>,

while the other five pure virtual functions are implemented by your base port.

You do not need to export any other functions. </p>

<ul>

<li id="GUID-2EEFEFF3-FCAF-526C-A11B-790A2A47AA9C"><p> <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-BCCDBA09-415D-5779-BCE5-CDEB2E1EF7D8">Initialising the power controller</xref>, </p> </li>

<li id="GUID-CBB1EE9C-CD27-5417-973C-3BBED74715D6"><p> <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-DCD91EBA-CB0E-5EA9-84E0-8F8FED6FC91E">DPowerController::RegisterResourceController()</xref>, </p> </li>

<li id="GUID-4E2D396D-E6FA-5658-830F-9F82D4A63AD1"><p> <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-5A0CAD08-AA12-56EE-B0A3-75548D1896C9">DPowerController::EnableWakeupEvents()</xref>, </p> </li>

<li id="GUID-DB82BCE3-702A-51EB-ADE0-9434D59CD553"><p> <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-51D37A0C-AD46-52D5-A31C-CB3A8046CE84">DPowerController::AbsoluteTimerExpired()</xref>, </p> </li>

<li id="GUID-77CCBFFE-037D-5B86-BF14-1BE87D38B47A"><p> <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-1F77C71C-D226-58BB-ABAE-43F958CC0C61">DPowerController::PowerDown()</xref>, </p> </li>

<li id="GUID-8657D772-2338-588D-B074-832B06144D8B"><p> <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-E2A072D0-A67F-5E6D-81ED-CFD77B6ED4F1">CpuIdle()</xref>. </p> </li>

</ul>

<section id="GUID-BCCDBA09-415D-5779-BCE5-CDEB2E1EF7D8"><title>Initialising

the power controller</title> <p>Typically, you implement your derived class

in a power management kernel extension, which has the opportunity to perform

initialisation before the system itself is fully initialised. This is done

via the extension's DLL entry point. You use the <xref href="GUID-7964FC46-4641-3BDD-92C9-50FA22C3321A.dita"><apiname>DECLARE_STANDARD_EXTENSION()</apiname></xref> macro

as a wrapper around your initialisation code. There are at least three things

to do here: </p> <ul>

<li id="GUID-25C66F1B-6B2F-5B3B-A827-410263EE22A4"><p>create an instance of

your power controller object </p> </li>

<li id="GUID-369A09EC-74D3-529A-AC05-0EFE0C4ABBF7"><p>register your power

controller object with the Symbian platform power manager, by calling <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-F66D72D0-AA27-3BAF-8915-C6E8CC4E7CCF"><apiname>DPowerController::Register()</apiname></xref>.

Your power controller cannot be used by the Symbian platform power manager

until it has been registered. </p> </li>

<li id="GUID-E4C7D934-AAB9-511B-93A4-125D5A5B248D"><p>if you intend to use

a battery monitor, then you would create it and register it as the HAL handler

to deal with <xref href="GUID-66A851A0-2A0C-3624-AEC1-22F6629FABF7.dita#GUID-66A851A0-2A0C-3624-AEC1-22F6629FABF7/GUID-227B4DCD-5D74-3AB7-8E09-64A04D88F094"><apiname>THalFunctionGroup::EHALGroupPower</apiname></xref> calls. See <xref href="GUID-65CDCA83-C726-5173-8E46-B8981D1D7B02.dita">Battery Monitor Implementation

Tutorialc</xref> and <xref href="GUID-54042C84-6216-5930-9CBF-BAF635CECD4D.dita">Power

HAL Handler Tutorial</xref> for more detail. </p> </li>

</ul> <p>For example: </p> <codeblock id="GUID-1A909C4C-DCAF-54E3-B482-16918E33BF4F" xml:space="preserve">DECLARE_STANDARD_EXTENSION()

    {

    TInt r=KErrNoMemory;

    // Create the power controller object, and register it.

