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<title>Power Management of Non-Virtualised Devices</title>
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<body>
-<div class="document" id="power-management-of-non-virtualised-devices">
<h1 class="title">Power Management of Non-Virtualised Devices</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<td>Kevin Klues, Vlado Handziski, Jan-Hinrich Hauer, Phil Levis</td></tr>
<tr class="field"><th class="docinfo-name">Draft-Created:</th><td class="field-body">11-Jan-2006</td>
</tr>
-<tr class="field"><th class="docinfo-name">Draft-Version:</th><td class="field-body">1.5</td>
+<tr class="field"><th class="docinfo-name">Draft-Version:</th><td class="field-body">1.7</td>
</tr>
-<tr class="field"><th class="docinfo-name">Draft-Modified:</th><td class="field-body">2006-12-12</td>
+<tr class="field"><th class="docinfo-name">Draft-Modified:</th><td class="field-body">2007-02-21</td>
</tr>
-<tr class="field"><th class="docinfo-name">Draft-Discuss:</th><td class="field-body">TinyOS Developer List
+<tr class="field"><th class="docinfo-name">Draft-Discuss:</th><td class="field-body">TinyOS Developer List
<tinyos-devel at mail.millennium.berkeley.edu></td>
</tr>
</tbody>
</table>
+<div class="document" id="power-management-of-non-virtualised-devices">
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">This memo documents a part of TinyOS for the TinyOS Community, and
of this memo is unlimited. This memo is in full compliance with TEP
1.</p>
</div>
-<div class="section">
-<h1><a id="abstract" name="abstract">Abstract</a></h1>
+<div class="section" id="abstract">
+<h1><a name="abstract">Abstract</a></h1>
<p>This memo documents how TinyOS 2.x manages the power state of physical
(not virtualised) abstractions.</p>
</div>
-<div class="section">
-<h1><a id="introduction" name="introduction">1. Introduction</a></h1>
-<p>The energy resources on a typical TinyOS platform are limited, so
-every effort should be made to put all devices on a given platform
-into their lowest possible power state as often as
-possible. Depending on the device type, selecting the correct
-power state could be as simple as switching between on and
-off states, or involve selecting the optimum state from among
-several. Choosing the best possible power state requires making
-tradeoffs between various factors such as power consumption, fidelity,
-performance, and wake-up latency.</p>
-<p>Unfortunately, it is not feasible do design a unified one size-fits-all power
-management strategy for use by all types of devices. Some devices
-(particularly microcontollers) have direct access to internal registers that
-allow them to efficiently calculate their lowest possible power state
-very quickly. Other devices do not have this information readily available and
-would have to calculate it on the fly if other mechanisms were not in place to
-prevent this. Designing a general system wide power control algorithm to handle
-all such devices would most likely be overly complex and in some cases even
-suboptimal. TinyOS 2.x, therefore, takes the approach of defining two different
-classes of devices for which different power-management strategies have been
-optimized: microcontrollers and peripheral devices. As opposed to microcontrollers,
-which normally contain a number of different valid power states, peripheral devices
-tend to have only two distinct states they can be switched to (<em>on</em> and <em>off</em>). Even
-in the rare case where a device of this type happens to contain multiple power
-states, TinyOS has traditionally used just the two most useful power states and
-designated them to mean either <em>on</em> or <em>off</em>. This TEP is dedicated to
-describing power management for peripheral devices of this type. Details on the
-mechanisms used to perform microcontroller power management can be found in <a class="citation-reference" href="#tep112" id="id1" name="id1">[TEP112]</a>.</p>
-<p>The term "peripheral device" specifically refers to any hardware device for which
-the mechanisms described in <a class="citation-reference" href="#tep108" id="id2" name="id2">[TEP108]</a> can be used to provide resource arbitration
-for them. These devices are considered <em>non-virtualised</em> in the sense that
-access to them must be explicitly requested and released by higher level
-components wishing to use them. Various policies can be implemented on top of
-this class of devices to decide exactly when they should be powered on or off.
-The simplest policy involves leaving it up to the programmer
-to ensure that a device is switched on or off whenever it should be.
-Other policies involve automatically powering a device up or down
-by monitoring whether any clients are currently connected to it
-or not. Depending on the type of power management policy desired,
-different models should be followed when designing drivers for devices
-of this class.</p>
+<div class="section" id="introduction">
+<h1><a name="introduction">1. Introduction</a></h1>
+<p>TinyOS platforms have limited energy. A unified power management
+strategy for all devices and peripherpals is not feasible, as
+they vary significantly in warm-up times, power profiles, and
+operation latencies. While some devices, such as
+microcontrollers, can efficiently calculate their lowest possible
+power state very quickly, others, such as sensors with warm-up
+times, require external knowledge to do so.</p>
+<p>In TinyOS 1.x, an application is responsible for all power management.
