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<!doctype html public "-//w3c//dtd html 4.0 transitional//en"><html><head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <meta name="GENERATOR" content="Mozilla/4.78 [en] (X11; U; Linux 2.4.7-10 i686) [Netscape]"> <title>Lesson 2: Event-Driven Sensor Acquisition</title><!-- mdw@eecs.harvard.edu - modified to fix StdControl references in Sounder --></head><body bgcolor="#F8F8FF" link="#005BB7" vlink="#005BB7"> <table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="100%" hspace="4" ><tr BGCOLOR="#E0E0FF"><td WIDTH="100%"><b><font face="tahoma,arial,helvetica"><font size=-1>Lesson2: Event-Driven Sensor Acquisition</font></font></b><p><font face="tahoma,arial,helvetica">Last updated 9 September 2003</font></td></tr></table><p>This lesson demonstrates a simple sensor application that takes lightintensity readings (from the sensor board's photo sensor on Mica motes orfrom the onboard temperature sensor on Telos) and displaysthose readings on the LEDs. This is based on the <tt>Sense</tt> application,found in <tt><a href="../../apps/Sense">apps/Sense</a></tt>. This is avery simple application that reads a value from the light sensor and displaysthe lower 3 bits of the value on the LEDs. The application configurationis found in<tt>Sense.nc</tt> and the implementation module in <tt>SenseM.nc</tt>.<table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="100%" hspace="4" ><tr BGCOLOR="#E0E0FF"><td WIDTH="100%"><b><nobr><font face="arial,helvetica">The SenseM.nc component</font></nobr></b></td></tr></table><p>Let's first look at the top portion of <tt>SenseM.nc</tt>:<center><table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="80%" hspace="4" ><tr BGCOLOR="#E0E0E0"><td WIDTH="100%"><b>SenseM.nc</b><pre>module SenseM { provides { interface StdControl; } uses { interface Timer; interface ADC; interface StdControl as ADCControl; interface Leds; }}// Implementation not shown ...</pre></td></tr></table></center><p>Like <tt>BlinkM</tt>, this component provides the <tt>StdControl</tt>interface and uses <tt>Timer</tt> and <tt>Leds</tt>. It also uses two moreinterfaces: <tt>ADC</tt>, which is used to access data from the analogue-to-digitalconverter, and <tt>StdControl</tt>, which is used to initialize the ADCcomponent.<p>This application uses a new component, <tt>TimerC</tt>, in place of<tt>SingleTimer</tt>.The reason is that <tt>TimerC</tt> allows multiple instance of timers,while <tt>SingleTimer</tt> only provides a single one that only one componentcan use. We'll discuss more on <tt>Timer</tt> a bit later.<p>Note the line<pre> interface StdControl as ADCControl;</pre>This is saying that this component uses the <tt>StdControl</tt> interfacebut gives the <b>interface instance</b> the name<tt>ADCControl</tt>. Inthis way a component can require multiple instances of the same interface,but give them different names. For example, a component might need to usethe <tt>StdControl</tt> interface to control both the ADC and the soundercomponents. In this case we might say:<pre> interface StdControl as ADCControl; interface StdControl as SounderControl;</pre>The configuration that uses this module will be responsible for wiringeach interface instance to some actual implementation.<p>One related note: if you don't provide an interface instance name thenthe instance is named the same as the interface. That is, the line<pre> interface ADC;</pre>is just shorthand for<pre> interface ADC as ADC;</pre>Take a look at the <tt>StdControl</tt> and <tt>ADC</tt> interfaces (bothin tos/interfaces). You'll see that<tt><a href="../../tos/interfaces/StdControl.nc">StdControl</a></tt>is used to initialize and power a component (usually a piece of physicalhardware) and <tt><a href="../../tos/interfaces/ADC.nc">ADC</a></tt> isused to get data from an ADC channel. <tt>ADC</tt> signals an event, <tt>dataReady()</tt>,when data is ready on the channel. Notice the <b>async</b> keyword is usedin the ADC interface. This is declaring the commands and events as asynchronouscode, i.e., code which can run in response to a hardware interrupt.<p>Open the file <tt><a href="../../apps/Sense/SenseM.nc">apps/Sense/SenseM.nc</a></tt>. You'll see the code simply calls<tt>ADC.getData()</tt> each time<tt>Timer.fired()</tt>is signaled. Likewise, when <tt>ADC.dataReady()</tt> is signaled, theinternal function <tt>display()</tt> is invoked, which sets the LEDs tothe low-order bits of the ADC value.<p>Notice the use of the function <tt>rcombine()</tt> in the implementationof <tt>StdControl.init()</tt>.