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<concept id="GUID-A789E0D6-74B2-517D-B73A-F9B11794F175" xml:lang="en"><title>Peripheral
Driver Power Implementation Tutorial</title><shortdesc/><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Peripheral driver power management is based on the <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref> class.
This is a class that defines the interface that the driver must provide to
the generic kernel side power manager. </p>
<p>The class also provides the necessary support functions. The class is defined
as: </p>
<codeblock id="GUID-C34B90B1-5AB2-51E4-A7C9-01601B8698F6" xml:space="preserve">class DPowerHandler : public DBase
    {
public:
    IMPORT_C ~DPowerHandler();
public:
    IMPORT_C DPowerHandler(const TDesC&amp; aName);
    IMPORT_C void Add();
    IMPORT_C void Remove();
    IMPORT_C void PowerUpDone();
    IMPORT_C void PowerDownDone();
    IMPORT_C void SetCurrentConsumption(TInt aCurrent);
    IMPORT_C void DeltaCurrentConsumption(TInt aCurrent);
public: 
    virtual void PowerDown(TPowerState aTargetState) = 0;
    virtual void PowerUp() = 0;
private:
    ...
    };
      </codeblock>
<p>Typically, at least one power handler object is implemented by the peripheral
driver. In some cases the peripheral driver interface class may derive from <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref>,
in others it creates and owns an instance of a <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref> derived
class. </p>
<p>The Symbian port of the <xref href="GUID-8C22AF20-EE0E-5AD2-BEFD-FED5A7DBB09B.dita">LCD
Extension</xref> for the Lubbock reference board is an example of the first
type of implementation. </p>
<p>The first eight functions are exported from the kernel, <filepath>EKERN.EXE</filepath>,
while the remaining two pure virtual functions are implemented by the peripheral
driver. </p>
<ul>
<li id="GUID-C5E97751-13E6-5439-AA62-2323D4DA7A37"><p> <xref href="GUID-A789E0D6-74B2-517D-B73A-F9B11794F175.dita#GUID-A789E0D6-74B2-517D-B73A-F9B11794F175/GUID-6A4484AA-B10E-54D8-B32B-05583EB66841">PowerDown()</xref>  </p> </li>
<li id="GUID-44F74198-A6DA-56FA-AE39-AADBC3DFB79F"><p> <xref href="GUID-A789E0D6-74B2-517D-B73A-F9B11794F175.dita#GUID-A789E0D6-74B2-517D-B73A-F9B11794F175/GUID-389D4920-2956-5CBE-979E-30C23A0C3E49">PowerUp()</xref>  </p> </li>
</ul>
<p>Notes: </p>
<ol id="GUID-C1640CE7-AF3E-5EF4-9D4C-B44F19B83AB3">
<li id="GUID-757692DC-EE42-577F-8D92-AC1C61A7C381"><p>Current consumption
monitoring does not have a full implementation in the power manager at present.
It is unclear whether this will be ever required. However, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref> does
provide two functions: <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-01C1C7F2-CC98-303F-B044-90C1B96304B6"><apiname>DPowerHandler::SetCurrentConsumption()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-96524179-926E-371A-9694-235C4D3B6163"><apiname>DPowerHandler::DeltaCurrentConsumption()</apiname></xref> that
a power handler can use to track the peripheral's power consumption. Note
that this is not based on actual measurements. </p> <p> <codeph>SetCurrentConsumption()</codeph> sets
a target current consumption, usually at driver creation time. </p> <p> <codeph>DeltaCurrentConsumption()</codeph> changes
this target current consumption value, specifying a positive or a negative
value as appropriate; this might be called in response to an operation that
is about to start. </p> <p>Although we have described the context in which
these functions would be used, we recommend that you do not use them. </p> </li>
<li id="GUID-54F4071B-E8E3-5EC3-A7F3-26F74451C707"><p>Fixed media drivers
do not have a power handler. This means there is currently no mechanism to
power down media drivers and the associated fixed media when the system transitions
to a low power state. </p> </li>
<li id="GUID-AF58E9DB-F1E9-5802-A9E8-8744CBA6C461"><p>The <codeph>__NEW_POWER_HANDLERS</codeph> macro
is used to maintain backwards compatibility with the power model used in previous
versions of Symbian OS. If this macro is <i>not</i> defined, it is possible
for power handlers to revert back to the behaviour they present in Kernel
Architecture 1 (EKA1). </p> <p>If implementing an old style power handler,
the following functions will have to have an implementation provided by the
peripheral driver: </p> <codeblock id="GUID-8D7F6D5A-01C7-5F7B-BE25-11D4D3110A26" xml:space="preserve">virtual TInt DoPowerUp()
virtual void DoPowerDown(TUint32 /* aPowerDownMask */)
virtual void DoEmergencyPowerDown()
          </codeblock> <p>If using at least an old style power handler the
power manager will not complete any powering down (transition to <i>Off</i> or <i>Standby</i>).
