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122 lines
6.5 KiB
HTML
122 lines
6.5 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Packet Acknowledgment (Debugging with GDB)</title>
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<meta name="description" content="Packet Acknowledgment (Debugging with GDB)">
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<meta name="keywords" content="Packet Acknowledgment (Debugging with GDB)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Remote-Protocol.html#Remote-Protocol" rel="up" title="Remote Protocol">
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<link href="Examples.html#Examples" rel="next" title="Examples">
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<link href="Remote-Non_002dStop.html#Remote-Non_002dStop" rel="prev" title="Remote Non-Stop">
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</style>
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</head>
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<body lang="en">
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<a name="Packet-Acknowledgment"></a>
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<div class="header">
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<p>
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Next: <a href="Examples.html#Examples" accesskey="n" rel="next">Examples</a>, Previous: <a href="Remote-Non_002dStop.html#Remote-Non_002dStop" accesskey="p" rel="prev">Remote Non-Stop</a>, Up: <a href="Remote-Protocol.html#Remote-Protocol" accesskey="u" rel="up">Remote Protocol</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Packet-Acknowledgment-1"></a>
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<h3 class="section">E.11 Packet Acknowledgment</h3>
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<a name="index-acknowledgment_002c-for-GDB-remote"></a>
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<a name="index-packet-acknowledgment_002c-for-GDB-remote"></a>
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<p>By default, when either the host or the target machine receives a packet,
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the first response expected is an acknowledgment: either ‘<samp>+</samp>’ (to indicate
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the package was received correctly) or ‘<samp>-</samp>’ (to request retransmission).
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This mechanism allows the <small>GDB</small> remote protocol to operate over
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unreliable transport mechanisms, such as a serial line.
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</p>
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<p>In cases where the transport mechanism is itself reliable (such as a pipe or
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TCP connection), the ‘<samp>+</samp>’/‘<samp>-</samp>’ acknowledgments are redundant.
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It may be desirable to disable them in that case to reduce communication
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overhead, or for other reasons. This can be accomplished by means of the
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‘<samp>QStartNoAckMode</samp>’ packet; see <a href="General-Query-Packets.html#QStartNoAckMode">QStartNoAckMode</a>.
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</p>
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<p>When in no-acknowledgment mode, neither the stub nor <small>GDB</small> shall send or
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expect ‘<samp>+</samp>’/‘<samp>-</samp>’ protocol acknowledgments. The packet
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and response format still includes the normal checksum, as described in
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<a href="Overview.html#Overview">Overview</a>, but the checksum may be ignored by the receiver.
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</p>
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<p>If the stub supports ‘<samp>QStartNoAckMode</samp>’ and prefers to operate in
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no-acknowledgment mode, it should report that to <small>GDB</small>
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by including ‘<samp>QStartNoAckMode+</samp>’ in its response to ‘<samp>qSupported</samp>’;
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see <a href="General-Query-Packets.html#qSupported">qSupported</a>.
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If <small>GDB</small> also supports ‘<samp>QStartNoAckMode</samp>’ and it has not been
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disabled via the <code>set remote noack-packet off</code> command
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(see <a href="Remote-Configuration.html#Remote-Configuration">Remote Configuration</a>),
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<small>GDB</small> may then send a ‘<samp>QStartNoAckMode</samp>’ packet to the stub.
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Only then may the stub actually turn off packet acknowledgments.
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<small>GDB</small> sends a final ‘<samp>+</samp>’ acknowledgment of the stub’s ‘<samp>OK</samp>’
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response, which can be safely ignored by the stub.
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</p>
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<p>Note that <code>set remote noack-packet</code> command only affects negotiation
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between <small>GDB</small> and the stub when subsequent connections are made;
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it does not affect the protocol acknowledgment state for any current
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connection.
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Since ‘<samp>+</samp>’/‘<samp>-</samp>’ acknowledgments are enabled by default when a
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new connection is established,
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there is also no protocol request to re-enable the acknowledgments
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for the current connection, once disabled.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Examples.html#Examples" accesskey="n" rel="next">Examples</a>, Previous: <a href="Remote-Non_002dStop.html#Remote-Non_002dStop" accesskey="p" rel="prev">Remote Non-Stop</a>, Up: <a href="Remote-Protocol.html#Remote-Protocol" accesskey="u" rel="up">Remote Protocol</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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