URL
https://opencores.org/ocsvn/openrisc/openrisc/trunk
Subversion Repositories openrisc
[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [devapi-synchronization.html] - Rev 174
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
>Synchronization</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="Device Driver Interface to the Kernel"
HREF="devapi-device-driver-interface-to-the-kernel.html"><LINK
REL="PREVIOUS"
TITLE="Device Driver Interface to the Kernel"
HREF="devapi-device-driver-interface-to-the-kernel.html"><LINK
REL="NEXT"
TITLE="SMP Support"
HREF="devapi-smp-support.html"></HEAD
><BODY
CLASS="SECTION"
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="devapi-device-driver-interface-to-the-kernel.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 18. Device Driver Interface to the Kernel</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="devapi-smp-support.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECTION"
><H1
CLASS="SECTION"
><A
NAME="DEVAPI-SYNCHRONIZATION">Synchronization</H1
><P
>There are three levels of synchronization supported:</P
><P
></P
><OL
TYPE="1"
><LI
><P
> Synchronization with ISRs. This normally means disabling
interrupts to prevent the ISR running during a critical
section. In an SMP environment, this will also require the use of
a spinlock to synchronize with ISRs, DSRs or threads running on
other CPUs. This is implemented by the
<TT
CLASS="FUNCTION"
>cyg_drv_isr_lock()</TT
> and
<TT
CLASS="FUNCTION"
>cyg_drv_isr_unlock()</TT
> functions. This
mechanism should be used sparingly and for short periods only.
For finer grained synchronization, individual spinlocks are also
supplied.
</P
></LI
><LI
><P
> Synchronization with DSRs. This will be implemented in the kernel
by taking the scheduler lock to prevent DSRs running during
critical sections. In non-kernel configurations it will be
implemented by non-kernel code. This is implemented by the
<TT
CLASS="FUNCTION"
>cyg_drv_dsr_lock()</TT
> and
<TT
CLASS="FUNCTION"
>cyg_drv_dsr_unlock()</TT
> functions. As with ISR
synchronization, this mechanism should be used sparingly. Only
DSRs and threads may use this synchronization mechanism, ISRs are
not allowed to do this.
</P
></LI
><LI
><P
> Synchronization with threads. This is implemented with mutexes
and condition variables. Only threads may lock the mutexes and
wait on the condition variables, although DSRs may signal
condition variables.
</P
></LI
></OL
><P
>Any data that is accessed from more than one level must be protected
against concurrent access. Data that is accessed by ISRs must be
protected with the ISR lock, or a spinlock at all times,
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>even in ISRs</I
></SPAN
>. Data that is shared between DSRs
and threads should be protected with the DSR lock. Data that is only
accessed by threads must be protected with mutexes.</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="devapi-device-driver-interface-to-the-kernel.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="devapi-smp-support.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Device Driver Interface to the Kernel</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="devapi-device-driver-interface-to-the-kernel.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>SMP Support</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>