+Low-level subsystems, such as an SPI bus, are explicitly powered on
+and off by higher level abstractions. This approach of deep calls
+to StdControl.start and StdControl.stop introduces strange behaviors
+and can get in the way of power conservation. Turning off the radio
+on the Telos platform, for example, turns off the SPI bus and therefore
+prevents the flash driver from working. Additionally, the microcontroller
+stays in a higher power state for the SPI bus even when it is
+inactive.</p>
+<p>TinyOS 2.x defines two classes of devices for power-management:
+microcontrollers and peripherals. TEP 112 documents how TinyOS 2.x
+manages the power state of a microcontroller <a class="citation-reference" href="#tep112" id="id1" name="id1">[TEP112]</a>.
+Unlike microcontrollers, which typically have several power states,
+peripheral devices typically have two distinct states, <em>on</em> and <em>off</em>.
+This TEP is dedicated to documenting how TinyOS 2.x controls the power
+state of peripheral devices.</p>
+<p>The term "peripheral device" refers to any hardware device which
+arbitrates access with the mechanisms described in <a class="citation-reference" href="#tep108" id="id2" name="id2">[TEP108]</a> . These
+devices are not virtualised in the sense that access to
+them must be explicitly requested and released by their users.</p>
</div>
-<div class="section">
-<h1><a id="power-management-models" name="power-management-models">2. Power Management Models</a></h1>
-<p>In order to support both manual and automatic power management of
-non-virtualised devices in TinyOS, two different power management models have
-been defined: <em>explicit power management</em> and <em>implicit power management</em>.</p>
-<p>The <em>explicit power management</em> model provides a means for a single
-client to manually control the power state of a dedicated physical device
-(as defined by <a class="citation-reference" href="#tep108" id="id3" name="id3">[TEP108]</a>). Whenever this client tells the device to
-power up or down it does so without delay. This model can be
-particularly useful when the control information driving the selection
-of the proper power state of a device relies on external logic contained in
-higher level components. The following section discusses the <tt class="docutils literal"><span class="pre">StdControl</span></tt>,
-<tt class="docutils literal"><span class="pre">SplitControl</span></tt>, and <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt> interfaces used to perform power
-management of this type.</p>
-<p>The <em>implicit power management</em> model, on the other hand, provides a
-means for allowing the power state of a device to be controlled from
-within the driver for that device itself. Device drivers following
-this model are never explicitly powered up or down by some external
-client, but rather <em>require</em> some internal policy to be defined that
-decides exactly when their power states should be changed. This policy
-could exist natively on the hardware of the physical device itself, or
-be implemented on top of some lower level abstraction of a physical
+<div class="section" id="power-management-models">
+<h1><a name="power-management-models">2. Power Management Models</a></h1>
+<p>There are two different models to managing the power state of a
+peripheral in TinyOS: <em>explicit power management</em> and <em>implicit
+power management</em>.</p>
+<p>The explicit model provides a means for a single client to manually
+control the power state of a dedicated physical device (as defined by
+<a class="citation-reference" href="#tep108" id="id3" name="id3">[TEP108]</a>). Whenever this client tells the device to power up or down
+it does so without delay (albeit that caused by hardware). This model
+can be particularly useful when the control information driving the
+selection of the proper power state of a device relies on external
+logic contained in higher level components. The following section
+discusses the <tt class="docutils literal"><span class="pre">StdControl</span></tt>, <tt class="docutils literal"><span class="pre">SplitControl</span></tt>, and
+<tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt> interfaces used to perform power management of
+this type.</p>
+<p>The implicit model, on the other hand, provides a means for allowing
+the power state of a device to be controlled from within the driver
+for that device itself. Device drivers following this model are never
+explicitly powered up or down by some external client, but rather
+<em>require</em> some internal policy to be defined that decides exactly when
+their power states should be changed. This policy could exist
+natively on the hardware of the physical device itself, or be
+implemented on top of some lower level abstraction of a physical
device adhering to the <em>explicit power management</em> model.</p>
-<p>For shared devices (as defined by <a class="citation-reference" href="#tep108" id="id4" name="id4">[TEP108]</a>), the information required to
-determine if a device's clients require it to be powered on or not can
-be inferred through the set of interfaces they provide.
