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<HTML
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><HEAD
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><TITLE
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>Changing Power Modes</TITLE
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><meta name="MSSmartTagsPreventParsing" content="TRUE">
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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"><LINK
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REL="HOME"
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TITLE="eCos Reference Manual"
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HREF="ecos-ref.html"><LINK
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REL="UP"
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TITLE="eCos Power Management Support"
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HREF="services-power.html"><LINK
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REL="PREVIOUS"
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TITLE="Power Management Information"
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HREF="power-info.html"><LINK
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REL="NEXT"
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TITLE="Support for Policy Modules"
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HREF="power-policy.html"></HEAD
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><BODY
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>eCos Reference Manual</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="power-info.html"
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ACCESSKEY="P"
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>Prev</A
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WIDTH="80%"
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="power-policy.html"
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ACCESSKEY="N"
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>Next</A
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="POWER-CHANGE">Changing Power Modes</H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN15752"
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></A
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><H2
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>Name</H2
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>Changing Power Modes -- reducing or increasing power consumption as needed</DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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><A
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NAME="AEN15755"><H2
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>Synopsis</H2
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><DIV
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CLASS="FUNCSYNOPSIS"
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><A
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NAME="AEN15756"><P
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></P
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><TABLE
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BORDER="5"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="FUNCSYNOPSISINFO"
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>#include <cyg/power/power.h></PRE
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></TD
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></TR
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></TABLE
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><P
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><CODE
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><CODE
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CLASS="FUNCDEF"
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> void power_set_mode
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</CODE
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>( PowerMode new_mode
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);</CODE
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></P
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><P
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><CODE
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><CODE
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CLASS="FUNCDEF"
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> void power_set_controller_mode
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</CODE
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>( PowerController* controller
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, PowerMode new_mode
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);</CODE
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></P
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><P
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><CODE
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><CODE
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CLASS="FUNCDEF"
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> void power_set_controller_mode_now
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</CODE
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>( PowerController* controller
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, PowerMode new_mode
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);</CODE
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></P
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><P
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></P
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></DIV
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="POWER-CHANGE-GLOBAL"
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></A
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><H2
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>Changing the Global Power Mode</H2
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><P
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>The primary functionality supported by the power management package is
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to change the system's global power mode. This is achieved by calling
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the function <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> with a single
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argument, which should be one of <TT
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CLASS="LITERAL"
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>PowerMode_Active</TT
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>,
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<TT
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CLASS="LITERAL"
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>PowerMode_Idle</TT
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>, <TT
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CLASS="LITERAL"
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>PowerMode_Sleep</TT
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>
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or <TT
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CLASS="LITERAL"
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>PowerMode_Off</TT
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>. Typically this function will only
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be invoked in certain scenarios:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>A typical system will contain a policy module which is primarily
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responsible for initiating power mode changes, and a thread inside the
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power management package. The policy module will call
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<TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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>, which has the effect of
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manipulating some internal state in the power management package and
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waking up its thread. When this thread gets scheduled to run (its
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priority is controlled by a configuration option), it will iterate
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over the power controllers and invoke each controller to change its
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power mode. There is support for a <A
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HREF="power-policy.html#POWER-POLICY-CALLBACK"
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>callback function</A
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>, and for
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<A
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HREF="power-attached.html"
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>detached</A
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> power controllers.</P
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></LI
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><LI
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><P
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>After a call to <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> but before the
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power management thread has had a chance to iterate over all the
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controllers, or even before the thread has been rescheduled at all,
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the policy module may decide that a different power mode would be more
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appropriate for the current situation and calls
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<TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> again. This has the effect of
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aborting the previous mode change, followed by the power management
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thread iterating over the power controllers again for the new mode.</P
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></LI
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><LI
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><P
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>If there is no single policy module responsible for power mode
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changes, any code can call <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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>. If
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there are multiple calls in quick succession, earlier calls will
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be aborted and the system should end up in the power mode
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corresponding to the last call</P
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></LI
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| 230 |
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><LI
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><P
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>As a special case, it is possible for a power controller to call
|
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<TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> when invoked by the power
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management thread. For example a power controller could decide that it
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is inappropriate for the system to go to sleep because the device it
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is associated with is still busy. The effect is as if the policy
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module had called <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> again before
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the mode change had completed.</P
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|
></LI
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| 246 |
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></OL
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><P
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>If the power management package has been configured not to use a
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separate thread then obviously the behaviour is somewhat different.
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The call to <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> will now iterate over
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the various power controllers immediately, rather than leaving this to
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a separate thread, and the whole mode change completes before
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<TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> returns. If some other thread or a
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DSR calls <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> concurrently the
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behaviour of the system is undefined. However, it is still legal for a
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power controller to call <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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>:
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effectively this is a recursive call; it is detected by the system,
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and internal state is updated; the recursive
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<TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> call now returns, and when the
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power controller returns back to the original
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<TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> call it detects what has happened,
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aborts the previous mode change, and starts a new mode change as
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requested by the controller.</P
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><P
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><TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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> is normally invoked from thread
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context. If a separate power management thread is used it can be
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invoked safely from DSR context. If the system is configured not to
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use such a thread, it may or may not be safe to invoke this function
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from DSR context: essentially the function just iterates through
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the various power controllers, and the documentation or source code of
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each controller present in the current system will have to be examined
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to determine whether or not this can happen safely in DSR context.
