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- <a name="Packet-Acknowledgment"></a>
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- <p>
- 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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- <a name="Packet-Acknowledgment-1"></a>
- <h3 class="section">E.11 Packet Acknowledgment</h3>
-
- <a name="index-acknowledgment_002c-for-GDB-remote"></a>
- <a name="index-packet-acknowledgment_002c-for-GDB-remote"></a>
- <p>By default, when either the host or the target machine receives a packet,
- the first response expected is an acknowledgment: either ‘<samp>+</samp>’ (to indicate
- the package was received correctly) or ‘<samp>-</samp>’ (to request retransmission).
- This mechanism allows the <small>GDB</small> remote protocol to operate over
- unreliable transport mechanisms, such as a serial line.
- </p>
- <p>In cases where the transport mechanism is itself reliable (such as a pipe or
- TCP connection), the ‘<samp>+</samp>’/‘<samp>-</samp>’ acknowledgments are redundant.
- It may be desirable to disable them in that case to reduce communication
- overhead, or for other reasons. This can be accomplished by means of the
- ‘<samp>QStartNoAckMode</samp>’ packet; see <a href="General-Query-Packets.html#QStartNoAckMode">QStartNoAckMode</a>.
- </p>
- <p>When in no-acknowledgment mode, neither the stub nor <small>GDB</small> shall send or
- expect ‘<samp>+</samp>’/‘<samp>-</samp>’ protocol acknowledgments. The packet
- and response format still includes the normal checksum, as described in
- <a href="Overview.html#Overview">Overview</a>, but the checksum may be ignored by the receiver.
- </p>
- <p>If the stub supports ‘<samp>QStartNoAckMode</samp>’ and prefers to operate in
- no-acknowledgment mode, it should report that to <small>GDB</small>
- by including ‘<samp>QStartNoAckMode+</samp>’ in its response to ‘<samp>qSupported</samp>’;
- see <a href="General-Query-Packets.html#qSupported">qSupported</a>.
- If <small>GDB</small> also supports ‘<samp>QStartNoAckMode</samp>’ and it has not been
- disabled via the <code>set remote noack-packet off</code> command
- (see <a href="Remote-Configuration.html#Remote-Configuration">Remote Configuration</a>),
- <small>GDB</small> may then send a ‘<samp>QStartNoAckMode</samp>’ packet to the stub.
- Only then may the stub actually turn off packet acknowledgments.
- <small>GDB</small> sends a final ‘<samp>+</samp>’ acknowledgment of the stub’s ‘<samp>OK</samp>’
- response, which can be safely ignored by the stub.
- </p>
- <p>Note that <code>set remote noack-packet</code> command only affects negotiation
- between <small>GDB</small> and the stub when subsequent connections are made;
- it does not affect the protocol acknowledgment state for any current
- connection.
- Since ‘<samp>+</samp>’/‘<samp>-</samp>’ acknowledgments are enabled by default when a
- new connection is established,
- there is also no protocol request to re-enable the acknowledgments
- for the current connection, once disabled.
- </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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