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<title>Microcontroller Power Management</title>
<meta name="author" content="Robert Szewczyk, Philip Levis, Martin Turon, Lama Nachman, Philip Buonadonna, Vlado Handziski" />
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<td>Robert Szewczyk, Philip Levis, Martin Turon, Lama Nachman, Philip Buonadonna, Vlado Handziski</td></tr>
<tr class="field"><th class="docinfo-name">Draft-Created:</th><td class="field-body">19-Sep-2005</td>
</tr>
-<tr class="field"><th class="docinfo-name">Draft-Version:</th><td class="field-body">1.2</td>
+<tr class="field"><th class="docinfo-name">Draft-Version:</th><td class="field-body">1.8</td>
</tr>
-<tr class="field"><th class="docinfo-name">Draft-Modified:</th><td class="field-body">2006-07-12</td>
+<tr class="field"><th class="docinfo-name">Draft-Modified:</th><td class="field-body">2009-07-07</td>
</tr>
<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>
</div>
<div class="section">
<h1><a id="background" name="background">2. Background</a></h1>
-<p>The TinyOS scheduler[_tep106] puts a processor into a sleep state when
+<p>The TinyOS scheduler[<a class="reference" href="#id3">2</a>] puts a processor into a sleep state when
the task queue is empty. However, processors can have a spectrum of
power states. For example, the MSP430 has one active mode (issuing
instructions) and five low-power modes. The low power modes range from
higher-level components. While wakeup latency is not a significant
issue on very low power microcontrollers, such as the Atmega128 and
MSP430, more powerful processors, such as the Xscale family (the basis
-of platforms such as the imote2) can power states with wakeup
+of platforms such as the imote2) can have power states with wakeup
latencies as large as 5ms. For some application domains, this latency
could be a serious issue. Higher level components therefore need a way
to give the TinyOS microcontroller power manager information on their
higher level components to introduce additional requirements, if
needed.</p>
<p>These three mechanisms all operate in the TinyOS core scheduling loop,
-described in TEP 106: Schedulers and Tasks[_tep106]. This loop is
+described in TEP 106: Schedulers and Tasks[<a class="reference" href="#id3">2</a>]. This loop is
called from the boot sequence, which is described in TEP 107: Boot
-Sequence[_tep107]. The command in question is
-<tt class="docutils literal"><span class="pre">Scheduler.runNextTask()</span></tt>, when its sleep parameter is TRUE (i.e.,
-<tt class="docutils literal"><span class="pre">call</span> <span class="pre">Scheduler.runNextTask(TRUE)</span></tt>).</p>
+Sequence[<a class="reference" href="#id4">3</a>]. The command in question is
+<tt class="docutils literal"><span class="pre">Scheduler.taskLoop()</span></tt>, when microcontroller sleeping is enabled.</p>
<p>If this command is called when the task queue is empty, the TinyOS
scheduler puts the microcontroller to sleep. It does so through
the <tt class="docutils literal"><span class="pre">McuSleep</span></tt> interface:</p>
<div class="section">
<h1><a id="the-dirty-bit" name="the-dirty-bit">3.1 The Dirty Bit</a></h1>
<p>Whenever a Hardware Presentation Layer (HPL, see TEP 2: Hardware
-Abstraction Architecture[_tep2]) component changes an aspect of
+Abstraction Architecture[<a class="reference" href="#id2">1</a>]) component changes an aspect of
hardware configuration that might change the possible low power state
of the microcontroller, it MUST call McuPowerState.update(). This is
the first power management mechanism, a <em>dirty bit</em>. If
variable. Wiring arbitrarily to this command is an easy way to cause
TinyOS to behave badly. The presence of a combine function for
mcu_power_t means that this command can have fan-out calls.</p>
+<p>Section 5 describes one example use of McuPowerOverride, in the
+timer stack for the Atmega128 microcontroller family.</p>
+<p>As part of power state override, a platform MUST define the enum
+TOS_SLEEP_NONE in its hardware.h file. This enum defines the highest
+power state of the platform's microcontroller in a chip-independent
+way. If a component wires to McuPowerOverride and returns TOS_SLEEP_NONE,
+this will cause TinyOS to never put the microcontroller into a power
+saving state. This enum allows a component to prevent sleep in a
+platform-independent way.</p>
</div>
<div class="section">
<h1><a id="peripherals-and-subsystems" name="peripherals-and-subsystems">4. Peripherals and Subsystems</a></h1>
<p>At the HIL level, TinyOS subsystems generally have a simple,
imperative power management interface. Depending on the latencies
-involved, this interface is either <tt class="docutils literal"><span class="pre">StdControl</span></tt> or <tt class="docutils literal"><span class="pre">SplitControl</span></tt>.
+involved, this interface is either <tt class="docutils literal"><span class="pre">StdControl</span></tt>, <tt class="docutils literal"><span class="pre">SplitControl</span></tt>,
+or <tt class="docutils literal"><span class="pre">AsyncStdControl</span></tt>.
