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<!-- 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 >
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