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| <a name="Notification-Packets"></a> |
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| <h3 class="section">E.9 Notification Packets</h3> |
| |
| <p><a name="index-notification-packets-3590"></a><a name="index-packets_002c-notification-3591"></a> |
| The <span class="sc">gdb</span> remote serial protocol includes <dfn>notifications</dfn>, |
| packets that require no acknowledgment. Both the GDB and the stub |
| may send notifications (although the only notifications defined at |
| present are sent by the stub). Notifications carry information |
| without incurring the round-trip latency of an acknowledgment, and so |
| are useful for low-impact communications where occasional packet loss |
| is not a problem. |
| |
| <p>A notification packet has the form ‘<samp><span class="samp">% </span><var>data</var><span class="samp"> # |
| </span><var>checksum</var></samp>’, where <var>data</var> is the content of the notification, |
| and <var>checksum</var> is a checksum of <var>data</var>, computed and formatted |
| as for ordinary <span class="sc">gdb</span> packets. A notification's <var>data</var> |
| never contains ‘<samp><span class="samp">$</span></samp>’, ‘<samp><span class="samp">%</span></samp>’ or ‘<samp><span class="samp">#</span></samp>’ characters. Upon |
| receiving a notification, the recipient sends no ‘<samp><span class="samp">+</span></samp>’ or ‘<samp><span class="samp">-</span></samp>’ |
| to acknowledge the notification's receipt or to report its corruption. |
| |
| <p>Every notification's <var>data</var> begins with a name, which contains no |
| colon characters, followed by a colon character. |
| |
| <p>Recipients should silently ignore corrupted notifications and |
| notifications they do not understand. Recipients should restart |
| timeout periods on receipt of a well-formed notification, whether or |
| not they understand it. |
| |
| <p>Senders should only send the notifications described here when this |
| protocol description specifies that they are permitted. In the |
| future, we may extend the protocol to permit existing notifications in |
| new contexts; this rule helps older senders avoid confusing newer |
| recipients. |
| |
| <p>(Older versions of <span class="sc">gdb</span> ignore bytes received until they see |
| the ‘<samp><span class="samp">$</span></samp>’ byte that begins an ordinary packet, so new stubs may |
| transmit notifications without fear of confusing older clients. There |
| are no notifications defined for <span class="sc">gdb</span> to send at the moment, but we |
| assume that most older stubs would ignore them, as well.) |
| |
| <p>Each notification is comprised of three parts: |
| <dl> |
| <dt>‘<samp><var>name</var><span class="samp">:</span><var>event</var></samp>’<dd>The notification packet is sent by the side that initiates the |
| exchange (currently, only the stub does that), with <var>event</var> |
| carrying the specific information about the notification, and |
| <var>name</var> specifying the name of the notification. |
| <br><dt>‘<samp><var>ack</var></samp>’<dd>The acknowledge sent by the other side, usually <span class="sc">gdb</span>, to |
| acknowledge the exchange and request the event. |
| </dl> |
| |
| <p>The purpose of an asynchronous notification mechanism is to report to |
| <span class="sc">gdb</span> that something interesting happened in the remote stub. |
| |
| <p>The remote stub may send notification <var>name</var>:<var>event</var> |
| at any time, but <span class="sc">gdb</span> acknowledges the notification when |
| appropriate. The notification event is pending before <span class="sc">gdb</span> |
| acknowledges. Only one notification at a time may be pending; if |
| additional events occur before <span class="sc">gdb</span> has acknowledged the |
| previous notification, they must be queued by the stub for later |
| synchronous transmission in response to <var>ack</var> packets from |
| <span class="sc">gdb</span>. Because the notification mechanism is unreliable, |
| the stub is permitted to resend a notification if it believes |
| <span class="sc">gdb</span> may not have received it. |
| |
| <p>Specifically, notifications may appear when <span class="sc">gdb</span> is not |
| otherwise reading input from the stub, or when <span class="sc">gdb</span> is |
| expecting to read a normal synchronous response or a |
| ‘<samp><span class="samp">+</span></samp>’/‘<samp><span class="samp">-</span></samp>’ acknowledgment to a packet it has sent. |
| Notification packets are distinct from any other communication from |
| the stub so there is no ambiguity. |
| |
| <p>After receiving a notification, <span class="sc">gdb</span> shall acknowledge it by |
| sending a <var>ack</var> packet as a regular, synchronous request to the |
| stub. Such acknowledgment is not required to happen immediately, as |
| <span class="sc">gdb</span> is permitted to send other, unrelated packets to the |
| stub first, which the stub should process normally. |
| |
| <p>Upon receiving a <var>ack</var> packet, if the stub has other queued |
| events to report to <span class="sc">gdb</span>, it shall respond by sending a |
| normal <var>event</var>. <span class="sc">gdb</span> shall then send another <var>ack</var> |
| packet to solicit further responses; again, it is permitted to send |
| other, unrelated packets as well which the stub should process |
| normally. |
| |
| <p>If the stub receives a <var>ack</var> packet and there are no additional |
| <var>event</var> to report, the stub shall return an ‘<samp><span class="samp">OK</span></samp>’ response. |
| At this point, <span class="sc">gdb</span> has finished processing a notification |
| and the stub has completed sending any queued events. <span class="sc">gdb</span> |
| won't accept any new notifications until the final ‘<samp><span class="samp">OK</span></samp>’ is |
| received . If further notification events occur, the stub shall send |
| a new notification, <span class="sc">gdb</span> shall accept the notification, and |
| the process shall be repeated. |
| |
| <p>The process of asynchronous notification can be illustrated by the |
| following example: |
| <pre class="smallexample"> <- <code>%Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;</code> |
| <code>...</code> |
| -> <code>vStopped</code> |
| <- <code>T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;</code> |
| -> <code>vStopped</code> |
| <- <code>T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;</code> |
| -> <code>vStopped</code> |
| <- <code>OK</code> |
| </pre> |
| <p>The following notifications are defined: |
| <p><table summary=""> |
| <tr align="left"><td valign="top" width="12%">Notification |
| </td><td valign="top" width="12%">Ack |
| </td><td valign="top" width="38%">Event |
| </td><td valign="top" width="38%">Description |
| |
| <p><br></td></tr><tr align="left"><td valign="top" width="12%">Stop |
| </td><td valign="top" width="12%">vStopped |
| </td><td valign="top" width="38%"><var>reply</var>. The <var>reply</var> has the form of a stop reply, as |
| 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>, |
| for information on how these notifications are acknowledged by |
| <span class="sc">gdb</span>. |
| </td><td valign="top" width="38%">Report an asynchronous stop event in non-stop mode. |
| |
| <br></td></tr></table> |
| |
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| |
