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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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><H1
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><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
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>

Line No.	Rev	Author	Line
1	28	unneback	`<!-- Copyright (C) 2003 Red Hat, Inc. -->`
2			`<!-- This material may be distributed only subject to the terms -->`
3			`<!-- and conditions set forth in the Open Publication License, v1.0 -->`
4			`<!-- or later (the latest version is presently available at -->`
5			`<!-- http://www.opencontent.org/openpub/). -->`
6			`<!-- Distribution of the work or derivative of the work in any -->`
7			`<!-- standard (paper) book form is prohibited unless prior -->`
8			`<!-- permission is obtained from the copyright holder. -->`
9			`<HTML`
10			`><HEAD`
11			`><TITLE`
12			`>Synchronization</TITLE`
13			`><meta name="MSSmartTagsPreventParsing" content="TRUE">`
14			`<META`
15			`NAME="GENERATOR"`
16			`CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+`
17			`"><LINK`
18			`REL="HOME"`
19			`TITLE="eCos Reference Manual"`
20			`HREF="ecos-ref.html"><LINK`
21			`REL="UP"`
22			`TITLE="Device Driver Interface to the Kernel"`
23			`HREF="devapi-device-driver-interface-to-the-kernel.html"><LINK`
24			`REL="PREVIOUS"`
25			`TITLE="Device Driver Interface to the Kernel"`
26			`HREF="devapi-device-driver-interface-to-the-kernel.html"><LINK`
27			`REL="NEXT"`
28			`TITLE="SMP Support"`
29			`HREF="devapi-smp-support.html"></HEAD`
30			`><BODY`
31			`CLASS="SECTION"`
32			`BGCOLOR="#FFFFFF"`
33			`TEXT="#000000"`
34			`LINK="#0000FF"`
35			`VLINK="#840084"`
36			`ALINK="#0000FF"`
37			`><DIV`
38			`CLASS="NAVHEADER"`
39			`><TABLE`
40			`SUMMARY="Header navigation table"`
41			`WIDTH="100%"`
42			`BORDER="0"`
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44			`CELLSPACING="0"`
45			`><TR`
46			`><TH`
47			`COLSPAN="3"`
48			`ALIGN="center"`
49			`>eCos Reference Manual</TH`
50			`></TR`
51			`><TR`
52			`><TD`
53			`WIDTH="10%"`
54			`ALIGN="left"`
55			`VALIGN="bottom"`
56			`><A`
57			`HREF="devapi-device-driver-interface-to-the-kernel.html"`
58			`ACCESSKEY="P"`
59			`>Prev</A`
60			`></TD`
61			`><TD`
62			`WIDTH="80%"`
63			`ALIGN="center"`
64			`VALIGN="bottom"`
65			`>Chapter 18. Device Driver Interface to the Kernel</TD`
66			`><TD`
67			`WIDTH="10%"`
68			`ALIGN="right"`
69			`VALIGN="bottom"`
70			`><A`
71			`HREF="devapi-smp-support.html"`
72			`ACCESSKEY="N"`
73			`>Next</A`
74			`></TD`
75			`></TR`
76			`></TABLE`
77			`><HR`
78			`ALIGN="LEFT"`
79			`WIDTH="100%"></DIV`
80			`><DIV`
81			`CLASS="SECTION"`
82			`><H1`
83			`CLASS="SECTION"`
84			`><A`
85			`NAME="DEVAPI-SYNCHRONIZATION">Synchronization</H1`
86			`><P`
87			`>There are three levels of synchronization supported:</P`
88			`><P`
89			`></P`
90			`><OL`
91			`TYPE="1"`
92			`><LI`
93			`><P`
94			`> Synchronization with ISRs. This normally means disabling`
95			`interrupts to prevent the ISR running during a critical`
96			`section. In an SMP environment, this will also require the use of`
97			`a spinlock to synchronize with ISRs, DSRs or threads running on`
98			`other CPUs. This is implemented by the`
99			`<TT`
100			`CLASS="FUNCTION"`
101			`>cyg_drv_isr_lock()</TT`
102			`> and`
103			`<TT`
104			`CLASS="FUNCTION"`
105			`>cyg_drv_isr_unlock()</TT`
106			`> functions. This`
107			`mechanism should be used sparingly and for short periods only.`
108			`For finer grained synchronization, individual spinlocks are also`
109			`supplied.`
110			`</P`
111			`></LI`
112			`><LI`
113			`><P`
114			`> Synchronization with DSRs. This will be implemented in the kernel`
115			`by taking the scheduler lock to prevent DSRs running during`
116			`critical sections. In non-kernel configurations it will be`
117			`implemented by non-kernel code. This is implemented by the`
118			`<TT`
119			`CLASS="FUNCTION"`
120			`>cyg_drv_dsr_lock()</TT`
121			`> and`
122			`<TT`
123			`CLASS="FUNCTION"`
124			`>cyg_drv_dsr_unlock()</TT`
125			`> functions. As with ISR`
126			`synchronization, this mechanism should be used sparingly. Only`
127			`DSRs and threads may use this synchronization mechanism, ISRs are`
128			`not allowed to do this.`
129			`</P`
130			`></LI`
131			`><LI`
132			`><P`
133			`> Synchronization with threads. This is implemented with mutexes`
134			`and condition variables. Only threads may lock the mutexes and`
135			`wait on the condition variables, although DSRs may signal`
136			`condition variables.`
137			`</P`
138			`></LI`
139			`></OL`
140			`><P`
141			`>Any data that is accessed from more than one level must be protected`
142			`against concurrent access. Data that is accessed by ISRs must be`
143			`protected with the ISR lock, or a spinlock at all times,`
144			`<SPAN`
145			`CLASS="emphasis"`
146			`><I`
147			`CLASS="EMPHASIS"`
148			`>even in ISRs</I`
149			`></SPAN`
150			`>. Data that is shared between DSRs`
151			`and threads should be protected with the DSR lock. Data that is only`
152			`accessed by threads must be protected with mutexes.</P`
153			`></DIV`
154			`><DIV`
155			`CLASS="NAVFOOTER"`
156			`><HR`
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158			`WIDTH="100%"><TABLE`
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193			`><TR`
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196			`ALIGN="left"`
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198			`>Device Driver Interface to the Kernel</TD`
199			`><TD`
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212			`>SMP Support</TD`
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217			`></HTML`
218			`>`

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