Thus it is recommended that they not be used. </p> </li>
</ol>
<section id="GUID-6A4484AA-B10E-54D8-B32B-05583EB66841"><title>DPowerHandler::PowerDown()</title> <codeblock id="GUID-61142DAF-895E-5432-B9DB-01CF88C24F26" xml:space="preserve">virtual void PowerDown(TPowerState) = 0;</codeblock> <p><b>When
is it called?</b> </p> <p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::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> during a transition to the <i>Standby</i> or the <i>Off</i> state.
The <xref href="GUID-87AB8B20-04EE-31D2-8F3D-EA904D05B8D0.dita"><apiname>TPowerState</apiname></xref> argument specifies which of the two power
states is the target. </p> <p><b>Implementation issues</b> </p> <ol id="GUID-60A913E7-16A2-5350-ACC0-448B980C045E">
<li id="GUID-98DC816F-B1DE-5524-BCD6-A1AA9DADC05F"><p>After receiving a request
to power down, as a result of a system transition to the <i>Standby</i> or <i>Off</i> states,
a peripheral driver should perform the necessary activity to power down the
peripheral and ancillary hardware, unless it is required for the detection
of wake-up events. This activity might include requesting the removal of the
power supply and any other power resources. </p> </li>
<li id="GUID-3EA32F60-D2B5-522D-901F-91B9D802B67F"><p>The power down operation
can be done in the same thread in which <codeph>PowerDown()</codeph> runs,
i.e. synchronously, or it can run in another thread, i.e. asynchronously.
You would probably implement power down in another thread if the operation
were potentially slow. Once the peripheral has powered down, it must inform
the power manager by calling <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-EBE8CFF8-50BD-3AC3-A4C8-47094DA5674D"><apiname>DPowerHandler::PowerDownDone()</apiname></xref>,
and this function can be called from the same thread in which <codeph>PowerDown()</codeph> runs,
or it can be called from another thread. Two points to note: </p> <ul>
<li id="GUID-E108AAD0-6E84-5BF5-91DA-0EBACD909DA5"><p> <codeph>PowerDownDone()</codeph> can
be called before or after <codeph>PowerDown()</codeph> returns </p> </li>
<li id="GUID-0341DC51-FAFA-5CA0-8F11-E1BD7765DCD5"><p> <codeph>PowerDownDone()</codeph> cannot
be called before <codeph>PowerDown()</codeph> has been entered. </p> </li>
</ul> </li>
<li id="GUID-0DF3E109-1EE8-5760-BE17-0998CF32EC97"><p> <codeph>PowerDown()</codeph> is
only called on a transition to the <i>Standby</i> or the <i>Off</i> state.
If the peripheral hardware is powered down when the peripheral driver is closed,
or when the hardware resources are relinquished by the driver, then this is
managed by the driver alone. </p> </li>
<li id="GUID-C3E38B61-7417-5C1A-AB24-355738BCD3EF"><p>There are synchronisation
issues related to calls to the <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref> functions. <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref> is called by the peripheral driver when the driver object is created. This
registers the power handler with the power manager so that so that the driver
can receive notification of power state transitions. Conversely, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref> is
called when the peripheral driver is in the process of being destroyed. This
de-registers the power handler so that the driver is no longer notified of
power state transitions. Calls to <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref>, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref> can run asynchronously in
relation to one another. For example, it is entirely possible that the kernel
may be asking the driver to power down while it is being created, or indeed
while it is being destroyed. </p> <p>To avoid deadlock, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref>, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>,
and 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> functions that call your <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref> and
your <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref> functions, all acquire a
lock, a <codeph>DMutex</codeph>. While the lock itself is internal to Symbian
OS, it does impose a requirement that: </p> <ul>
<li id="GUID-9C3D1630-F6BE-5B8F-8528-E6BF769BECAB"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref>  </p> </li>
<li id="GUID-104276CB-95F7-57BD-9988-BEEF1CE3255F"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>  </p> </li>
<li id="GUID-1B260C33-7697-5574-A623-15D9693DE21F"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref>  </p> </li>
<li id="GUID-0EBC4021-B090-5799-B0F6-3B2808FBBAB1"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref>  </p> </li>
</ul> <p>all run in the same thread. A common implementation of <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref>,
therefore, schedules a DFC to run on the same thread (a DFC queue) as the
one that calls <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>. </p> </li>
</ol> </section>
<section id="GUID-389D4920-2956-5CBE-979E-30C23A0C3E49"><title>DPowerHandler::PowerUp()</title> <codeblock id="GUID-F66A2F92-7C60-5D61-BEAD-392FA5F36830" xml:space="preserve">virtual void PowerUp() = 0;</codeblock> <p><b>When
is it called?</b> </p> <p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</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> during a transition from the <i>Standby</i> state back to the <i>Active</i> state.