<pre> return rcombine(call ADCControl.init(), call Leds.init());</pre>The function <tt>rcombine()</tt> is a special nesC combining function whichreturns the logical-and of two commands who result type is result_t.<br> <table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="100%" hspace="4" ><tr BGCOLOR="#E0E0FF"><td WIDTH="100%"><b><nobr><font face="arial,helvetica">The Sense.nc configuration</font></nobr></b></td></tr></table><p>At this point you should be wondering, "how does the <tt>Sense</tt>application know that the ADC channel should access the light sensor?"This is exactly what the <tt>Sense.nc</tt> configuration wires up for us.<center><table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="80%" hspace="4" ><tr BGCOLOR="#E0E0E0"><td WIDTH="100%"><b>Sense.nc</b><pre>configuration Sense { // this module does not provide any interface}implementation{ components Main, SenseM, LedsC, TimerC, DemoSensorC as Sensor; Main.StdControl -> TimerC; Main.StdControl -> DemoSensorC; Main.StdControl -> SenseM; SenseM.ADC -> Sensor; SenseM.ADCControl -> Sensor; SenseM.Leds -> LedsC; SenseM.Timer -> TimerC.Timer[unique("Timer")];}</pre></td></tr></table></center><p>Most of this should be familiar from <tt>Blink</tt>. We're wiring upthe<tt>Main.StdControl</tt> to <tt>SenseM.StdControl</tt>, as before.The<tt>Leds</tt> wirings is also similar to <tt>Blink</tt>, and we'lldiscuss<tt>Timer</tt> in a minute. The wiring for the ADC is:<pre> SenseM.ADC -> Sensor; SenseM.ADCControl -> Sensor;</pre>All we're doing is wiring up the <tt>ADC</tt> interface (used by<tt>SenseM</tt>)to a new component called <tt>DemoSensorC</tt>. Same goes for the <tt>ADCControl</tt>interface, which you'll recall is an instance of the <tt>StdControl</tt>interface used by<tt>SenseM</tt>.<p>Remember that<pre> SenseM.ADC -> Sensor;</pre>is just shorthand for<pre> SenseM.ADC -> Sensor.ADC;</pre>On the other hand,<pre> SenseM.ADControl -> Sensor;</pre>is <b>not shorthand</b> for<pre> SenseM.ADC -> Sensor.ADCControl;</pre>What's going on here? If you look at the <tt>DemoSensorC.nc</tt> component (foundin<tt>tos/sensorboards/micasb</tt>), you'll see that it provides boththe <tt>ADC</tt> and <tt>StdControl</tt> interfaces -- it doesn't havean interface called <tt>ADCControl</tt>. (<tt>ADCControl</tt> was justthe name that we gave to the instance of<tt>StdControl</tt> in the <tt>SenseM</tt>component.) Rather, the nesC compiler is smart enough to figure out thatbecause <tt>SenseM.ADCControl</tt> is <i>an instance of</i> the <tt>StdControl</tt>interface, that it needs to be wired up to<i>an instance of</i> the <tt>StdControl</tt>interface provided by <tt>DemoSensorC</tt>. (If <tt>DemoSensorC</tt> were to providetwo instances of<tt>StdControl</tt>, this would be an error because thewiring would be ambiguous.) In other words,<pre> SenseM.ADControl -> Sensor;</pre>is shorthand for<pre> SenseM.ADControl -> Sensor.StdControl;</pre>Whew!<br> <table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="100%" hspace="4" ><tr BGCOLOR="#E0E0FF"><td WIDTH="100%"><b><nobr><font face="arial,helvetica">Timer and parameterizedinterfaces</font></nobr></b></td></tr></table><p>Let's look at the line<pre> SenseM.Timer -> TimerC.Timer[unique("Timer")];</pre>This is introducing a new bit of syntax, called a <b>parameterized interface</b>.<p>A parameterized interface allows a component to provide<i>multipleinstances</i> of an interface that are parameterized by a runtime or compile-timevalue. Recall that it's possible for a component to provide multiple instancesof an interface and to give them different names, e.g.,<pre> provides { interface StdControl as fooControl; interface StdControl as barControl; }</pre>This is just a generalization of the same idea. The <tt>TimerC</tt> componentdeclares:<pre> provides interface Timer[uint8_t id];</pre>In other words, it provides 256 different instances of the<tt>Timer</tt>interface, one for each <tt>uint8_t</tt> value!<p>In this case, we want TinyOS applications to create and use multipletimers, each of which can be managed independently. For example, an applicationcomponent might need one timer to fire at a certain rate (say, once persecond) to gather sensor readings, while another component might need thea timer to fire at a different rate to manage radio transmission. By wiringthe <tt>Timer</tt> interface in each of these components to a separateinstance of the <tt>Timer</tt> interface provided by <tt>TimerC</tt>, eachcomponent can effectively get its own "private" timer.