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<H1 class=firstHeading>The TinyOS printf Library</H1>
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<P>This lesson demonstrates how to use the <CODE>printf</CODE> library located
in <CODE>tos/lib/printf</CODE> to debug TinyOS applications by printing messages
over the serial port. </P>
<TABLE class=toc id=toc summary=Contents>
<TBODY>
<TR>
<TD>
<DIV id=toctitle>
<H2>Contents</H2></DIV>
<UL>
<LI class=toclevel-1><A
href="http://docs.tinyos.net/index.php/The_TinyOS_printf_Library#Overview"><SPAN
class=tocnumber>1</SPAN> <SPAN class=toctext>Overview</SPAN></A>
<LI class=toclevel-1><A
href="http://docs.tinyos.net/index.php/The_TinyOS_printf_Library#The_TinyOS_printf_Library"><SPAN
class=tocnumber>2</SPAN> <SPAN class=toctext>The TinyOS printf
Library</SPAN></A>
<LI class=toclevel-1><A
href="http://docs.tinyos.net/index.php/The_TinyOS_printf_Library#Using_the_TinyOS_printf_Library"><SPAN
class=tocnumber>3</SPAN> <SPAN class=toctext>Using the TinyOS printf
Library</SPAN></A>
<LI class=toclevel-1><A
href="http://docs.tinyos.net/index.php/The_TinyOS_printf_Library#Conclusion"><SPAN
class=tocnumber>4</SPAN> <SPAN class=toctext>Conclusion</SPAN></A>
</LI></UL></TD></TR></TBODY></TABLE>
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<A name=Overview></A>
<H1><SPAN class=mw-headline>Overview</SPAN></H1>
<P>Anyone familiar with TinyOS knows that debugging applications has
traditionally been a very arduous, if not stressful process. While simulators
like TOSSIM can be used to help verify the logical correctness of a program,
unforseen problems inevitably arise once that program is deployed on real
hardware. Debugging such a program typically involves flashing the three
available LEDs in some intricate sequence or resorting to line by line analysis
of a running program through the use of a JTAG. </P>
<P>It is common practice when developing desktop applications to print output to
the terminal screen for debugging purposes. While tools such as <CODE>gdb</CODE>
provide means of stepping though a program line by line, often times developers
simply want to quickly print something to the screen to verify that the value of
a variable has been set correctly, or determine that some sequence of events is
being run in the proper order. It would be absurd to suggest that they only be
allowed three bits of information in order to do so. </P>
<P>The TinyOS <CODE>printf</CODE> library provides this terminal printing
functionality to TinyOS applications through motes connected to a pc via their
serial interface. Messages are printed by calling <CODE>printf</CODE> commands
using a familiar syntax borrowed from the C programming language. In order to
use this functionality, developers simply need to include a single component in
their top level configuration file (<CODE>PrintfC</CODE>), and include a
<CODE>"printf.h"</CODE> header file in any components that actually call
<CODE>printf()</CODE>. </P>
<P>Currently, the <CODE>printf</CODE> library is only supported on msp430 and
atmega128x based platforms (e.g. mica2, micaZ, telos, eyesIFX). In the future we
hope to add support for other platforms as well. </P><A
name=The_TinyOS_printf_Library></A>
<H1><SPAN class=mw-headline>The TinyOS <CODE>printf</CODE> Library</SPAN></H1>
<P>This section provides a basic overview of the TinyOS <CODE>printf</CODE>
library, including the components that make it up and the interfaces they
provide. In the following section we walk you through the process of actually
using these components to print messages from a mote to your pc. If you dont
care how <CODE>printf</CODE> works and only want to know how to use it, feel
free to skip ahead to the next section. </P>
<HR>
<P>The entire <CODE>printf</CODE> library consists of only 4 files located in
the <CODE>tos/lib/printf</CODE> directory: one module, one configuration, one
interface file, and one header file. </P>
<UL>
<LI><B>PrintfC.nc</B> -- Configuration file providing printf functionality to
TinyOS applications
<LI><B>PrintfP.nc</B> -- Module implementing the printf functionality
<LI><B>PrintfFlush.nc</B> -- Interface for flushing printf messages over the
serial port to a pc
<LI><B>printf.h</B> -- Header file specifying the printf message format and
size of the flush buffer </LI></UL>
<P>The <CODE>PrintfC</CODE> configuration is the only component an application
needs to wire in order to use the functionality provided by the TinyOS
<CODE>printf</CODE> library. Below is the component graph of the
<CODE>PrintfC</CODE> configuration: </P>
<CENTER><A class=image title=Image:printf_components.png
href="http://docs.tinyos.net/index.php/Image:Printf_components.png"><IMG
height=293 alt=Image:printf_components.png
src="The TinyOS printf Library - TinyOS Documentation Wiki.files/Printf_components.png"
width=363 border=0></A>
<P><B>Figure 1: The component graph of the PrintfC configuration.</B>
</P></CENTER>
<P>Conceptually, the operation of the TinyOS <CODE>printf</CODE> library is very
simple. Developers supply strings to <CODE>printf()</CODE> commands in a
distributed fashion throughout any of the components that make up a complete
TinyOS application. These strings are buffered in a central location inside the
<CODE>PrintfP</CODE> component and flushed out to a PC in the form of TinyOS
SerialMessages upon calling the <CODE>flush()</CODE> command of the
<CODE>PrintfFlush</CODE> interface. </P>
<P>By encapsulating the strings produced by calls to <CODE>printf()</CODE>
inside standard TinyOS SerialMessages, applications that use the serial stack
for other purposes can share the use of the serial port. Alternate
implementations were considered in which <CODE>printf</CODE> would have had
exclusive access to the serial port, and explicit flushing would not have been
necessary. In the end, we felt it was better to give developers the freedom to
decide exactly when messages should be printed, as well as allow them to send
multiple types of SerialMessages in a single application. </P>
<P>Currently, only a single buffer is used to store the strings supplied to
calls to <CODE>printf</CODE> before flushing them. This means that while the
buffer is being flushed, any calls to <CODE>printf</CODE> will fail. In the
future, we plan to implement a double buffered approach so that strings can
continue to be buffered at the same time they are being printed. </P>
<P>There are also plans to provide a means of flushing messages out to a PC
without requiring developers to make an explicit <CODE>flush()</CODE> call. This
would allow developers to simply wire in the <CODE>PrintfC</CODE> component
without having to make any calls to any interfaces it provides. In fact, the
<CODE>PrintfC</CODE> component would not need to provide any interfaces at all.
