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199 lines
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HTML
199 lines
10 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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<html>
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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>Notification Packets (Debugging with GDB)</title>
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<meta name="description" content="Notification Packets (Debugging with GDB)">
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<meta name="keywords" content="Notification Packets (Debugging with GDB)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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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="Remote-Non_002dStop.html#Remote-Non_002dStop" rel="next" title="Remote Non-Stop">
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<link href="Interrupts.html#Interrupts" rel="prev" title="Interrupts">
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</style>
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</head>
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<body lang="en">
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<a name="Notification-Packets"></a>
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<div class="header">
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<p>
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Next: <a href="Remote-Non_002dStop.html#Remote-Non_002dStop" accesskey="n" rel="next">Remote Non-Stop</a>, Previous: <a href="Interrupts.html#Interrupts" accesskey="p" rel="prev">Interrupts</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="Notification-Packets-1"></a>
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<h3 class="section">E.9 Notification Packets</h3>
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<a name="index-notification-packets"></a>
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<a name="index-packets_002c-notification"></a>
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<p>The <small>GDB</small> remote serial protocol includes <em>notifications</em>,
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packets that require no acknowledgment. Both the GDB and the stub
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may send notifications (although the only notifications defined at
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present are sent by the stub). Notifications carry information
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without incurring the round-trip latency of an acknowledgment, and so
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are useful for low-impact communications where occasional packet loss
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is not a problem.
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</p>
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<p>A notification packet has the form ‘<samp>% <var>data</var> #
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<var>checksum</var></samp>’, where <var>data</var> is the content of the notification,
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and <var>checksum</var> is a checksum of <var>data</var>, computed and formatted
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as for ordinary <small>GDB</small> packets. A notification’s <var>data</var>
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never contains ‘<samp>$</samp>’, ‘<samp>%</samp>’ or ‘<samp>#</samp>’ characters. Upon
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receiving a notification, the recipient sends no ‘<samp>+</samp>’ or ‘<samp>-</samp>’
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to acknowledge the notification’s receipt or to report its corruption.
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</p>
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<p>Every notification’s <var>data</var> begins with a name, which contains no
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colon characters, followed by a colon character.
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</p>
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<p>Recipients should silently ignore corrupted notifications and
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notifications they do not understand. Recipients should restart
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timeout periods on receipt of a well-formed notification, whether or
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not they understand it.
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</p>
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<p>Senders should only send the notifications described here when this
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protocol description specifies that they are permitted. In the
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future, we may extend the protocol to permit existing notifications in
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new contexts; this rule helps older senders avoid confusing newer
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recipients.
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</p>
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<p>(Older versions of <small>GDB</small> ignore bytes received until they see
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the ‘<samp>$</samp>’ byte that begins an ordinary packet, so new stubs may
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transmit notifications without fear of confusing older clients. There
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are no notifications defined for <small>GDB</small> to send at the moment, but we
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assume that most older stubs would ignore them, as well.)
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</p>
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<p>Each notification is comprised of three parts:
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</p><dl compact="compact">
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<dt>‘<samp><var>name</var>:<var>event</var></samp>’</dt>
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<dd><p>The notification packet is sent by the side that initiates the
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exchange (currently, only the stub does that), with <var>event</var>
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carrying the specific information about the notification, and
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<var>name</var> specifying the name of the notification.
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</p></dd>
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<dt>‘<samp><var>ack</var></samp>’</dt>
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<dd><p>The acknowledge sent by the other side, usually <small>GDB</small>, to
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acknowledge the exchange and request the event.
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</p></dd>
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</dl>
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<p>The purpose of an asynchronous notification mechanism is to report to
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<small>GDB</small> that something interesting happened in the remote stub.
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</p>
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<p>The remote stub may send notification <var>name</var>:<var>event</var>
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at any time, but <small>GDB</small> acknowledges the notification when
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appropriate. The notification event is pending before <small>GDB</small>
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acknowledges. Only one notification at a time may be pending; if
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additional events occur before <small>GDB</small> has acknowledged the
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previous notification, they must be queued by the stub for later
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synchronous transmission in response to <var>ack</var> packets from
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<small>GDB</small>. Because the notification mechanism is unreliable,
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the stub is permitted to resend a notification if it believes
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<small>GDB</small> may not have received it.
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</p>
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<p>Specifically, notifications may appear when <small>GDB</small> is not
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otherwise reading input from the stub, or when <small>GDB</small> is
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expecting to read a normal synchronous response or a
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‘<samp>+</samp>’/‘<samp>-</samp>’ acknowledgment to a packet it has sent.
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Notification packets are distinct from any other communication from
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the stub so there is no ambiguity.
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</p>
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<p>After receiving a notification, <small>GDB</small> shall acknowledge it by
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sending a <var>ack</var> packet as a regular, synchronous request to the
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stub. Such acknowledgment is not required to happen immediately, as
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<small>GDB</small> is permitted to send other, unrelated packets to the
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stub first, which the stub should process normally.
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</p>
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<p>Upon receiving a <var>ack</var> packet, if the stub has other queued
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events to report to <small>GDB</small>, it shall respond by sending a
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normal <var>event</var>. <small>GDB</small> shall then send another <var>ack</var>
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packet to solicit further responses; again, it is permitted to send
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other, unrelated packets as well which the stub should process
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normally.
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</p>
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<p>If the stub receives a <var>ack</var> packet and there are no additional
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<var>event</var> to report, the stub shall return an ‘<samp>OK</samp>’ response.
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At this point, <small>GDB</small> has finished processing a notification
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and the stub has completed sending any queued events. <small>GDB</small>
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won’t accept any new notifications until the final ‘<samp>OK</samp>’ is
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received . If further notification events occur, the stub shall send
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a new notification, <small>GDB</small> shall accept the notification, and
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the process shall be repeated.
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</p>
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<p>The process of asynchronous notification can be illustrated by the
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following example:
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</p><div class="smallexample">
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<pre class="smallexample"><- <code>%Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;</code>
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<code>...</code>
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-> <code>vStopped</code>
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<- <code>T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;</code>
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-> <code>vStopped</code>
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<- <code>T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;</code>
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-> <code>vStopped</code>
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<- <code>OK</code>
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</pre></div>
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<p>The following notifications are defined:
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</p><table>
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<tr><td width="12%">Notification</td><td width="12%">Ack</td><td width="38%">Event</td><td width="38%">Description</td></tr>
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<tr><td width="12%">Stop</td><td width="12%">vStopped</td><td width="38%"><var>reply</var>. The <var>reply</var> has the form of a stop reply, as
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described in <a href="Stop-Reply-Packets.html#Stop-Reply-Packets">Stop Reply Packets</a>. Refer to <a href="Remote-Non_002dStop.html#Remote-Non_002dStop">Remote Non-Stop</a>,
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for information on how these notifications are acknowledged by
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<small>GDB</small>.</td><td width="38%">Report an asynchronous stop event in non-stop mode.</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Remote-Non_002dStop.html#Remote-Non_002dStop" accesskey="n" rel="next">Remote Non-Stop</a>, Previous: <a href="Interrupts.html#Interrupts" accesskey="p" rel="prev">Interrupts</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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