    DPowerController* pC = new DYourPowerController;

    if !(pC)

        {

        return (r);

        }

        pC->Register();

    // Create the battery monitor.

    DBatteryMonitor* pM = new DYourBatteryMonitor;

    if !(pM)

        {

        return(r);

        }

    r = KErrNone;

    return(r);

    }</codeblock> </section>

<section id="GUID-DCD91EBA-CB0E-5EA9-84E0-8F8FED6FC91E"><title>DPowerController::RegisterResourceController()</title> <p>The

function <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-42896B4D-9F77-3D91-82BD-50102A8F3DA4"><apiname>DPowerController::RegisterResourceController()</apiname></xref> allows

the Resource Controller to register itself with the Power Controller. See <xref href="GUID-66FD040B-133E-57CF-80DD-9369F62709C6.dita#GUID-66FD040B-133E-57CF-80DD-9369F62709C6/GUID-08BFCAF4-9AF0-5999-A1C4-7BBD107C9354">registering

with the resource controller</xref> in the PSL implementation document. </p> <p>To

support idle power management the Power Controller's PSL must override <codeph>RegisterResourceController()</codeph> to

include the registration of a list of resources whose states are of interest

to idle power management. </p> <p><b>Idle

power management</b> </p> <p>The Power Controller can assemble a list of resources

whose state it is interested in from a NULL thread in an array of <xref href="GUID-586AF75A-8350-345D-ABF4-6542C8E75DED.dita"><apiname>SIdleResourceInfo</apiname></xref> structures.

Each entry in the list contains the resource ID that the power controller

must enter before registering with the PRM. The resource list should be created

in the kernel heap or data section. </p> <p>The example below creates a buffer

to capture the state of all static resources. The PRM captures the information

using <xref href="GUID-46F2174F-0206-345B-8C5D-F8B5763652E0.dita#GUID-46F2174F-0206-345B-8C5D-F8B5763652E0/GUID-52DC308A-9DF1-3BDE-A905-A4DD3B692638"><apiname>DPowerResourceController::RegisterResourcesForIdle()</apiname></xref>. </p> <codeblock id="GUID-C6E907FD-094D-5412-8F81-FC02CDE8B411" xml:space="preserve">    ...

//Allocate buffer for Idle resource management

    NKern::ThreadEnterCS();

    pBuf = HBuf::New(numResources * sizeof(SIdleResourceInfo)); 

    NKern::ThreadLeaveCS();

    if(!pBuf)

        {

           return KErrNoMemory;

        }

    SIdleResourceInfo* pI = (SIdleResourceInfo*)pBuf->Ptr();

//Update resource ID

    for(TUint c = 0; c < numResources; c++)

        {

        pI[c].iResourceId = c+1; 

        }

    r = (iResourceControllerData.iResourceController)->RegisterResourcesForIdle(iResourceControllerData.iClientId, numResources, (TPtr*)pI);

    ...</codeblock> <p>The first parameter passed to <codeph>RegisterResourcesForIdle()</codeph> is

the client Id generated for the power controller this is the client ID passed

by the PRM when calling <xref href="GUID-B2C466D1-0B65-3BB7-81B1-7297400E60C4.dita"><apiname>RegisterResourceController</apiname></xref>. </p> <p> <b>Note</b>: <codeph>RegisterResourcesForIdle()</codeph> is

not exported and is only available for use by the Power Controller to register

resources for idle power management. <b>Note</b>: <codeph>RegisterResourcesForIdle()</codeph> can

only be called by the Power Controller once. </p> </section>

<section id="GUID-5A0CAD08-AA12-56EE-B0A3-75548D1896C9"><title>DPowerController::EnableWakeupEvents()</title> <codeblock id="GUID-38714507-C38C-5787-997F-5D45F3A90357" xml:space="preserve">virtual void EnableWakeupEvents() = 0;</codeblock> <p>The

