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>Power Management Information</TITLE
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TITLE="eCos Power Management Support"
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TITLE="Introduction"
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TITLE="Changing Power Modes"
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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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><A
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HREF="power-intro.html"
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><HR
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="POWER-INFO">Power Management Information</H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN15678"
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></A
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><H2
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>Name</H2
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>Obtaining Power Management Information&nbsp;--&nbsp;finding out about the various power controllers in the system</DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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><A
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NAME="AEN15681"><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="AEN15682"><P
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></P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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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 &lt;cyg/power/power.h&gt;
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extern PowerController __POWER__[], __POWER_END__;
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extern PowerController power_controller_cpu;
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extern cyg_handle_t    power_thread_handle;</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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>    PowerMode power_get_mode
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  </CODE
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>(void);</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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>    PowerMode power_get_desired_mode
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  </CODE
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>(void);</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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>    PowerMode power_get_controller_mode
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  </CODE
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>(    PowerController* controller
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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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>    PowerMode power_get_controller_desired_mode
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  </CODE
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>(    PowerController* controller
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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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>    const char* power_get_controller_id
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  </CODE
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>(    PowerController* controller
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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-INFO-ACCESS"
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></A
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><H2
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>Accessing Power Controllers</H2
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><P
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>All the power controllers in a system are held in a table, filled in
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at link-time. The symbols <TT
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CLASS="VARNAME"
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>__POWER__</TT
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> and
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<TT
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CLASS="VARNAME"
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>__POWER_END</TT
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> can be used to iterate through this
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table, for example:</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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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="PROGRAMLISTING"
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>PowerController* controller;
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for (controller  = &amp;(__POWER__[0]);
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     controller != &amp;(__POWER_END__);
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     controller++) {
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     &#8230;
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}</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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>Each controller has an associated priority, controlling the order in
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which they appear in the table. Typically a software-only component
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such as a TCP/IP stack would use a small number for the priority, so
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that it appears near the start of the table, whereas a device driver
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would be nearer the back of the table. When switching to a
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lower-powered mode the power management package will iterate through
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this table from front to back, thus ensuring that for example the
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TCP/IP stack gets a chance to shut down before the underlying ethernet
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or other hardware that the stack depends on. Similarly when switching
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to a higher-powered mode the power management package will iterate
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through this table from back to front.</P
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><P
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>In most systems there will be one special controller,
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<TT
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CLASS="VARNAME"
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>power_controller_cpu</TT
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>, which should be provided by
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one of the architectural, variant or platform HAL packages. This
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controller will always be the last entry in the table. It is
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responsible for the final power down operation when switching to
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<SPAN
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CLASS="TYPE"
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>off</SPAN
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> mode. Other packages such as device drivers may or
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may not declare variable identifiers for their power controllers,
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allowing those controllers to be accessed by name as well as by their
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entries in the global table.</P
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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-INFO-GLOBAL"
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></A
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><H2
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>Global Power Modes</H2
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><P
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>The function <TT
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CLASS="FUNCTION"
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>power_get_mode</TT
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> can be called at any
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time to determine the current power mode for the system as a whole.
