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><H1
><A
NAME="POWER-INFO">Power Management Information</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN15678"
></A
><H2
>Name</H2
>Obtaining Power Management Information -- finding out about the various power controllers in the system</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN15681"><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN15682"><P
></P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include <cyg/power/power.h>
extern PowerController __POWER__[], __POWER_END__;
extern PowerController power_controller_cpu;
extern cyg_handle_t power_thread_handle;</PRE
></TD
></TR
></TABLE
><P
><CODE
><CODE
CLASS="FUNCDEF"
> PowerMode power_get_mode
</CODE
>(void);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
> PowerMode power_get_desired_mode
</CODE
>(void);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
> PowerMode power_get_controller_mode
</CODE
>( PowerController* controller
);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
> PowerMode power_get_controller_desired_mode
</CODE
>( PowerController* controller
);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
> const char* power_get_controller_id
</CODE
>( PowerController* controller
);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="POWER-INFO-ACCESS"
></A
><H2
>Accessing Power Controllers</H2
><P
>All the power controllers in a system are held in a table, filled in
at link-time. The symbols <TT
CLASS="VARNAME"
>__POWER__</TT
> and
<TT
CLASS="VARNAME"
>__POWER_END</TT
> can be used to iterate through this
table, for example:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>PowerController* controller;
for (controller = &(__POWER__[0]);
controller != &(__POWER_END__);
controller++) {
…
}</PRE
></TD
></TR
></TABLE
><P
>Each controller has an associated priority, controlling the order in
which they appear in the table. Typically a software-only component
such as a TCP/IP stack would use a small number for the priority, so
that it appears near the start of the table, whereas a device driver
would be nearer the back of the table. When switching to a
lower-powered mode the power management package will iterate through
this table from front to back, thus ensuring that for example the
TCP/IP stack gets a chance to shut down before the underlying ethernet
or other hardware that the stack depends on. Similarly when switching
to a higher-powered mode the power management package will iterate
through this table from back to front.</P
><P
>In most systems there will be one special controller,
<TT
CLASS="VARNAME"
>power_controller_cpu</TT
>, which should be provided by
one of the architectural, variant or platform HAL packages. This
controller will always be the last entry in the table. It is
responsible for the final power down operation when switching to
<SPAN
CLASS="TYPE"
>off</SPAN
> mode. Other packages such as device drivers may or
may not declare variable identifiers for their power controllers,
allowing those controllers to be accessed by name as well as by their
entries in the global table.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="POWER-INFO-GLOBAL"
></A
><H2
>Global Power Modes</H2
><P
>The function <TT
CLASS="FUNCTION"
>power_get_mode</TT
> can be called at any
time to determine the current power mode for the system as a whole.
The return value will be one of <TT
CLASS="LITERAL"
>PowerMode_Active</TT
>,
<TT
CLASS="LITERAL"
>PowerMode_Idle</TT
>, <TT
CLASS="LITERAL"
>PowerMode_Sleep</TT
>
or <TT
CLASS="LITERAL"
>PowerMode_Off</TT
>. In normal circumstances it is
unlikely that <TT
CLASS="LITERAL"
>PowerMode_Off</TT
> would be returned since
that mode generally means that the cpu is no longer running.</P
><P
>The function <TT
CLASS="FUNCTION"
>power_get_desired_mode</TT
> returns the
power mode that the system should be running at. Most of the time this
will be the same value as returned by
<TT
CLASS="FUNCTION"
>power_get_mode</TT
>. However a different value may be
returned when in the middle of changing power modes. For example, if
the current thread runs at a higher priority than the power management
thread then the latter may have been pre-empted in the middle of a
mode change: <TT
CLASS="FUNCTION"
>power_get_mode</TT
> will return the mode
the system was running at before the mode change started, and
<TT
CLASS="FUNCTION"
>power_get_desired_mode</TT
> will return the mode the
system should end up in when the mode change completes, barring
further calls to <TT
CLASS="FUNCTION"
>power_set_mode</TT
>.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="POWER-INFO-INDIVIDUAL"
></A
><H2
>Individual Controller Power Modes</H2
><P
>The power management package keeps track of the current and desired
modes for each power controller, as well as the modes for the system as
a whole. The function <TT
CLASS="FUNCTION"
>power_get_controller_mode</TT
>
takes a single argument, a pointer to a power controller, and returns
the power mode that controller is currently running at. Similarly
<TT
CLASS="FUNCTION"
>power_get_controller_desired_mode</TT
> returns the
power mode that controller should be running at. Most of the time the
current and desired modes for a given controller will be the same, and
will also be the same as the global power mode. However if the power
management thread is preeempted in the middle of a mode change then
some of the controllers will have been updated to the desired global
mode, whereas others will still be at the old mode. The power
management package also provides functionality for manipulating
<A
HREF="power-change.html#POWER-CHANGE-CONTROLLER"
>individual controllers</A
>, and for <A
HREF="power-attached.html"
>detaching</A
> controllers from
global mode changes.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="POWER-INFO-IDS"
></A
><H2
>Power Controller Identification</H2
><P
>In some scenarios the power management package will run completely
automated, and there is no need to identify individual power
controllers. Any form of identification such as a string
description would serve no purpose, but would still consume memory in
the final system. In other scenarios it may be very desirable to
provide some means of identification. For example, while still
debugging it may be useful to see a simple string when printing the
contents of a power controller structure. Alternatively, if the
application is expected to provide some sort of user interface that
gives control over which parts of the system are enabled or disabled,
a string identifier for each controller would be useful. To cope with
these scenarios the power management package provides a configuration
option <TT
CLASS="VARNAME"
>CYGIMP_POWER_PROVIDE_STRINGS</TT
>. When enabled,
each power controller will contain a pointer to a constant string
which can be accessed via a function
<TT
CLASS="FUNCTION"
>power_get_controller_id</TT
>. When disabled the system
will not contain these strings, and the function will not be provided.
The following code illustrates how to use this function.</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#include <stdio.h>
#include <pkgconf/system.h>
#ifndef CYGPKG_POWER
# error The power management package is not present.
#endif
#include <pkgconf/power.h>
#ifndef CYGIMP_POWER_PROVIDE_STRINGS
# error Power controller identifiers are not available.
#endif
#include <cyg/power/power.h>
static const char*
mode_to_string(PowerMode mode)
{
const char* result;
switch(mode) {
case PowerMode_Active : result = "active"; break;
case PowerMode_Idle : result = "idle"; break;
case PowerMode_Sleep : result = "sleep"; break;
case PowerMode_Off : result = "off"; break;
default : result = "<unknown>"; break;
}
return result;
}
int
main(int argc, char** argv)
{
PowerController* controller;
for (controller = &(__POWER__[0]);
controller != &(__POWER_END__);
controller++) {
printf("Controller @ %p: %s, %s\n", controller,
power_get_controller_id(controller),
mode_to_string(power_get_controller_mode(controller)));
}
return 0;
}</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="POWER-INFO-THREAD"
></A
><H2
>The Power Management Thread</H2
><P
>If the power management package is configured to use a separate thread
then a handle for that thread is made available to higher-level code
via the variable <TT
CLASS="VARNAME"
>power_thread_handle</TT
>. This handle
can be used for a variety of purposes, including manipulating that
thread's priority.</P
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