Symbian Power Model defines 3 generic system-wide <xref href="GUID-113B3755-1797-5D1B-8E07-8A18F5FE1504.dita">power

states</xref>: <i>Active</i>, <i>Standby</i> and <i>Off</i>, as defined in

the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita">Symbian platform

power model</xref>. </p> <p>Each of the system-wide low power states: <i>Standby</i> and <i>Off</i>,

has a defined set of wake-up events. If a wake-up event occurs while the system

is preparing to transition into one of these low power states, or when the

system is in the <i>Standby</i> state, then this can result in the system

moving back to the <i>Active</i> power state. Wake-up events may be different

for different target power states. Wake-up events are platform-specific hardware

events, and it is your base port that decides which events count as wake-up

events. </p> <p><b>When

is it called?</b> </p> <p> <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-0642129D-05F2-3AB0-B562-37A7BB7A275F"><apiname>DPowerController::EnableWakeupEvents()</apiname></xref> is

called called by the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-330F07B2-BBDF-5675-B7D5-FF6B25DD03F4">power

manager</xref> as a result of a user side call to <xref href="GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87.dita#GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87/GUID-C49C0A07-EAC7-32CB-956F-1FFEFF2FD326"><apiname>Power::EnableWakeupEvents()</apiname></xref>.

The class <xref href="GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87.dita"><apiname>Power</apiname></xref> is the user side interface to the power

manager, and is used by the user side entity that is responsible for moving

the device into a low power state. </p> <p><b>Context</b> </p> <p>When the user side entity decides to move the device to a low power

state, it sends a notification to all of the user side power domains registered

with it, giving their applications a chance to save their data and state.

However, before doing this, it calls <xref href="GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87.dita#GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87/GUID-C49C0A07-EAC7-32CB-956F-1FFEFF2FD326"><apiname>Power::EnableWakeupEvents()</apiname></xref>.

It also calls <xref href="GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87.dita#GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87/GUID-6CFE19D9-249A-3305-8224-823D2FDB1859"><apiname>Power::RequestWakeupEventNotification()</apiname></xref> so

that it can be informed of a wake-up event. If it is notified of a wake-up

event, it can halt, and reverse the user side response to the power transition. </p> <fig id="GUID-ACC6E7E3-71E3-5553-B433-9017CB04513D">

<image href="GUID-65F3E8BD-22C9-5CF2-A3CC-270C24ADECC0_d0e388259_href.png" placement="inline"/>

</fig> <p>Before calling <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-0642129D-05F2-3AB0-B562-37A7BB7A275F"><apiname>DPowerController::EnableWakeupEvents()</apiname></xref>,

the power manager sets the <codeph>iTargetState</codeph> member of <codeph>DPowerController</codeph> to

the applicable <xref href="GUID-87AB8B20-04EE-31D2-8F3D-EA904D05B8D0.dita"><apiname>TPowerState</apiname></xref>. This means that you can enable

the appropriate set of wake-up events. </p> <p>Once the user side transition

is complete, it calls <xref href="GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87.dita#GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87/GUID-7C6F3F0F-319B-3DEE-81BF-1EB5BB2EAB0A"><apiname>Power::PowerDown()</apiname></xref> in the user side

interface to the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-330F07B2-BBDF-5675-B7D5-FF6B25DD03F4">power

manager</xref>, which results in a call to <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-8AE99718-6B82-3920-9029-28C2041A3B10"><apiname>DPowerController::PowerDown()</apiname></xref> in

the power controller. This starts the transition of all <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-DC5F1ECD-CCA3-59FF-A2F1-A3DBD76CD458">power handlers</xref> to a low power state, a potentially long process. This

means that the power controller needs the ability to detect wake-up events

so that it can halt, and reverse the power transition. </p> <p><b>Implementation issues</b> </p> <p>There are three possibilities in dealing

with wake-up events: </p> <ul>

<li id="GUID-4243E6DD-C903-58DE-B125-38CEDB8B5269"><p>if wake-up events are

not handled by specific peripheral drivers, you could set up the hardware

so that wake-up events are recorded in a location accessible by the software.