-Because of this fact, no StdControl-like interface needs to be provided
-to any higher level components, and the <em>implicit power management</em> policy
-in use can act accordingly whenever clients request or release the device.
+<p>Shared devices (as defined by <a class="citation-reference" href="#tep108" id="id4" name="id4">[TEP108]</a>) can infer whether they
+should be on or off based on the interfaces they provide to their
+clients. For example, when a client requests the ADC, this implies
+the ADC should be on; if there are no requests of the ADC, this implies
+it should be off. Therefore shared devices do not need to provide a
+power control interface. They can use an implicit power management policy.
Section 4.2 discusses this in more detail.:</p>
<pre class="literal-block">
/|\ /|\
| |
Data Interface Resource
- | |
+ | |
-----------------------------------------------------------------------
| Shared Device (implicitly power managed) |
-----------------------------------------------------------------------
--------------------------------- --------------------------------
</pre>
</div>
-<div class="section">
-<h1><a id="explicit-power-management" name="explicit-power-management">3. Explicit Power Management</a></h1>
-<p>Just as in TinyOS 1.x, <tt class="docutils literal"><span class="pre">StdControl</span></tt> and <tt class="docutils literal"><span class="pre">SplitControl</span></tt> interfaces have
-been defined for TinyOS 2.x in order to control the on and off power
-states of devices adhering to the <em>explicit power management</em> model.
-A third interface called <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt> has also been introduced
-for components in which it is critical to have the ability to power
-them on or off while running in asynchronous context. One of these
-three interfaces MUST be provided by components wrapping a hardware
-device that supports switching between the devices on and off power
-states. The selection of the right interface depends on the latencies
-involved in changing between these two states as well as the nature of
-the code (sync or async) executing any of the interfaces commands.</p>
-<div class="section">
-<h2><a id="power-management-with-stdcontrol" name="power-management-with-stdcontrol">3.1 Power Management with <tt class="docutils literal"><span class="pre">StdControl</span></tt></a></h2>
+<div class="section" id="explicit-power-management">
+<h1><a name="explicit-power-management">3. Explicit Power Management</a></h1>
+<p>Just as in TinyOS 1.x, TinyOS 2.x has <tt class="docutils literal"><span class="pre">StdControl</span></tt> and <tt class="docutils literal"><span class="pre">SplitControl</span></tt>
+interfaces in order to control the on and off
+power states of explicitly managed peripherals. TinyOS 2.x also
+introduces a third interface, <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt>. A component
+representing a hardware device that can be powered on and off MUST
+provide one of these three interfaces.
+The selection of the right interface depends on the
+latencies involved in changing between these two states as well as the
+nature of the code (sync or async) executing any of the interfaces
+commands.</p>
+<div class="section" id="power-management-with-stdcontrol">
+<h2><a name="power-management-with-stdcontrol">3.1 Power Management with <tt class="docutils literal"><span class="pre">StdControl</span></tt></a></h2>
<p>Whenever the powerup and powerdown times of a non-virtualised device
-are negligible, they SHOULD provide the <tt class="docutils literal"><span class="pre">StdControl</span></tt> interface as
+are negligible, they SHOULD provide the <tt class="docutils literal"><span class="pre">StdControl</span></tt> interface as
defined below:</p>
<pre class="literal-block">
interface StdControl {
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">Powerup and powerdown times on the order of a few microseconds have
-traditionally been considered negligible, and can be waited on using one of the
-<em>BusyWait</em> interfaces described in <a class="citation-reference" href="#tep102" id="id5" name="id5">[TEP102]</a>. Powerup and powerdown
-times on the order of a few milliseconds, however, should not be
-ignored, and MUST be hidden behind the use of the <tt class="docutils literal"><span class="pre">SplitControl</span></tt> interface
-described later on in this section.</p>
+traditionally been considered negligible, and can be waited on using
+one of the <em>BusyWait</em> interfaces described in <a class="citation-reference" href="#tep102" id="id5" name="id5">[TEP102]</a>. Powerup
+and powerdown times on the order of a few milliseconds, however,
+should not be ignored, and MUST be hidden behind the use of the
+<tt class="docutils literal"><span class="pre">SplitControl</span></tt> interface described later on in this section.