It would start itself up and then run in a loop, periodically flushing the
contents of the <CODE>printf</CODE> buffer. Such functionality is useful in
applications that do not really care when messages are printed or how long a
delay the process of printing introduces to other sections of code. Explicit
flushing would still be recommended in applications where the sections of code
under examinatation are very timing sensitive (e.g. inside the CC2420 radio
stack). </P><A name=Using_the_TinyOS_printf_Library></A>
<H1><SPAN class=mw-headline>Using the TinyOS <CODE>printf</CODE>
Library</SPAN></H1>
<P>To help guide the process of using the <CODE>printf</CODE> library, a
<CODE>TestPrintf</CODE> application has been created. At present, this
application is not included in the official TinyOS distribution (<= 2.0.2).
If you are using TinyOS from a cvs checkout, you will find it located under
<CODE>apps/tutorials/Printf</CODE>. Otherwise, you can obtain it from cvs by
running the following set of commands from a terminal window: </P><PRE>cd $TOSROOT/apps/tutorials
cvs -d:pserver:anonymous@tinyos.cvs.sourceforge.net:/cvsroot/tinyos login
cvs -z3 -d:pserver:anonymous@tinyos.cvs.sourceforge.net:/cvsroot/tinyos co -P -d Printf tinyos-2.x/apps/tutorials/Printf
</PRE>
<P>Just hit enter when prompted for a CVS password. You do not need to enter
one. </P>
<P>If you are not using cvs, you will also have to apply the patch found <A
class="external text"
title=http://sing.stanford.edu/klueska/tinyos-2.0-printf.patch
href="http://sing.stanford.edu/klueska/tinyos-2.0-printf.patch"
rel=nofollow>here</A> in order to allow the <CODE>printf</CODE> library to
compile correctly for atmega128x based platforms (i.e. mica2, micaz): </P><PRE>cp tinyos-2.0-printf.patch $TOSROOT/..
cd $TOSROOT/..
patch -p0 < tinyos-2.0-printf.patch
</PRE>
<P>Note that you may have to use 'sudo' when applying the patch if you run into
permission problems. </P>
<HR>
<P>The <CODE>TestPrintf</CODE> application demonstrates everything necessary to
use the <CODE>printf</CODE> library. Go ahead and open the
<CODE>TestPrintfAppC</CODE> configuration to see how the various interfaces
provided by the <CODE>PrintfC</CODE> component have been wired in. You will want
to do something similar in your own applications. </P><PRE>configuration TestPrintfAppC{
}
implementation {
components MainC, TestPrintfC, LedsC;
components PrintfC;
TestPrintfC.Boot -> MainC;
TestPrintfC.Leds -> LedsC;
TestPrintfC.PrintfControl -> PrintfC;
TestPrintfC.PrintfFlush -> PrintfC;
}
</PRE>
<P>First, the <CODE>PrintfControl</CODE> interface has been wired in to enable
turning on and off the service providing <CODE>printf</CODE> functionality.
Turning on the <CODE>Printf</CODE> service implicity turns on the serial port
for sending messages. Second, the <CODE>PrintfFlush</CODE> interface has been
wired in to allow the application to control when <CODE>printf</CODE> messages
should be flushed out over the serial line. In this application, all
<CODE>printf()</CODE> commands are called directly within the
<CODE>TestPrintfC</CODE> component. In general, <CODE>printf()</CODE> commands
can be called from any component as long as they have included the
<CODE>"printf.h"</CODE> header file. </P>
<HR>
<P>Before examining the <CODE>TestPrintfC</CODE> component, first install the
application on a mote and see what kind of output it produces. Note that the
instructions here are only valid for installation on a telosb mote on a linux
based TinyOS distribution. For installation on other systems or for other mote
platforms, please refer to <A title="Getting Started with TinyOS"
href="http://docs.tinyos.net/index.php/Getting_Started_with_TinyOS">lesson 1</A>
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