Prior to completing the system power transition, the Power controller would

check the relevant hardware to see whether a wakeup event had occurred. On

detecting a wake-up event it would tell the power manager by calling <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-C193F898-2C15-3C42-8353-14F00789BCDA"><apiname>DPowerController::WakeupEvent()</apiname></xref>. </p> </li>

<li id="GUID-289B86C4-A578-5A42-A0DF-70A7BF3F440E"><p>if wake-up events are

not handled by specific peripheral drivers, you could arrange for wake-up

events to interrupt the CPU. The code that services those interrupts would

tell the power manager by calling <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-FABDB7E2-DEC5-3EA9-8106-66C971C04AB7"><apiname>DPowerController::WakepEvent()</apiname></xref>. </p> </li>

<li id="GUID-E51BAE55-0A81-5D1F-B509-096A7F2141EF"><p>if wakeup events are

intercepted, serviced and cleared by peripheral drivers, then the following

outline solution could be adopted: </p> <ul>

<li id="GUID-5C942237-BBB2-5919-8578-B55BDAFAFC9F"><p>The power controller

would need to publish a list of wake-up events, preferably as a bit mask,

and export an API which peripheral drivers could use to notify the power controller

that a wake-up event has occurred. The following interface class could be

used for this purpose: </p> <codeblock id="GUID-084F7F46-66B6-5661-85AF-57D499250886" xml:space="preserve">class TPowerController

    {

public:

    inline static void SetPowerControllerPointer(DPowerController* apPowerController)

    { iPowerControllerPointer = apPowerController; }

    IMPORT_C static void WakeupEventOccurred(TUint aWakeupEvent);

    …        // other methods if required

private:

    DPowerController* iPowerControllerPointer;

    };

                      </codeblock> <p>The class would be implemented as part

of the power management kernel extension and <codeph>SetPowerControllerPointer()</codeph> would

be called when <xref href="GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703.dita#GUID-34D1D0BF-20DE-5677-A067-8FF9DD72E703/GUID-BCCDBA09-415D-5779-BCE5-CDEB2E1EF7D8">initialising

the power controller</xref>, but after creation of the power controller object. </p> <p>Those

peripheral drivers that intercept wake-up events would need to link to the

power controller DLL (i.e. the power management kernel extension). </p> <p>On

the occurrence of a wake-up event, the peripheral driver software servicing

that event would notify the power controller by calling <codeph>WakeupEventOccurred()</codeph>,

specifying the appropriate wake-up event bit(s). </p> <p>You might implement <codeph>WakeupEventOccurred()</codeph> as

follows: </p> <codeblock id="GUID-501ABA28-81B9-52C1-9842-003E1E389045" xml:space="preserve">EXPORT_C void TPowerController::WakeupEventOccurred(TUint aWakeupEvent)

    {

    if(iPowerControllerPointer->iWakeupEvents & aWakeupEvent)

        {

        iPowerControllerPointer->WakeupEvent();

        }

    }</codeblock> <p>where <codeph>iWakeupEvents</codeph> is a data member

defined in your <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita"><apiname>DPowerController</apiname></xref> -derived class that contains

the bitmask representing the wake-up events. The bitmask groups wakeup events

according to the target power state. </p> </li>

</ul> </li>

</ul> <p>When the peripheral driver powers down, it should leave the hardware

that generates the wake-up event powered and enabled for detection. Thus,

if a wake-up event of the type handled by this peripheral driver occurs, it

will not be serviced in the normal way, but will be left pending until the

power controller services it. </p> <p>When the power controller’s <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-8AE99718-6B82-3920-9029-28C2041A3B10"><apiname>DPowerController::PowerDown()</apiname></xref> function

is called, the power controller must check the peripheral hardware directly

to see whether the wakeup event has happened, or is happening right now, prior

to transitioning the device to the target system-wide low power state. If

the wake-up event is found to have happened then <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-8AE99718-6B82-3920-9029-28C2041A3B10"><apiname>DPowerController::PowerDown()</apiname></xref> would