+A general rule of thumb is that if waiting for powerup takes
+more than one hundred microseconds, SplitControl is probably more
+suitable.</p>
</div>
<p>An external component MUST call <tt class="docutils literal"><span class="pre">StdControl.start()</span></tt> to power a
device on and <tt class="docutils literal"><span class="pre">StdControl.stop()</span></tt> to power a device off. Calls to
device MUST be completely powered on, allowing calls to commands of other
interfaces implemented by the device to succeed.</p>
<p>Upon the successful return of a call to <tt class="docutils literal"><span class="pre">StdControl.stop()</span></tt>, a
-device MUST be completely powered down, and any calls to commands
+device MUST be completely powered down, and any calls to commands
of other interfaces implemented by that device MUST return FAIL or EOFF.</p>
<p>If a device is not able to complete the <tt class="docutils literal"><span class="pre">StdControl.start()</span></tt> or
<tt class="docutils literal"><span class="pre">StdControl.stop()</span></tt> request for any reason, it MUST return FAIL.</p>
<col width="31%" />
</colgroup>
<thead valign="bottom">
-<tr><th class="head">Call</th>
-<th class="head">Device On</th>
-<th class="head">Device Off</th>
+<tr><th>Call</th>
+<th>Device On</th>
+<th>Device Off</th>
</tr>
</thead>
<tbody valign="top">
}
</pre>
</div>
-<div class="section">
-<h2><a id="power-management-with-splitcontrol" name="power-management-with-splitcontrol">3.2 Power Management with <tt class="docutils literal"><span class="pre">SplitControl</span></tt></a></h2>
+<div class="section" id="power-management-with-splitcontrol">
+<h2><a name="power-management-with-splitcontrol">3.2 Power Management with <tt class="docutils literal"><span class="pre">SplitControl</span></tt></a></h2>
<p>When a device's powerup and powerdown times are non-negligible, the
<em>``SplitControl``</em> interface MUST be used in place of the <em>``StdControl``</em>
interface. The definition of this interface can be seen below:</p>
</pre>
<p>An external component MUST call <tt class="docutils literal"><span class="pre">SplitControl.start()</span></tt> to power a
device on and <tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> to power a device off. Calls to
-either command return one of SUCCESS or FAIL.</p>
+either command return one of SUCCESS, FAIL, EBUSY, or
+EALREADY. SUCCESS indicates that the device has now started chaning
+its power mode and it will signal a corresponding completion event in
+the future. EBUSY indicates that the device is in the midst of the
+other operation (e.g., it is starting when stop is called or stopping
+when start is called) and will not issue an event. EALREADY indicates
+that the device is already in that state; the call is erroneus and a
+completion event will not be signaled. FAIL indicates that the
+device's power state could not be changed. More explicitly:</p>
<p>Successful calls to <tt class="docutils literal"><span class="pre">SplitControl.start()</span></tt> MUST signal one of
<tt class="docutils literal"><span class="pre">SplitControl.startDone(SUCCESS)</span></tt> or <tt class="docutils literal"><span class="pre">SplitControl.startDone(FAIL)</span></tt>.</p>
<p>Successful calls to <tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> MUST signal one of
<tt class="docutils literal"><span class="pre">SplitControl.stopDone(SUCCESS)</span></tt> or <tt class="docutils literal"><span class="pre">SplitControl.stopDone(FAIL)</span></tt>.</p>
<p>Upon signaling a <tt class="docutils literal"><span class="pre">SplitControl.startDone(SUCCESS)</span></tt>, a device MUST
-be completely powered on, and operation requests through calls to commands
+be completely powered on, and operation requests through calls to commands
of other interfaces implemented by the device MAY succeed.</p>
-<p>Upon signalling a <tt class="docutils literal"><span class="pre">SplitControl.stopDone(SUCCESS)</span></tt>, a device MUST be
-completely powered down, and any subsequent calls to commands of other
+<p>Upon signalling a <tt class="docutils literal"><span class="pre">SplitControl.stopDone(SUCCESS)</span></tt>, a device MUST be
+completely powered down, and any subsequent calls to commands of other
interfaces implemented by the device MUST return EOFF or FAIL.</p>
<p>If a device is powered on and a successful call to <tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt>
-signals a <tt class="docutils literal"><span class="pre">SplitControl.stopDone(FAIL)</span></tt>, the device MUST still be fully
-powered on, and operation requests through calls to commands of other
+signals a <tt class="docutils literal"><span class="pre">SplitControl.stopDone(FAIL)</span></tt>, the device MUST still be fully
+powered on, and operation requests through calls to commands of other
interfaces implemented by the device MAY succeed.</p>
-<p>If a device is powered down and a successful call to <tt class="docutils literal"><span class="pre">SplitControl.start()</span></tt>
-signals a <tt class="docutils literal"><span class="pre">SplitControl.startDone(FAIL)</span></tt>, the device MUST still be fully
-powered down, and operation requests through calls to commands of other
+<p>If a device is powered down and a successful call to <tt class="docutils literal"><span class="pre">SplitControl.start()</span></tt>
+signals a <tt class="docutils literal"><span class="pre">SplitControl.startDone(FAIL)</span></tt>, the device MUST still be fully
