boot sequence - tinyos documentation wiki.htm

从官方网站上下载tinyos2.0的学习指南

<P>A common issue in initialization code is dependencies between different parts 
of the system. These are handled in three ways in TinyOS: </P>
<UL>
  <LI>Hardware-specific initialization issues are handled directly by each 
  platform's <CODE>PlatformC</CODE> component. 
  <LI>System services (e.g., the timer, the radio) are typically written to be 
  independently initializable. For instance, a radio that uses a timer does not 
  setup the timer at radio initialisation time, rather it defers that action 
  until the radio is started. In other words, initialisation is used to setup 
  software state, and hardware state wholly owned by the service. 
  <LI>When a service is split into several components, the <CODE>Init</CODE> 
  interface for one of these components may well call <CODE>Init</CODE> (and 
  other) interfaces of the other components forming the service, if a specific 
  order is needed. </LI></UL><A 
name=Signal_that_the_boot_process_has_completed.></A>
<H2><SPAN class=mw-headline>Signal that the boot process has 
completed.</SPAN></H2>
<P>Once all initialization has completed, <CODE>MainC</CODE>'s 
<CODE>Boot.booted()</CODE> event is signaled. Components are now free to call 
<CODE>start()</CODE> and other commands on any components they are using. Recall 
that in the <CODE>Blink</CODE> application, the timers were started from the 
<CODE>booted()</CODE> event. This <CODE>booted</CODE> event is TinyOS's analogue 
of <CODE>main</CODE> in a Unix application. </P><A 
name=Run_the_scheduler_loop.></A>
<H2><SPAN class=mw-headline>Run the scheduler loop.</SPAN></H2>
<P>Once the application has been informed that the system as booted and started 
needed services, TinyOS enters its core scheduling loop. The scheduler runs as 
long as there are tasks on the queue. As soon as it detects an empty queue, the 
scheduler puts the microcontroller into the lowest power state allowed by the 
active hardware resources. For example, only having timers running usually 
allows a lower power state than peripheral buses like the UART. <A 
class="external text" 
title=http://www.tinyos.net/tinyos-2.x/doc/html/tep112.html 
href="http://www.tinyos.net/tinyos-2.x/doc/html/tep112.html" rel=nofollow>TEP 
112</A> describes in detail how this process works. </P>
<P>The processor goes to sleep until it handles an interrupt. When an interrupt 
arrives, the MCU exits its sleep state and runs the interrupt handler. This 
causes the scheduler loop to restart. If the interrupt handler posted one or 
more tasks, the scheduler runs tasks until the task queue and then returns to 
sleep. </P><A name=Boot_and_SoftwareInit></A>
<H1><SPAN class=mw-headline>Boot and SoftwareInit</SPAN></H1>
<P>From the perspective of an application or high-level services, the two 
important interfaces in the boot sequence are those which MainC exports: Boot 
and SoftwareInit. Boot is typically only handled by the top-level application: 
it starts services like timers or the radio. SoftwareInit, in contrast, touches 
many difference parts of the system. If a component needs code that runs once to 
initialize its state or configuration, then it can wire to SoftwareInit. </P>
<P>Typically, service components that require intialization wire themselves to 
SoftwareInit rather than depend on the application writer to do so. When an 
application developer is writing a large, complex system, keeping track of all 
of the initialization routines can be difficult, and debugging when one is not 
being called can be very difficult. To prevent bugs and simplify application 
development, services typically use <I>auto-wiring</I>. </P>
<P>The term auto-wiring refers to when a component automatically wires its 
dependencies rather than export them for the application writer to resolve. In 
this case, rather than provide the Init interface, a service component wires its 
Init interface to RealMainC. For example, <TT>PoolC</TT> is a generic memory 
pool abstraction that allows you to declare a collection of memory objects for 
dynamic allocation. Underneath, its implementation (<TT>PoolP</TT>) needs to 
initialize its data structures. Given that this must happen for the component to 
operate properly, an application writer shouldn't have to worry about it. So the 
PoolC component instantiates a PoolP and wires it to MainC.SoftwareInit: </P><PRE>generic configuration PoolC(typedef pool_t, uint8_t POOL_SIZE) {
  provides interface Pool;
}

implementation {
  components MainC, new PoolP(pool_t, POOL_SIZE);

  MainC.SoftwareInit -&gt; PoolP;
  Pool = PoolP;
}
</PRE>
<P>In practice, this means that when MainP calls SoftwareInit.init, it calls 
Init.init on a large number of components. In a typical large application, the 
initialization sequence might involve as many as thirty components. But the 
application developer doesn't have to worry about this: properly written 
components take care of it automatically. </P><A name=Related_Documentation></A>
<H1><SPAN class=mw-headline>Related Documentation</SPAN></H1>
<UL>
  <LI><A class="external text" 
  title=http://www.tinyos.net/tinyos-2.x/doc/html/tep106.html 
  href="http://www.tinyos.net/tinyos-2.x/doc/html/tep106.html" rel=nofollow>TEP 
  106: Schedulers and Tasks</A> 
  <LI><A class="external text" 
  title=http://www.tinyos.net/tinyos-2.x/doc/html/tep107.html 
  href="http://www.tinyos.net/tinyos-2.x/doc/html/tep107.html" rel=nofollow>TEP 
  107: Boot Sequence</A> </LI></UL>
<P><B>Programming Hint 8:</B> In the top-level configuration of a software 
abstraction, auto-wire Init to MainC. This removes the burden of wiring Init 
from the programmer, which removes unnecessary work from the boot sequence and 
removes the possibility of bugs from forgetting to wire. From <A 
class="external text" 
title=http://www.tinyos.net/tinyos-2.x/doc/pdf/tinyos-programming.pdf 
href="http://www.tinyos.net/tinyos-2.x/doc/pdf/tinyos-programming.pdf" 
rel=nofollow><I>TinyOS Programming</I></A><BR></P>
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