<p>When we say <tt>TimerC.Timer[someval]</tt>, we are specifying that<tt>BlinkM.Timer</tt>should be wired to the instance of the<tt>Timer</tt> interface specifiedby the value (<tt>someval</tt>) in the square brackets. This can be any8-bit positive number. If we were to specify a particular value here, suchas 38 or 42, we might accidentally conflict with the timer being used byanother component (if that component used the same value in the brackets).So, we use the compile-time constant function <tt>unique()</tt>, whichgenerates a unique 8-bit identifier from the string given as an argument.Here,<pre> unique("Timer")</pre>generates a unique 8-bit number from a set corresponding to the string<tt>"Timer"</tt>.Therefore, Every component that uses <tt>unique("Timer")</tt> is guaranteedto get a <i>different</i> 8-bit value as long as the string used in theargument is the same. Note that if one component uses <tt>unique("Timer")</tt>and another uses<tt>unique("MyTimer")</tt>, they might get the <i>same</i>8-bit value. Therefore it's good practice to use the name of the parameterizedinterface as an argument to the <tt>unique()</tt> function. The compile-timeconstant function<tt></tt><p><tt> uniqueCount("Timer")</tt><p>will count the number of uses of <tt>unique("Timer"</tt>).<br> <table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="100%" hspace="4" ><tr BGCOLOR="#E0E0FF"><td WIDTH="100%"><b><nobr><font face="arial,helvetica">Running the Senseapplication</font></nobr></b></td></tr></table><p>As before, just do a <tt>make mica install</tt> in the <tt>Sense</tt>directory to compile and install the application on your mote. For Mica motes, you'll needa sensor board attached to the mote with a photo sensor. The Mica sensorboard, for example, snaps into place via the 51 pin connector. The typeof sensorboard is selected by the <tt>-board</tt> command line option to<tt>ncc</tt>.On the Mica mote, the default sensor board type is <tt>micasb</tt>. However,if you have an older ("basic") sensor board, you might need to pass inthe <tt>-board basicsb</tt> option to <tt>ncc</tt>. To do this, edit the<tt><a href="../../apps/Sense/Makefile">Makefile</a></tt>in the<tt>Sense</tt> directory and add the line<tt>SENSORBOARD=basicsb</tt>beforethe line that includes <tt>Makerules</tt>. The sensor boards supportedby TinyOS are represented by the directory names in <a href="../../tos/sensorboards">tos/sensorboards</a>.If you are using Telos motes, the temperature sensor is built into themicrocontroller and doesn't require a sensorboard or the <tt>-board</tt>command line option. <p>The operation of the sensor is a bit unusual. The ADC yields a10-bit digitized sample of the photo sensor. What we would like is forthe LEDs to be off when the node is in the light, and on when the nodeis in the dark. Here, we are looking at the upper three bits of this datacoming from the ADC, and inverting the value. Note the line:<pre> display(7 - ((data >> 7) & 0x7));</pre>in the <tt>ADC.dataReady()</tt> function of <tt>SenseM</tt>.<p>Note that when running the application you may really have to coverup the photo sensor pretty well to get it to respond - we'll admit thatthis is not the best application to really see the photo sensor at work!<br> <table BORDER=0 CELLSPACING=2 CELLPADDING=3 WIDTH="100%" hspace="4" ><tr BGCOLOR="#E0E0FF"><td WIDTH="100%"><b><nobr><font face="arial,helvetica">Exercises</font></nobr></b></td></tr></table><p><b>For Mica motes:</b>Extend the capability of the application by chirping the sensor board'ssounder when it is dark! The TinyOS component for the Sounder is locatedin <tt>tos/sensorboards/micasb/Sounder.nc</tt> and provides the<tt>StdControl</tt>interface. Modify <tt>SenseM.nc</tt> to add a<tt>StdControl</tt> as <tt>SounderControl</tt>,wiring it as appropriate in <tt>Sense.nc</tt>. Remember to call init()to initialize the Sounder component. To make the sounder turn on from SenseM.nc,call<tt>SounderControl.start()</tt>. To turn off the sounder, call<tt>SounderControl.stop()</tt>.Be sure to test this new application many times to annoy everyone sittingaround you.<p><hr><b><a href="lesson1.html">< Previous Lesson</a></b> |<b><a href="lesson3.html">NextLesson ></a></b> | <b><a href="index.html">Top</a></b></body></html><!-- LocalWords: TinyOS nesC nc async norace BlinkM FooM ncc SingleTimer Leds --><!-- LocalWords: LedsC StdControl tos init TimerC redOn redOff uint redToggle --><!-- LocalWords: metadata html nesdoc gcc exe avr objcopy srec uisp mib dprog --><!-- LocalWords: towards dapa xff ThinkPad dlpt Makelocal micasb Wshadow DDEF --><!-- LocalWords: finline fnesc cfile lm Atmel ATmega nesC's nesc SenseM --><!-- LocalWords: ADCControl SounderControl dataReady getData rcombine someval --><!-- LocalWords: ADControl fooControl barControl MyTimer uniqueCount basicsb --><!-- LocalWords: sensorboard Makerules sensorboards -->⌨️ 快捷键说明
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