These interfaces are imperative in that when any component calls
-<tt class="docutils literal"><span class="pre">StdControl.stop</span></tt> on another component, it causes the subsystem that
+<tt class="docutils literal"><span class="pre">stop</span></tt> on another component, it causes the subsystem that
component represents to enter an inactive, low-power state.</p>
<p>From the perspective of MCU power management, this transition causes a
change in status and control registers (e.g., a clock is
disabled). Following the requirements in 3.1, the MCU power management
subsystem will be notified of a significant change and act
-appropriately when the system next goes to sleep.</p>
-<p>These imperative appraoches are flexible and powerful, but are also
-very error prone, partially due to their deep semantics. For example,
-depending on the circumstances, an application calling StdControl.stop
-on a routing layer may or may not also want to turn off the underlying
-radio. StdControl and SplitControl provide a <em>mechanism</em> to control
-subsystem power states, but no real <em>policy</em> for arbitrating
-conflicting requirements from components built on top of them.</p>
-<p>Service distributions (described in TEP 110[_tep110]) are responsible
-for providing policies on top of these low-level mechanisms. OSKI, for
-example, the sample distribution described in TEP 110, uses an
-OR-policy: a subsystem is active if any of its clients want it active,
-and inactive iff all of its clients want it inactive. Other
-distributions can provide alternative power management policies in top
-of the basic HIL mechanisms.</p>
+appropriately when the system next goes to sleep. TEP 115[<a class="reference" href="#id6">5</a>]
+describes the power management of non-virtualized devices in
+greater detail, and TEP 108[<a class="reference" href="#id5">4</a>] describes how TinyOS can automatically
+include power management into shared non-virtualized devices.</p>
+</div>
+<div class="section">
+<h1><a id="implementation" name="implementation">5. Implementation</a></h1>
+<p>An implementation of McuSleepC can be found in <tt class="docutils literal"><span class="pre">tinyos-2.x/tos/chips/atm128</span></tt>,
+<tt class="docutils literal"><span class="pre">tinyos-2.x/tos/chips/msp430</span></tt>, and <tt class="docutils literal"><span class="pre">tinyos-2.x/tos/chips/px27ax</span></tt>.</p>
+<p>An example use of McuPowerOverride can be found in the atmega128 timer
+system. Because some low-power states have much longer wakeup latencies than
+others, the timer system does not allow long latencies if it has a timer
+that is going to fire soon. The implementation can be found in
+<tt class="docutils literal"><span class="pre">tinyos-2.x/tos/chips/atm128/timer/HplAtm128Timer0AsyncP.nc</span></tt>, and
+<tt class="docutils literal"><span class="pre">tinyos-2.x/tos/chips/atm128/timer/HplAtm128Timer0AsyncC.nc</span></tt> automatically
+wires it to McuSleepC if it is included.</p>
+<p>For the atmega128 microcontroller, TOS_SLEEP_NONE is the "idle" power
+state.</p>
+<p>A second example use of McuPowerOverride is in the msp430 timer system.
+By default, the msp430 lowest power state is LPM4, which does not keep
+clocks enabled. If <tt class="docutils literal"><span class="pre">tinyos-2.x/tos/chips/msp430/timer/Msp430ClockC.nc''</span>
+<span class="pre">is</span> <span class="pre">included</span> <span class="pre">in</span> <span class="pre">the</span> <span class="pre">component</span> <span class="pre">graph,</span> <span class="pre">however,</span> <span class="pre">this</span> <span class="pre">configuration</span> <span class="pre">wires</span>
+<span class="pre">the</span> <span class="pre">McuPowerOverride</span> <span class="pre">of</span> <span class="pre">``tinyos-2.x/tos/chips/msp430/timer/Msp430ClockP.nc</span></tt>
+to McuSleepC. This implemementation of McuPowerOverride raises the lowest
+power state to LPM3, which keeps clocks enabled.</p>
+<p>For msp430 microcontrollers, TOS_SLEEP_NONE is the "active" power state.</p>
</div>
<div class="section">
-<h1><a id="author-s-address" name="author-s-address">5. Author's Address</a></h1>
+<h1><a id="author-s-address" name="author-s-address">6. Author's Address</a></h1>
<div class="line-block">
<div class="line">Robert Szewczyk</div>
<div class="line">Moteiv Corporation</div>
</div>
<div class="section">
<h1><a id="citations" name="citations">6. Citations</a></h1>
-<table class="docutils citation" frame="void" id="tep106" rules="none">
+<table class="docutils footnote" frame="void" id="id2" rules="none">
+<colgroup><col class="label" /><col /></colgroup>
+<tbody valign="top">
+<tr><td class="label"><a name="id2">[1]</a></td><td>TEP 2: Hardware Abstraction Architecture</td></tr>
+</tbody>
+</table>
+<table class="docutils footnote" frame="void" id="id3" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
-<tr><td class="label"><a name="tep106">[tep106]</a></td><td>TEP 106: Schedulers and Tasks.</td></tr>
+<tr><td class="label"><a name="id3">[2]</a></td><td>TEP 106: Schedulers and Tasks.</td></tr>
</tbody>
</table>
-<table class="docutils citation" frame="void" id="tep107" rules="none">
+<table class="docutils footnote" frame="void" id="id4" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
-<tr><td class="label"><a name="tep107">[tep107]</a></td><td>TEP 107: TinyOS 2.x Boot Sequence.</td></tr>
+<tr><td class="label"><a name="id4">[3]</a></td><td>TEP 107: TinyOS 2.x Boot Sequence.</td></tr>
</tbody>
</table>
-<table class="docutils citation" frame="void" id="tep110" rules="none">
+<table class="docutils footnote" frame="void" id="id5" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
-<tr><td class="label"><a name="tep110">[tep110]</a></td><td>TEP 110: Service Distributions.</td></tr>
+<tr><td class="label"><a name="id5">[4]</a></td><td>TEP 108: Resource Arbitration</td></tr>
</tbody>
</table>
-<table class="docutils citation" frame="void" id="tep2" rules="none">
+<table class="docutils footnote" frame="void" id="id6" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
-<tr><td class="label"><a name="tep2">[tep2]</a></td><td>TEP 2: Hardware Abstraction Architecture.</td></tr>
+<tr><td class="label"><a name="id6">[5]</a></td><td>TEP 115: Power Management of Non-Virtualised Devices</td></tr>
</tbody>
</table>
</div>
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