+powered down, and operation requests through calls to commands of other
interfaces implemented by the device MUST return EOFF or FAIL.</p>
<p>If a device is not able to complete the <tt class="docutils literal"><span class="pre">SplitControl.start()</span></tt> or
-<tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> requests for any reason, they MUST return
-FAIL.</p>
-<p>Calls to either <tt class="docutils literal"><span class="pre">StdControl.start()</span></tt> or <tt class="docutils literal"><span class="pre">StdControl.stop()</span></tt> while
-a start or stop operation is pending MUST return SUCCESS, with the
-anticipation that a corresponding <tt class="docutils literal"><span class="pre">StdControl.startDone()</span></tt> or
-<tt class="docutils literal"><span class="pre">StdControl.stopDone()</span></tt> will be signaled in the future.</p>
+<tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> requests they MUST return FAIL.</p>
+<p>Calls to either <tt class="docutils literal"><span class="pre">SplitControl.start()</span></tt> when the device is starting
+or <tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> while the device is stopping MUST return
+SUCCESS, with the anticipation that a corresponding
+<tt class="docutils literal"><span class="pre">SplitControl.startDone()</span></tt> or <tt class="docutils literal"><span class="pre">SplitControl.stopDone()</span></tt>
+will be signaled in the future.</p>
+<p>Calls to <cite>SplitControl.start()`</cite> when the device is started
+or <tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> while the device is stopped MUST
+return EALREADY, indicating that the device is already in that
+state. The corresponding completion event (startDone for start
+or stopDone for stop) MUST NOT be signaled.</p>
+<p>Calls to <cite>SplitControl.start()`</cite> when the device is stopping or
+<tt class="docutils literal"><span class="pre">SplitControl.stop()</span></tt> while the device is starting MUST return
+EBUSY, indicating that the device is busy performing a differnet
+operation. The correspodning completion event (startDone for start or
+stopDone for stop) MUST NOT be signaled.</p>
<table border="1" class="docutils">
<colgroup>
<col width="34%" />
<col width="15%" />
</colgroup>
<thead valign="bottom">
-<tr><th class="head">Call</th>
-<th class="head">Device On</th>
-<th class="head">Device Off</th>
-<th class="head">Starting</th>
-<th class="head">Stopping</th>
+<tr><th>Call</th>
+<th>Device On</th>
+<th>Device Off</th>
+<th>Starting</th>
+<th>Stopping</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>SplitControl.start()</td>
-<td>SUCCESS</td>
+<td>EALREADY</td>
<td>SUCCESS
FAIL</td>
<td>SUCCESS</td>
-<td>SUCCESS</td>
+<td>EBUSY</td>
</tr>
<tr><td>SplitControl.stop()</td>
<td>SUCCESS
FAIL</td>
-<td>SUCCESS</td>
-<td>SUCCESS</td>
+<td>EALREADY</td>
+<td>EBUSY</td>
<td>SUCCESS</td>
</tr>
<tr><td>operation</td>
}
</pre>
</div>
-<div class="section">
-<h2><a id="power-management-with-asyncstdcontrol" name="power-management-with-asyncstdcontrol">3.3 Power Management with <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt></a></h2>
+<div class="section" id="power-management-with-asyncstdcontrol">
+<h2><a name="power-management-with-asyncstdcontrol">3.3 Power Management with <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt></a></h2>
<p>The commands and the events of the <em>``StdControl``</em> and the <em>``SplitControl``</em>
interfaces are synchronous and can not be called from within
asynchronous code (such as interrupt service routines, etc.). For the
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">The <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt> interface should be provided whenever it might be
-necessary to allow a device to be powered on or off while running in
-async context. If it is anticipated that a device <em>will</em> not (or more
+necessary to allow a device to be powered on or off while running in
+async context. If it is anticipated that a device <em>will</em> not (or more
likely <em>should</em> not) be powered on or off while in asynchronous context,
-then the <tt class="docutils literal"><span class="pre">StdControl</span></tt> interface SHOULD be provided instead. Components
+then the <tt class="docutils literal"><span class="pre">StdControl</span></tt> interface SHOULD be provided instead. Components
that wish to power the device on or off from within async context would
-then be required to post a task before doing so. In practice,
-<tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt> is provided by low-level hardware resources, while
-<tt class="docutils literal"><span class="pre">StdControl</span></tt> is provided by higher level services built on top of these
+then be required to post a task before doing so. In practice,
+<tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt> is provided by low-level hardware resources, while
+<tt class="docutils literal"><span class="pre">StdControl</span></tt> is provided by higher level services built on top of these
resources.</p>
</div>
</div>
</div>
-<div class="section">
-<h1><a id="implicit-power-management" name="implicit-power-management">4. Implicit Power Management</a></h1>
-<p>While the <em>explicit power management</em> model provides the basic means
-for controlling the power state of a device, it is void of any
-policy about when, or how the power state of the device should be changed.