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The return value will 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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>. In normal circumstances it is
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unlikely that <TT
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CLASS="LITERAL"
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>PowerMode_Off</TT
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> would be returned since
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that mode generally means that the cpu is no longer running.</P
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><P
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>The function <TT
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CLASS="FUNCTION"
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>power_get_desired_mode</TT
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> returns the
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power mode that the system should be running at. Most of the time this
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will be the same value as returned by
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<TT
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CLASS="FUNCTION"
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>power_get_mode</TT
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>. However a different value may be
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returned when in the middle of changing power modes. For example, if
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the current thread runs at a higher priority than the power management
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thread then the latter may have been pre-empted in the middle of a
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mode change: <TT
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CLASS="FUNCTION"
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>power_get_mode</TT
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> will return the mode
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the system was running at before the mode change started, and
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<TT
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CLASS="FUNCTION"
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>power_get_desired_mode</TT
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> will return the mode the
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system should end up in when the mode change completes, barring
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further calls to <TT
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CLASS="FUNCTION"
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>power_set_mode</TT
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>.</P
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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-INFO-INDIVIDUAL"
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></A
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><H2
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>Individual Controller Power Modes</H2
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><P
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>The power management package keeps track of the current and desired
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modes for each power controller, as well as the modes for the system as
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a whole. The function <TT
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CLASS="FUNCTION"
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>power_get_controller_mode</TT
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>
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takes a single argument, a pointer to a power controller, and returns
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the power mode that controller is currently running at. Similarly
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<TT
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CLASS="FUNCTION"
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>power_get_controller_desired_mode</TT
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> returns the
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power mode that controller should be running at. Most of the time the
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current and desired modes for a given controller will be the same, and
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will also be the same as the global power mode. However if the power
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management thread is preeempted in the middle of a mode change then
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some of the controllers will have been updated to the desired global
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mode, whereas others will still be at the old mode. The power
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management package also provides functionality for manipulating
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<A
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HREF="power-change.html#POWER-CHANGE-CONTROLLER"
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>individual controllers</A
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>, and for <A
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HREF="power-attached.html"
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>detaching</A
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> controllers from
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global mode changes.</P
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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-INFO-IDS"
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></A
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><H2
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>Power Controller Identification</H2
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><P
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>In some scenarios the power management package will run completely
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automated, and there is no need to identify individual power
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controllers. Any form of identification such as a string
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description would serve no purpose, but would still consume memory in
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the final system. In other scenarios it may be very desirable to
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provide some means of identification. For example, while still
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debugging it may be useful to see a simple string when printing the
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contents of a power controller structure. Alternatively, if the
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application is expected to provide some sort of user interface that
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gives control over which parts of the system are enabled or disabled,
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a string identifier for each controller would be useful. To cope with
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these scenarios the power management package provides a configuration
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option <TT
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CLASS="VARNAME"
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>CYGIMP_POWER_PROVIDE_STRINGS</TT
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>. When enabled,
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each power controller will contain a pointer to a constant string
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which can be accessed via a function
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<TT
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CLASS="FUNCTION"
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>power_get_controller_id</TT
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>. When disabled the system
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will not contain these strings, and the function will not be provided.
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The following code illustrates how to use this function.</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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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="PROGRAMLISTING"
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>#include &lt;stdio.h&gt;
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#include &lt;pkgconf/system.h&gt;
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#ifndef CYGPKG_POWER
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# error The power management package is not present.
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#endif
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#include &lt;pkgconf/power.h&gt;
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#ifndef CYGIMP_POWER_PROVIDE_STRINGS
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# error Power controller identifiers are not available.
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#endif
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#include &lt;cyg/power/power.h&gt;
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static const char*
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mode_to_string(PowerMode mode)
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{
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    const char* result;
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    switch(mode) {
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      case PowerMode_Active : result = "active"; break;
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      case PowerMode_Idle   : result = "idle"; break;
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      case PowerMode_Sleep  : result = "sleep"; break;
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      case PowerMode_Off    : result = "off"; break;
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      default               : result = "&lt;unknown&gt;"; break;
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    }
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    return result;
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}
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int
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main(int argc, char** argv)
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{
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    PowerController* controller;
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397 
    for (controller = &amp;(__POWER__[0]);
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         controller != &amp;(__POWER_END__);
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         controller++) {
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        printf("Controller @ %p: %s, %s\n", controller,
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               power_get_controller_id(controller),
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               mode_to_string(power_get_controller_mode(controller)));
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    }
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    return 0;
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}</PRE
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></TD
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></TR
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></TABLE
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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-INFO-THREAD"
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></A
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><H2
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>The Power Management Thread</H2
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><P
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>If the power management package is configured to use a separate thread
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then a handle for that thread is made available to higher-level code
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via the variable <TT
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CLASS="VARNAME"
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>power_thread_handle</TT
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>. This handle
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can be used for a variety of purposes, including manipulating that
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thread's priority.</P
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>Introduction</TD
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>Up</A
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>Changing Power Modes</TD
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