It is up to the peripheral driver to decide whether or not to power up the
peripheral. </p> <p><b>Implementation issues</b> </p> <ol id="GUID-A0A555C9-516B-5408-AC8D-86F7F37501CA">
<li id="GUID-FF569561-DFB4-59F0-9665-34567D9E159A"><p>After receiving a notification
to power up, as a result of a system transition from the <i>Standby</i> to
the <i>Active</i> state, it is up to the peripheral driver to decide whether
or not to power up the peripheral and ancillary hardware. The decision usually
depends on whether or not the peripheral driver is currently in use. </p> </li>
<li id="GUID-C2317AFC-9615-56B3-83CC-B2A8F515FF01"><p>The power up operation
can be done in the same thread in which <codeph>PowerUp()</codeph> runs, i.e.
synchronously, or it can run in another thread, i.e. asynchronously. You would
probably implement power up in another thread if the operation were potentially
slow. Whether or not the peripheral driver intends to power up immediately,
it must acknowledge the power up request by calling <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-BF62042B-FB7B-3D5B-8379-490FBA284A7A"><apiname>DPowerHandler::PowerUpDone()</apiname></xref>,
and this function can be called from the same thread in which <codeph>PowerUp()</codeph> runs,
or it can be called from another thread. Two points to note: </p> <ul>
<li id="GUID-C8BA1C99-2731-56A0-96B1-99BF61DF7A46"><p> <codeph>PowerUpDone()</codeph> can
be called before or after <codeph>PowerUp()</codeph> returns </p> </li>
<li id="GUID-0CBF462D-12B9-5598-B968-00F69099E409"><p> <codeph>PowerUpDone()</codeph> cannot
be called before <codeph>PowerUp()</codeph> has been entered. </p> </li>
</ul> </li>
<li id="GUID-C64797E0-F77B-55D8-8BBC-C0335174B0DF"><p> <codeph>PowerUp()</codeph> is
only called on a transition to the <i>Active</i> state. If the peripheral
hardware is powered up when the peripheral driver is opened, or when the hardware
resources are first used by the driver, then this is managed by the driver
alone. </p> </li>
<li id="GUID-534A5CAA-4FF8-596A-AC79-DBFB31ACF1B9"><p>There are synchronisation
issues related to calls to the <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref> functions. <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref> is called by the peripheral driver when the driver object is created. This
registers the power handler with the power manager so that so that the driver
can receive notification of power state transitions. Conversely, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref> is
called when the peripheral driver is in the process of being destroyed. This
de-registers the power handler so that the driver is no longer notified of
power state transitions. Calls to <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref>, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref> can run asynchronoulsy in
relation to one another. For example, it is entirely possible that the kernel
may be asking the driver to power down while it is being created, or indeed
while it is being destroyed. </p> <p>To avoid deadlock, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref>, <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>,
and 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> functions that call your <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref> and
your <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref> functions, all acquire a
lock, a <codeph>DMutex</codeph>. While the lock itself is internal to Symbian
OS, it does impose a requirement that: </p> <ul>
<li id="GUID-6A297274-057E-5549-A2D6-6E4FE0D1FDD0"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref>  </p> </li>
<li id="GUID-8C902FBC-D818-5A56-ADBB-5B7E0C01C192"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>  </p> </li>
<li id="GUID-352D5DD5-FE31-5FF9-A988-E0E4D31BD687"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref>  </p> </li>
<li id="GUID-BB116FED-0F67-57B1-98DA-1F5A3BF2E61D"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref>  </p> </li>
</ul> <p>all run in the same thread. A common implementation of <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref>,
therefore, schedules a DFC to run on the same thread (a DFC queue) as the
one that calls <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-E8353DF6-B21B-383F-99AB-94B6B5139E47"><apiname>DPowerHandler::Add()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-FD0BA400-FDCD-3E8C-9130-992A95A3FF84"><apiname>DPowerHandler::Remove()</apiname></xref>. </p> </li>
</ol> </section>
</conbody></concept>