+<div class="section" id="implicit-power-management">
+<h1><a name="implicit-power-management">4. Implicit Power Management</a></h1>
+<p>While explicit power management provides the mechanism for changing
+power states, it does not specify a policy.
This does not represent a large problem for the simple case
-of <em>dedicated</em> devices, but can become crucial for non-trivial cases
-involving complex interdependencies between devices controlled by multiple
+of <em>dedicated</em> devices, but can become crucial for non-trivial cases
+involving complex interdependencies between devices controlled by multiple
clients.</p>
-<p>For example, if component <em>A</em> is a client of both component <em>B</em>
+<p>For example, if component <em>A</em> is a client of both component <em>B</em>
and component <em>C</em>, what happens with <em>B</em> and <em>C</em> if
<tt class="docutils literal"><span class="pre">StdControl.stop()</span></tt> is called on component <em>A</em> ? Should components
-<em>B</em> and <em>C</em> also be stopped? What about the reverse case where both
-<em>B</em> and <em>C</em> are clients of the single shared component, <em>A</em>? If
-devices <em>B</em> and <em>C</em> are shut off, should <em>A</em> be shut off as well?
+<em>B</em> and <em>C</em> also be stopped? What about the reverse case where both
+<em>B</em> and <em>C</em> are clients of the single shared component, <em>A</em>? If
+devices <em>B</em> and <em>C</em> are shut off, should <em>A</em> be shut off as well?
How can one decide when it is appropriate to cascade such powerup
and powerdown requests?</p>
<p>The complex nature of the problem is evident from the number of
unexpected behaviors in TinyOS 1.x involving <tt class="docutils literal"><span class="pre">StdControl</span></tt>. On several
platforms, one of the SPI buses is shared between the radio and the
flash device. On some of them, issuing <tt class="docutils literal"><span class="pre">StdControl.stop()</span></tt> on the
-radio results in a series of cascaded calls that result in SPI bus
-becoming disabled, rendering the communication with the flash impossible.
-Of course, the right policy would involve tracking the clients of the
-SPI bus and powering it off only once both the radio and the flash
+radio results in a series of cascaded calls that result in SPI bus
+becoming disabled, rendering the communication with the flash impossible.
+Of course, the right policy would involve tracking the clients of the
+SPI bus and powering it off only once both the radio and the flash
devices were no longer using it. Conversely, the SPI bus should be
powered on whenever there is at least one active client.</p>
-<p>The selection of the right power management policy to use is a complex
-task that depends on the nature of the devices in use, their
-interdependency, as well as on any specific application requirements.
-For cases when some of these features are known a-priori or are
-restricted in some sense, it is preferable that the system provide
-architectural support for enforcing a meaningful <em>default</em> power-management
-policy instead of passing that task on to the application programmer to be
+<p>The selection of the right power management policy to use is a complex
+task that depends on the nature of the devices in use, their
+interdependency, as well as on any specific application requirements.
+For cases when some of these features are known a-priori or are
+restricted in some sense, it is preferable that the system provide
+architectural support for enforcing a meaningful <em>default</em> power-management
+policy instead of passing that task on to the application programmer to be
solved on a case-by-case basis.</p>
-<div class="section">
-<h2><a id="power-management-policies" name="power-management-policies">4.1. Power Management Policies</a></h2>
-<p>Just as generic arbiters are offered in TinyOS 2.x to provide the arbitration
-functionality required by shared resources, generic power management policies are
-also offered to allow the power management of non-virtualised devices to
-be automatically control.</p>
-<p>Through the use of the arbiter components described in <a class="citation-reference" href="#tep108" id="id6" name="id6">[TEP108]</a>, device
-drivers implemented as shared resources provide the type of restricted
-resource interdependency where default power-management policies can be offered.