return immediately, instead of initiating the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-DC5F1ECD-CCA3-59FF-A2F1-A3DBD76CD458">power

handlers</xref> power down of the peripheral drivers. </p> </section>

<section id="GUID-51D37A0C-AD46-52D5-A31C-CB3A8046CE84"><title> DPowerController::AbsoluteTimerExpired()</title> <codeblock id="GUID-5EC61B73-DA37-51C8-963F-4E4169AC1BE7" xml:space="preserve">virtual void AbsoluteTimerExpired() = 0;</codeblock> <p><b>When is it called?</b> </p> <p> <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-C6F792DB-1EC0-33F4-8F82-AB3F7B44B061"><apiname>DPowerController::AbsoluteTimerExpired()</apiname></xref> is

called by the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-330F07B2-BBDF-5675-B7D5-FF6B25DD03F4">power

manager</xref> whenever an absolute timer expires. An absolute timer is one

that is set to complete at a specific time, as queued by a call to <xref href="GUID-8A423EA2-4264-30C9-9579-0466994E6E88.dita#GUID-8A423EA2-4264-30C9-9579-0466994E6E88/GUID-3F302410-5CC2-3CCB-82F4-47E953E7A29B"><apiname>RTimer::At()</apiname></xref>. </p> <p><b>Implementation issues</b> </p> <p>If absolute timer expiration is one

of your wake-up events, then your implementation of <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-C6F792DB-1EC0-33F4-8F82-AB3F7B44B061"><apiname>DPowerController::AbsoluteTimerExpired()</apiname></xref> should

call <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-C193F898-2C15-3C42-8353-14F00789BCDA"><apiname>DPowerController::WakeupEvent()</apiname></xref> to notify the power

manager that a wake-up event has happened. </p> <p>It is recommended that

you track absolute timers. </p> </section>

<section id="GUID-1F77C71C-D226-58BB-ABAE-43F958CC0C61"><title>DPowerController::PowerDown()</title> <codeblock id="GUID-AD394AD5-8E3E-5FE3-938E-639C4E5E9F79" xml:space="preserve">virtual void PowerDown(TTimeK aWakeupTime) = 0;</codeblock> <p><b>When is it called?</b> </p> <p> <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-8AE99718-6B82-3920-9029-28C2041A3B10"><apiname>DPowerController::PowerDown()</apiname></xref> is

called by the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-330F07B2-BBDF-5675-B7D5-FF6B25DD03F4">power

manager</xref> to move the device into one of the system-wide low power states: <i>Standby</i> or <i>Off</i>. </p> <p>Typically,

this is a result of the user side entity that is responsible for moving the

device into a low power state calling <xref href="GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87.dita#GUID-15D25C07-CFD2-32CE-AD22-E17D512D8E87/GUID-7C6F3F0F-319B-3DEE-81BF-1EB5BB2EAB0A"><apiname>Power::PowerDown()</apiname></xref> in

the user side interface to the <xref href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita#GUID-0C435514-EEC6-5660-BB5F-535790349632/GUID-330F07B2-BBDF-5675-B7D5-FF6B25DD03F4">power

manager</xref>. </p> <p>If <xref href="GUID-26621CA5-B686-53FB-AF3E-96CDD38C8520.dita">physical

