storage - tinyos documentation wiki.htm

从官方网站上下载tinyos2.0的学习指南

application requirement. Logged data should not be lost if a system crashes. 
Logs can be either linear (stop logging when the volume is full) or circular 
(overwrite the least recently written data when the volume is full). </P>
<P>The TinyOS LogStorage abstraction supports these requirements. The log is 
record based: each call to LogWrite.append (see below) creates a new record. On 
failure (a crash or power cycle), the log only loses whole records from the end 
of the log. Additionally, once a circular log wraps around, log writes only lose 
whole records from the beginning of the log. </P>
<P>A demo application called <CODE>PacketParrot</CODE> shows how to use the 
<CODE>LogWrite</CODE> and <CODE>LogRead</CODE> abstractions. A node writes 
received packets to a circular log and retransmits the logged packets (or at 
least the parts of the packets above the AM layer) when power is cycled. </P>
<P>See <A class="external text" 
title=http://www.tinyos.net/tinyos-2.x/apps/tutorials/PacketParrot/ 
href="http://www.tinyos.net/tinyos-2.x/apps/tutorials/PacketParrot/" 
rel=nofollow><CODE>tinyos-2.x/apps/tutorials/PacketParrot/</CODE></A> for the 
accompanying code. </P>
<P>The application logs packets it receives from the radio to flash. On a 
subsequent power cycle, the application transmits any logged packets, erases the 
log, and then continues to log packets again. The red LED is on when the log is 
being erased. The blue (yellow) LED turns on when a packet is received and turns 
off when a packet has been logged successfully. The blue (yellow) LED remains on 
when packets are being received but are not logged (because the log is being 
erased). The green LED flickers rapidly after a power cycle when logged packets 
are transmitted. </P>
<OL>
  <LI>The first step when using the log is to decide what kind of data you want 
  to store in the log. In this case, we will declare a struct of the type: <PRE>  typedef nx_struct logentry_t {
    nx_uint8_t len;
    message_t msg;
  } logentry_t;
</PRE>
  <LI>Unlike Config storage, Log storage does not require the volume to be 
  explicitly mounted by the application. Instead, a simple read suffices in 
  which a buffer and the number of bytes to read are passed to 
  <CODE>LogRead.read</CODE>: <PRE>  event void AMControl.startDone(error_t err) {
    if (err == SUCCESS) {
      if (call LogRead.read(&amp;m_entry, sizeof(logentry_t))&nbsp;!= SUCCESS) {
        // Handle error
      }
    }
    else {
      call AMControl.start();
    }
  }
</PRE>
  <LI>If the call to <CODE>LogRead.read</CODE> returns SUCCESS, then a 
  <CODE>LogRead.readDone</CODE> event will be signaled shortly thereafter. When 
  that happens, we check if the data that was returned is the same length as 
  what we expected. If it is, we use the data but if not, we assume that either 
  the log is empty or that we have lost synchronization, so the log is erased: <PRE>  event void LogRead.readDone(void* buf, storage_len_t len, error_t err) {
    if ( (len == sizeof(logentry_t)) &amp;&amp; (buf == &amp;m_entry) ) {
      call Send.send(&amp;m_entry.msg, m_entry.len);
      call Leds.led1On();
    }
    else {
      if (call LogWrite.erase()&nbsp;!= SUCCESS) {
        // Handle error.
      }
      call Leds.led0On();
    }
  } 
</PRE>
  <LI>The <CODE>PacketParrot</CODE> application stores packets received over the 
  radio to flash by first saving the <CODE>message_t</CODE> and its length to a 
  <CODE>log_entry_t</CODE> struct and then calling <CODE>LogWrite.append</CODE>: 
<PRE>  event message_t* Receive.receive(message_t* msg, void* payload, uint8_t len){
    call Leds.led2On();
    if (!m_busy) {
      m_busy = TRUE;
      m_entry.len = len;
      m_entry.msg = *msg;
      if (call LogWrite.append(&amp;m_entry, sizeof(logentry_t))&nbsp;!= SUCCESS) {
        m_busy = FALSE;
      }
    }
    return msg;
  }
</PRE>
  <LI>If the <CODE>LogWrite.write</CODE> returned SUCCESS, then a short time 
  later, a <CODE>LogWrite.appendDone</CODE> will be signaled. This event returns 
  the details of the write including the source buffer, length of data written, 
  whether any records were lost (if this is a circular buffer) and any error 
  code. If no errors occurred, then the data was written to flash with 
  atomicity, consistency, and durability guarantees (and will survive node 
  crashes and reboots): <PRE>  event void LogWrite.appendDone(void* buf, storage_len_t len,
                                 bool recordsLost, error_t err) {
    m_busy = FALSE;
    call Leds.led2Off();
  }
</PRE></LI></OL><A name=Storing_Large_Objects></A>
<H1><SPAN class=mw-headline>Storing Large Objects</SPAN></H1>
<P>Block storage is generally used for storing large objects that cannot easily 
fit in RAM. Block is a low-level system interface that requires care when using 
since it is essentially a write-once model of storage. Rewriting requires an 
erase which is time-consuming, occurs at large granularity (e.g. 256 B to 64 
KB), and can only happen a limited number of times (e.g. 10,000 to 100,000 times 
is typical). The TinyOS network reprogramming system uses Block storage to store 
program images. </P>
<P>See <A class="external text" 
title=http://www.tinyos.net/tinyos-2.x/apps/tests/storage/Block/ 
href="http://www.tinyos.net/tinyos-2.x/apps/tests/storage/Block/" 
rel=nofollow><CODE>tinyos-2.x/apps/tests/storage/Block/</CODE></A> for an 
example of code that uses the Block storage abstraction. </P><A 
name=Conclusions></A>
<H1><SPAN class=mw-headline>Conclusions</SPAN></H1>
<P>This lesson introduced the basic storage abstractions in Tiny 2.x. </P><A 
name=Related_Documentation></A>
<H1><SPAN class=mw-headline>Related Documentation</SPAN></H1>
<OL class=references>
  <LI id=_note-fn1><A title="" 
  href="http://docs.tinyos.net/index.php/Storage#_ref-fn1_0">↑</A> <A 
  class="external text" 
  title=http://www.tinyos.net/tinyos-2.x/doc/html/tep103.html 
  href="http://www.tinyos.net/tinyos-2.x/doc/html/tep103.html" rel=nofollow>TEP 
  103: Permanent Data Storage</A></LI></OL>
<P><A title="Getting Started with TinyOS" 
href="http://docs.tinyos.net/index.php/Getting_Started_with_TinyOS">Getting 
Started with TinyOS and nesC</A> <I>TinyOS Programming</I> </P>
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