-The shared resource class defined in Section 2.3 of <a class="citation-reference" href="#tep108" id="id7" name="id7">[TEP108]</a>, provides a
-well defined component interdependency, where a single resource is shared
-among multiple clients. This relationship enables the definition of
-default power-management policies that can be used to automatically power
-the resource on and off.</p>
+<div class="section" id="power-management-policies">
+<h2><a name="power-management-policies">4.1. Power Management Policies</a></h2>
+<p>Just as generic arbiters are offered in TinyOS 2.x to provide the
+arbitration functionality required by shared resources, generic power
+management policies are also offered to allow the power management of
+non-virtualised devices to be automatically control.</p>
+<p>Through the use of the arbiter components described in <a class="citation-reference" href="#tep108" id="id6" name="id6">[TEP108]</a>,
+device drivers implemented as shared resources provide the type of
+restricted resource interdependency where default power-management
+policies can be offered. The shared resource class defined in Section
+2.3 of <a class="citation-reference" href="#tep108" id="id7" name="id7">[TEP108]</a>, provides a well defined component interdependency,
+where a single resource is shared among multiple clients. This
+relationship enables the definition of default power-management
+policies that can be used to automatically power the resource on and
+off.</p>
<p>The <em>Power Manager</em> component implementing one of these polices acts as
the <em>default owner</em> of the shared resource device and interacts with it
through the use of the ResourceDefaultOwner interface:</p>
<tt class="docutils literal"><span class="pre">ResourceDefaultOwner.granted()</span></tt> event to be signaled in order to
gain ownership over the resource device.</p>
<p>Once it owns the device, the <em>Power Manager</em> is free to execute its
-power-management policy using the StdControl-like interface provided by the
-underlying resource. Different power managers can implement different
+power-management policy using the StdControl-like interface provided by the
+underlying resource. Different power managers can implement different
policies. In the simplest case, this would involve an immediate power-down
-via one of the <tt class="docutils literal"><span class="pre">stop()</span></tt> commands. When the power-state transition
-involves non-negligible costs in terms of wake-up latency or power
-consumption, the <em>PowerManager</em> might revert to a more intelligent
-strategy that tries to reduce these effects. As pointed out in the
-introduction, one such strategy might involve the use of a timer to defer
-the power-down of the resource to some later point in time, giving any
-resource clients a window of opportunity to put in requests before the
+via one of the <tt class="docutils literal"><span class="pre">stop()</span></tt> commands. When the power-state transition
+involves non-negligible costs in terms of wake-up latency or power
+consumption, the <em>PowerManager</em> might revert to a more intelligent
+strategy that tries to reduce these effects. As pointed out in the
+introduction, one such strategy might involve the use of a timer to defer
+the power-down of the resource to some later point in time, giving any
+resource clients a window of opportunity to put in requests before the
device is fully shut down.</p>
-<p>Regardless of the power management policy in use, the <em>Power Manager</em>
-remains owner of the resource as long as the resource is not requested
+<p>Regardless of the power management policy in use, the <em>Power Manager</em>
+remains owner of the resource as long as the resource is not requested
by one of its clients. Whenever a client puts in a request, the
-<em>Power Manager</em> will receive a <tt class="docutils literal"><span class="pre">ResourceDefaultOwner.requested()</span></tt> event
-(or <tt class="docutils literal"><span class="pre">immediateRequested()</span></tt> event) from the arbiter it is associated with.
-Upon receiving this event, the <em>Power Manager</em> MUST power up the
+<em>Power Manager</em> will receive a <tt class="docutils literal"><span class="pre">ResourceDefaultOwner.requested()</span></tt> event
+(or <tt class="docutils literal"><span class="pre">immediateRequested()</span></tt> event) from the arbiter it is associated with.
+Upon receiving this event, the <em>Power Manager</em> MUST power up the
resource through the StdControl-like interface provided by the lower level
abstraction of the physical device. The <em>Power Manager</em> SHOULD release the
ownership of the resource (using the <tt class="docutils literal"><span class="pre">ResourceDefaultOwner.release()</span></tt>
-command) but MUST wait until after the resource has been fully powered on
+command) but MUST wait until after the resource has been fully powered on
before doing so.</p>
<p>Modeling devices as shared resources and allowing them to be
controlled in the way described here, solves the problems outlined in
events answers the question of when. As long as the resource at
the bottom of a large set of nested resource clients has been fully released,
the power mananger will be able to power down the resource appropriately.</p>
-<p>Using the model described above, a resource that uses one of these policies
+<p>Using the model described above, a resource that uses one of these policies
according to the <em>implicitly power management</em> model could be built as shown below:</p>
<pre class="literal-block">
module MyFlashP {
}
implementation {
...