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<TT
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|
CLASS="FUNCTION"
|
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>power_set_mode</TT
|
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> should never be invoked from
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ISR context.</P
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| 299 |
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|
></DIV
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| 300 |
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><DIV
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| 301 |
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|
CLASS="REFSECT1"
|
| 302 |
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><A
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| 303 |
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NAME="POWER-CHANGE-CONTROLLER"
|
| 304 |
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></A
|
| 305 |
|
|
><H2
|
| 306 |
|
|
>Manipulating an Individual Power Controller</H2
|
| 307 |
|
|
><P
|
| 308 |
|
|
>In some cases it is desirable to set the power mode of an individual
|
| 309 |
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controller separately from the mode for the system as a whole. For
|
| 310 |
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example if a device is not currently being used then the associated
|
| 311 |
|
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power controller could be set to <TT
|
| 312 |
|
|
CLASS="LITERAL"
|
| 313 |
|
|
>PowerMode_Off</TT
|
| 314 |
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|
>,
|
| 315 |
|
|
even while the system as a whole is still active. This can be achieved
|
| 316 |
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|
by calling the function
|
| 317 |
|
|
<TT
|
| 318 |
|
|
CLASS="FUNCTION"
|
| 319 |
|
|
>power_set_controller_mode</TT
|
| 320 |
|
|
>. It takes two
|
| 321 |
|
|
arguments: the first identifies a particular controller; the second
|
| 322 |
|
|
specifies the desired new power mode for that controller. The function
|
| 323 |
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|
operates in much the same way as <TT
|
| 324 |
|
|
CLASS="FUNCTION"
|
| 325 |
|
|
>power_set_mode</TT
|
| 326 |
|
|
>,
|
| 327 |
|
|
for example if a separate power management thread is being used then
|
| 328 |
|
|
<TT
|
| 329 |
|
|
CLASS="FUNCTION"
|
| 330 |
|
|
>power_set_controller_mode</TT
|
| 331 |
|
|
> operates by
|
| 332 |
|
|
manipulating some internal state and waking up that thread. The
|
| 333 |
|
|
limitations are also much the same as for
|
| 334 |
|
|
<TT
|
| 335 |
|
|
CLASS="FUNCTION"
|
| 336 |
|
|
>power_set_mode</TT
|
| 337 |
|
|
>, so for example
|
| 338 |
|
|
<TT
|
| 339 |
|
|
CLASS="FUNCTION"
|
| 340 |
|
|
>power_set_controller_mode</TT
|
| 341 |
|
|
> should not be invoked
|
| 342 |
|
|
from inside ISRs.</P
|
| 343 |
|
|
><P
|
| 344 |
|
|
>Manipulating individual controllers is often used in conjunction with
|
| 345 |
|
|
the function <A
|
| 346 |
|
|
HREF="power-attached.html"
|
| 347 |
|
|
><TT
|
| 348 |
|
|
CLASS="FUNCTION"
|
| 349 |
|
|
>power_set_controller_attached</TT
|
| 350 |
|
|
></A
|
| 351 |
|
|
>,
|
| 352 |
|
|
allowing the policy module to specify which controllers are affected
|
| 353 |
|
|
by global mode changes.</P
|
| 354 |
|
|
></DIV
|
| 355 |
|
|
><DIV
|
| 356 |
|
|
CLASS="REFSECT1"
|
| 357 |
|
|
><A
|
| 358 |
|
|
NAME="POWER-CHANGE-CONTROLLER-NOW"
|
| 359 |
|
|
></A
|
| 360 |
|
|
><H2
|
| 361 |
|
|
>Direct Manipulation of a Power Controller</H2
|
| 362 |
|
|
><P
|
| 363 |
|
|
>In exceptional circumstances it may be necessary to invoke a power
|
| 364 |
|
|
controller directly, bypassing the power management thread and
|
| 365 |
|
|
higher-level functionality such as <A
|
| 366 |
|
|
HREF="power-policy.html#POWER-POLICY-CALLBACK"
|
| 367 |
|
|
>callback functions</A
|
| 368 |
|
|
>. The
|
| 369 |
|
|
function <TT
|
| 370 |
|
|
CLASS="FUNCTION"
|
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>power_set_controller_mode_now</TT
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> allows
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this. It takes two arguments, a controller and a mode, just like
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<TT
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>power_set_controller_mode</TT
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>.</P
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><P
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>Use of <TT
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CLASS="FUNCTION"
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>power_set_controller_mode_now</TT
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> is
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dangerous. For example no attempt is made to synchronise with any
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other power mode changes that might be happening concurrently. A
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possible use is when the system gets woken up out of
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<SPAN
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CLASS="TYPE"
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>sleep</SPAN
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> mode: depending on the hardware, on which power
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controllers are present, and on the application code it may be
|
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necessary to wake up some power controllers immediately before the
|
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system as a whole is ready to run again.</P
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="power-info.html"
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>Prev</A
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VALIGN="top"
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><A
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HREF="ecos-ref.html"
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>Home</A
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>Power Management Information</TD
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