RAM defragmentation</xref> is implemented you may wish to include calls to <xref href="GUID-AE7E0A8E-1513-3F6B-A6D5-150084C4E262.dita#GUID-AE7E0A8E-1513-3F6B-A6D5-150084C4E262/GUID-B4825007-E3DB-3559-9D58-637150EF3DB9"><apiname> TRamDefragRequest::DefragRam()</apiname></xref> within

this function to enable defragmentation of RAM zones that can then be powered

down. </p> <p><b>Context</b> </p> <p>The

target state is defined by the value of the <codeph>iTargetState</codeph> member

of <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita"><apiname>DPowerController</apiname></xref>, as set by the power manager. </p> <p><b>Implementation issues</b> </p> <p>Implementation depends on the target

state: </p> <ul>

<li id="GUID-0473B5C1-BEC0-5276-88C5-A4A8379A4621"><p>if the target state

is <i>Standby</i>, as implied by a value of <xref href="GUID-87AB8B20-04EE-31D2-8F3D-EA904D05B8D0.dita#GUID-87AB8B20-04EE-31D2-8F3D-EA904D05B8D0/GUID-5604F598-8CBC-3A94-865F-CA58DA4492B0"><apiname>TPowerState::EPwStandby</apiname></xref> in <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-86A0C14F-B219-3E0B-BD5E-A2C20EEDBF64"><apiname>DPowerController::iTargetState</apiname></xref>,

then the power controller should put the hardware into a state corresponding

to the <i>Standby</i> state. </p> <p>If at least one wake-up event has been

detected and recorded since the last call to <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-0642129D-05F2-3AB0-B562-37A7BB7A275F"><apiname>DPowerController::EnableWakeupEvents()</apiname></xref>,

then <codeph>PowerDown()</codeph> should return immediately; otherwise, it

should continue with the process of putting the device into <i>Standby</i>;

execution of the function will halt, and can only continue, and return, when

a wake-up event occurs. </p> </li>

<li id="GUID-E38B9334-CFE4-5E91-9DD4-D7A0678AF344"><p>if the target state

is <i>Off</i>, as implied by a value of <xref href="GUID-87AB8B20-04EE-31D2-8F3D-EA904D05B8D0.dita#GUID-87AB8B20-04EE-31D2-8F3D-EA904D05B8D0/GUID-0DAD6E93-BD08-3C90-BCE8-ADBFC2681227"><apiname>TPowerState::EPwOff</apiname></xref> in <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-86A0C14F-B219-3E0B-BD5E-A2C20EEDBF64"><apiname>DPowerController::iTargetState</apiname></xref>,

then <codeph>PowerDown()</codeph> must <i>never</i> return. Typically, the

power controller turns the device off, but can choose to perform other device-specific

action such as a system reboot. </p> </li>

</ul> <p>The <xref href="GUID-8C6E2996-24DE-3E59-927A-46D32290225E.dita"><apiname>TTimeK</apiname></xref> parameter passed to the function is

a system time value. If non-zero, it specifies the time when the system should

wakeup. The kernel calculates it as the time that the next absolute timer

expires. Typically, your implementation will use the Real Time Clock module

to generate an event at the specified time, and this will cause a return to

the <i>Active</i> state. This implies that the base port should enable Real

Time Clock event detection during <i>Standby</i>. </p> <p>The Symbian definition

of the <i>Standby</i> state usually translates into the hardware manufacturer’s

CPU “Standby” or “Sleep” modes of operation. Typically, the internal clocks

associated with the core and some of the core peripherals, or their power

supply, are suppressed, and their internal state is not preserved. In this

case, the state of the core and core peripherals should be saved before going

into <i>Standby</i> so that they can be restored when the system wakes-up.

Note the following: </p> <ul>

<li id="GUID-824D88FD-33FB-50DC-A904-F5F44BFBF90A"><p>for the core state,

save the current mode, the banked registers for each mode, and the stack pointer

for both the current mode and user mode </p> </li>

<li id="GUID-E8CDFA98-E6F2-5D48-987F-E2591DAB242B"><p>for the core peripherals,

save the state of the interrupt controller, the pin function controller, the

bus state controller, and the clock controller </p> </li>

<li id="GUID-90BEA663-F58C-5AD7-8578-353E5EFFBCCC"><p>for the MMU state, save

the control register, the translation table base address, and the domain access

control, if this is supported </p> </li>

<li id="GUID-68AB9558-5CC7-573F-8A33-A38F16EAF304"><p>flush the data cache

and drain the write buffer. </p> </li>

</ul> <p>If all of this data is saved to a DRAM device, then this should be

put into self refresh mode. </p> <p>Peripherals modules involved in the detection

