URL
https://opencores.org/ocsvn/openrisc_2011-10-31/openrisc_2011-10-31/trunk
Subversion Repositories openrisc_2011-10-31
[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [c-library-startup.html] - Rev 482
Go to most recent revision | Compare with Previous | Blame | View Log
<!-- Copyright (C) 2003 Red Hat, Inc. -->
<!-- This material may be distributed only subject to the terms -->
<!-- and conditions set forth in the Open Publication License, v1.0 -->
<!-- or later (the latest version is presently available at -->
<!-- http://www.opencontent.org/openpub/). -->
<!-- Distribution of the work or derivative of the work in any -->
<!-- standard (paper) book form is prohibited unless prior -->
<!-- permission is obtained from the copyright holder. -->
<HTML
><HEAD
><TITLE
>C library startup</TITLE
><meta name="MSSmartTagsPreventParsing" content="TRUE">
<META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
TITLE="eCos Reference Manual"
HREF="ecos-ref.html"><LINK
REL="UP"
TITLE="C and math library overview"
HREF="c-and-math-library-overview.html"><LINK
REL="PREVIOUS"
TITLE="Thread safety"
HREF="libc-thread-safety.html"><LINK
REL="NEXT"
TITLE="I/O Package (Device Drivers)"
HREF="io.html"></HEAD
><BODY
CLASS="SECT1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>eCos Reference Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="libc-thread-safety.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 13. C and math library overview</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="io.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="C-LIBRARY-STARTUP">C library startup</H1
><P
>The C library includes a function declared as:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>void <TT
CLASS="FUNCTION"
>cyg_iso_c_start</TT
>( void )</PRE
></TD
></TR
></TABLE
><P
>This function is used to start an environment in which an
ISO C style program can run in the most compatible way.</P
><P
>What this function does is to create a thread which will invoke <TT
CLASS="FUNCTION"
>main()</TT
> — normally
considered a program's entry point. In particular, it can
supply arguments to <TT
CLASS="FUNCTION"
>main()</TT
> using the CYGDAT_LIBC_ARGUMENTS
configuration option, and when returning from <TT
CLASS="FUNCTION"
>main()</TT
>,
or calling <TT
CLASS="FUNCTION"
>exit()</TT
>, pending stdio file output
is flushed and any functions registered with <TT
CLASS="FUNCTION"
>atexit()</TT
> are
invoked. This is all compliant with the ISO C standard in this respect. </P
><P
>This thread starts execution when the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
> scheduler
is started. If the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
> kernel package is not
available (and hence there is no scheduler), then <TT
CLASS="FUNCTION"
>cyg_iso_c_start()</TT
> will
invoke the <TT
CLASS="FUNCTION"
>main()</TT
> function directly, i.e.
it will not return until the <TT
CLASS="FUNCTION"
>main()</TT
> function
returns. </P
><P
>The <TT
CLASS="FUNCTION"
>main()</TT
> function should be defined
as the following, and if defined in a C++ file,
should have “C” linkage: </P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>extern int <TT
CLASS="FUNCTION"
>main</TT
>(
int <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>argc,</I
></SPAN
>
char *<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>argv[] </I
></SPAN
>)</PRE
></TD
></TR
></TABLE
><P
>The thread that is started by <TT
CLASS="FUNCTION"
>cyg_iso_c_start()</TT
> can
be manipulated directly, if you wish. For example you can suspend
it. The kernel C API needs a handle to do this, which is available
by including the following in your source code.</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>extern cyg_handle_t cyg_libc_main_thread;</PRE
></TD
></TR
></TABLE
><P
>Then for example, you can suspend the thread with the line:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cyg_thread_suspend( cyg_libc_main_thread );</PRE
></TD
></TR
></TABLE
><P
>If you call <TT
CLASS="FUNCTION"
>cyg_iso_c_start()</TT
> and
do not provide your own <TT
CLASS="FUNCTION"
>main()</TT
> function,
the system will provide a <TT
CLASS="FUNCTION"
>main()</TT
> for you
which will simply return immediately.</P
><P
>In the default configuration, <TT
CLASS="FUNCTION"
>cyg_iso_c_start()</TT
> is
invoked automatically by the <TT
CLASS="FUNCTION"
>cyg_package_start()</TT
> function
in the infrastructure configuration. This means that in the simplest
case, your program can indeed consist of simply:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>int main( int argc, char *argv[] )
{
printf("Hello eCos\n");
}</PRE
></TD
></TR
></TABLE
><P
>If you override <TT
CLASS="FUNCTION"
>cyg_package_start()</TT
> or <TT
CLASS="FUNCTION"
>cyg_start()</TT
>,
or disable the infrastructure configuration option CYGSEM_START_ISO_C_COMPATIBILITY
then you must ensure that you call <TT
CLASS="FUNCTION"
>cyg_iso_c_start()</TT
> yourself
if you want to be able to have your program start at the entry point
of <TT
CLASS="FUNCTION"
>main()</TT
> automatically.</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="libc-thread-safety.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="ecos-ref.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="io.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Thread safety</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c-and-math-library-overview.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>I/O Package (Device Drivers)</TD
></TR
></TABLE
></DIV
></BODY
></HTML
> Go to most recent revision | Compare with Previous | Blame | View Log