-}
+}
generic module PowerManagerC(uint8_t POWERDOWN_DELAY) {
provides {
, MyFlashP;
Init = MyFlashP;
- Resource = FcfsArbiter;
+ Resource = FcfsArbiter;
FlashCommands = MyFlashP;
PowerManagerC.ResourceDefaultUser -> FcfsArbiter;
PowerManagerC.SplitControl -> MyFlashP;
-
+
}
</pre>
<p>This example implementation is built out of three components. The
components, as well as an arbiter component for managing shared clients
of the device. Notice how the <em>Power Manager</em> is wired to both the
<tt class="docutils literal"><span class="pre">ResourceDefaultUser</span></tt> interface provided by the arbiter, and the
-<tt class="docutils literal"><span class="pre">SplitControl</span></tt> interface provided by the flash. All clients of this flash
+<tt class="docutils literal"><span class="pre">SplitControl</span></tt> interface provided by the flash. All clients of this flash
device are directly connected to the resource interface provided by
the arbiter. As outlined above, the <tt class="docutils literal"><span class="pre">PowerManagerC</span></tt> component will use
-the events signaled through the <tt class="docutils literal"><span class="pre">ResourceDefaultUser</span></tt> interface to determine
+the events signaled through the <tt class="docutils literal"><span class="pre">ResourceDefaultUser</span></tt> interface to determine
when to make calls to power the device up and power it down through
the <tt class="docutils literal"><span class="pre">SplitControl</span></tt> interface.</p>
</div>
-<div class="section">
-<h2><a id="example-power-managers-powermanagerc-and-deferredpowermanagerc" name="example-power-managers-powermanagerc-and-deferredpowermanagerc">4.2. Example Power Managers: PowerManagerC and DeferredPowerManagerC</a></h2>
+<div class="section" id="example-power-managers-powermanagerc-and-deferredpowermanagerc">
+<h2><a name="example-power-managers-powermanagerc-and-deferredpowermanagerc">4.2. Example Power Managers: PowerManagerC and DeferredPowerManagerC</a></h2>
<p>TinyOS 2.x currently has two default power management policies
-that it provides. These policies are implemented by the various
-components located under tinyos-2.x/lib/power. The first policy
+that it provides. These policies are implemented by the various
+components located under tinyos-2.x/lib/power. The first policy
is implemented using an <em>immediate</em> power control scheme, whereby
devices are powered on and off immediately after they have been
requested and released. The second policy is implemented using
-a <em>deferred</em> power control scheme, whereby devices are powered
+a <em>deferred</em> power control scheme, whereby devices are powered
on immediately after being requested, but powered off after
some small delay from being released.</p>
-<p>Each policy has three different implementations for use by each of
+<p>Each policy has three different implementations for use by each of
the <tt class="docutils literal"><span class="pre">StdControl</span></tt>, <tt class="docutils literal"><span class="pre">SplitControl</span></tt>, and <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt>
interfaces.</p>
<p>For reference, each of the available components are listed below</p>
</dl>
</div>
</div>
-<div class="section">
-<h1><a id="author-s-address" name="author-s-address">5. Author's Address</a></h1>
+<div class="section" id="author-s-address">
+<h1><a name="author-s-address">5. Author's Address</a></h1>
<div class="line-block">
<div class="line">Kevin Klues</div>
<div class="line">503 Bryan Hall</div>
<div class="line">Stanford, CA 94305-9030</div>
<div class="line"><br /></div>
<div class="line">phone - +1 650 725 9046</div>
-<div class="line">email - <a class="reference" href="mailto:pal@cs.stanford.edu">pal@cs.stanford.edu</a></div>
+<div class="line">email - <a class="reference" href="mailto:pal@cs.stanford.edu">pal@cs.stanford.edu</a> </div>
</div>
</div>
-<div class="section">
-<h1><a id="citations" name="citations">6. Citations</a></h1>
+<div class="section" id="citations">
+<h1><a name="citations">6. Citations</a></h1>
<table class="docutils citation" frame="void" id="tep102" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
projects / tinyos-2.x.git / blobdiff