of wake-up events should be left powered. </p> <p>Tick timer events should

be disabled, and the current count of this and any other system timers should

be saved; relevant wake-up events should be left unmasked, and any others

should be disabled. </p> </section>

<section id="GUID-E2A072D0-A67F-5E6D-81ED-CFD77B6ED4F1"><title>DPowerController::CpuIdle()</title> <codeblock id="GUID-0E6F1B1D-F979-575B-BA3C-096CE4C0CA15" xml:space="preserve">virtual void CpuIdle()=0;</codeblock> <p><b>When is it called?</b> </p> <p> <xref href="GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366.dita#GUID-B3D1C422-6A82-3C6E-9123-1E4F598F0366/GUID-473874CA-FC35-3EB2-BC23-A97D7176B833"><apiname>DPowerController::CpuIdle()</apiname></xref> is

called whenever the Null thread is scheduled to run. This can happen as soon

as the power model has been installed. It is the mechanism through which your

base port can increase power savings when the system becomes inactive by moving

the CPU or the system into a low power mode. </p> <p>If <xref href="GUID-26621CA5-B686-53FB-AF3E-96CDD38C8520.dita">physical

RAM defragmentation</xref> is implemented you may wish to include calls to <xref href="GUID-AE7E0A8E-1513-3F6B-A6D5-150084C4E262.dita#GUID-AE7E0A8E-1513-3F6B-A6D5-150084C4E262/GUID-B4825007-E3DB-3559-9D58-637150EF3DB9"><apiname> TRamDefragRequest::DefragRam()</apiname></xref> within

this function to enable defragmentation while the device is idle. </p> <p><b>Implementation issues</b> </p> <p>The implementation can call the Variant

or ASSP implementation of <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita#GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D/GUID-6F242C0C-2EFC-30EC-9A5E-A34C8D15E0D7"><apiname>Asic::Idle()</apiname></xref>. </p> <p>The idle

state is usually implemented via a Wait-For-Interrupt type instruction that

will usually suspend execution of the CPU, possibly triggering other ASIC

power saving actions, and will resume execution when any unmasked interrupt

occurs. </p> <p><b>Suppressing

the system tick interrupt</b> </p> <p>To further increase power savings during

CPU Idle, a base port can choose to suppress the system tick interrupt until

the next nanokernel Timer (as implemented by <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref>) is

due to expire. Nanokernel timers are the basic timing service and all Symbian

platform tick-based timers and time-of-day functions are derived from nanokernel

timers. </p> <p>In EKA2, timing services rely on a hardware timer, which is

programmed by the base port Variant code, to generate the system tick. We

refer to this as the <i>system timer</i>. </p> <p>Typically, the platform-specific

ASSP or Variant object has a pointer to the nanokernel timer queue, an <xref href="GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0.dita"><apiname>NTimerQ</apiname></xref> object.

The number of ticks before the next <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref> is due to expire

can be found by calling <xref href="GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0.dita#GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0/GUID-69103F26-2C21-3ECA-9DB5-C31A41F6C238"><apiname>NTimerQ::IdleTime()</apiname></xref>. </p> <p>Before

going into Idle mode, <codeph>CpuIdle()</codeph> disables the hardware timer

used to generate the system tick (i.e. the system timer) for the number of

ticks to be suppressed; i.e. the system timer is reset to go off and generate

an interrupt only when the <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref> expires. Note that the

clock supply to the hardware timer must be left enabled. </p> <p>On returning

from Idle mode, the software must examine the system timer and decide whether

the <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref> expiration was responsible for waking up the

processor, or whether it was due to some other interrupt. </p> <p>If waking

up was due to the <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref>, the system timer must be reset

to generate the system tick at the frequency desired, and the tick count, <xref href="GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0.dita#GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0/GUID-ACFDFE7C-19AE-3C81-9D38-3266A3A3EF1F"><apiname>NTimerQ::iMsCount</apiname></xref>,

must be adjusted with the <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref> expiration time. As the

expiration time is always an integer multiple of the number of ticks, then

the <xref href="GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0.dita#GUID-C54D99AA-FF6E-3023-8260-8F5A88FBFBE0/GUID-AA1EC86F-8A6E-340D-848F-A86554772A13"><apiname>NTimerQ::Advance()</apiname></xref> function can be used for this purpose. </p> <p>If

waking up was due to another interrupt, then the software must read the system

timer and calculate the time elapsed since going into Idle mode, and adjust

the system tick count with the elapsed time (which could be a fractional number

of ticks) and reprogram the system timer to continue generating the tick after

the correct interval, as above. </p> <p>If the hardware timer that is used

to generate the system ticks does not use a Compare-Match function, then some

care has to be taken not to introduce skewing when manipulating the timer

value directly. If the timer needs to be reloaded with the new value to give

the next tick, then the software usually “spins”, waiting for the hardware

timer to change, and then reloads it. This way the timer will always be reloaded

on an edge of its internal clock. </p> <p><b>Waking

up from “Sleep” modes with long wakeup latencies</b> </p> <p>Often, to further

enhance power savings, the CPU and some peripherals are moved into a hardware

“sleep” mode when <codeph>CpuIdle()</codeph> is called. This could be of long

latency, and waking up could take longer than the system Tick period. There

are two situations: </p> <ul>

<li id="GUID-7484F7CB-C824-5752-9043-736E95D4405D"><p>if the wakeup time can

be determined precisely, then <codeph>CpuIdle()</codeph> programs the system

timer to bring the CPU back from the “Sleep“ mode at a time corresponding

to the next <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref> expiration (as a number of Ticks to

suppress) <i>minus</i> the number of ticks it takes to wake up from that mode.

On waking up on the timer, the System tick count should be adjusted with the

total number of ticks suppressed, i.e. the count corresponding to the time

of the <xref href="GUID-D8CF05A3-5C9B-3662-92DA-3290C6EE7FD2.dita"><apiname>NTimer</apiname></xref> expiration. </p> </li>

<li id="GUID-C0A9B2A2-D98D-50C0-B58A-4E84FCEC12E4"><p>If the wakeup time cannot

be known deterministically, then the above scheme must be combined with another

system to allow adjusting the system timer from the hardware Real Time Clock

(RTC). </p> <p>Typically, the hardware RTC is clocked with a 1Hz clock, and

can be programmed to interrupt the CPU on multiples of one second intervals.

The clock supply to the RTC must be left enabled on going into "sleep" mode. </p> </li>

</ul> <p>To guarantee that timed events occur when they are due, the CPU should

only be allowed to go to into the long latency hardware “sleep” mode if the

RTC can be guaranteed to complete a second tick before the CPU is due to wakeup. </p> <p>Note

that if waking up from hardware “Sleep” mode takes a non-negligible amount

of time, extreme care should be taken when deciding to move the platform into

that mode. For example, if a receive request is pending on a data input device <i>and</i> the

CPU reaches the Idle mode <i>and</i> the platform is transitioned into a “sleep”

state <i>and</i> data arrives while it is still in that state, <i>then</i> there

is a possibility that the system will not wake up on time to service the incoming

data. </p> </section>

<section id="GUID-4B613C67-3A12-4AD5-8842-6ED510A68746"><title>Validation</title> <p>The <filepath>e32test</filepath> programs <filepath>t_power</filepath>, and <filepath>t_timer</filepath> will put the system into standby and resume

off a timer. </p> </section>

</conbody><related-links>

<link href="GUID-0C435514-EEC6-5660-BB5F-535790349632.dita"><linktext>Power Management</linktext>

</link>

</related-links></concept>