Finalized.

[tinyos-2.x.git] / doc / html / tep113.html

diff --git a/doc/html/tep113.html b/doc/html/tep113.html
index 7f502393fb108de40b26afc143df3c4660406c59..4bcc3f8000016441b8e28fffe038a2a0fbe9329b 100644 (file)
--- a/doc/html/tep113.html
+++ b/doc/html/tep113.html
@@ -291,19 +291,11 @@ ul.auto-toc {
 <tr class="field"><th class="docinfo-name">Type:</th><td class="field-body">Documentary</td>
 </tr>
 <tr><th class="docinfo-name">Status:</th>
-<td>Draft</td></tr>
+<td>Final</td></tr>
 <tr class="field"><th class="docinfo-name">TinyOS-Version:</th><td class="field-body">2.x</td>
 </tr>
 <tr><th class="docinfo-name">Author:</th>
 <td>Ben Greenstein and Philip Levis</td></tr>
-<tr class="field"><th class="docinfo-name">Draft-Created:</th><td class="field-body">11-Jul-2005</td>
-</tr>
-<tr class="field"><th class="docinfo-name">Draft-Version:</th><td class="field-body">1.9</td>
-</tr>
-<tr class="field"><th class="docinfo-name">Draft-Modified:</th><td class="field-body">2007-02-06</td>
-</tr>
-<tr class="field"><th class="docinfo-name">Draft-Discuss:</th><td class="field-body">TinyOS Developer List &lt;tinyos-devel at mail.millennium.berkeley.edu&gt;</td>
-</tr>
 </tbody>
 </table>
 <div class="note">
@@ -529,6 +521,23 @@ may be slightly delayed. However, acknowledgement information is
 stored in a queue separate from the data buffer, so a data packet to
 be transmitted may begin spooling into SerialP while SerialP is
 actively sending an acknowledgement.</p>
+<p>Only the PC-to-mote communication path supports acknowledgements.
+SerialP does not request acknowledgements from the PC for two reasons.
+First, acks are not perfect reliable: they are used on the
+PC-to-mote path to raise reliability to a usable level. In the case of
+the PC-to-mote path, the UART receive buffer is typically a single
+byte, so a high interrupt load can easily lose (and sometimes does) a
+byte. This is in contrast to the PC receive buffer, which is much
+larger and does not have to deal with overflow. Second, adding support
+for acks would increase the code size and complexity of the serial
+stack. As code space is often at a premium, this would add little
+needed functionality at significant cost. Of course, any application
+that requires perfect reliability may layer its own scheme on top of
+the serial protocol.</p>
+<p>The acknowledgement protocol is stop-and-wait to minimize buffering on
+the mote side. This is considered more important on memory constrained
+devices than increased throughput in the PC-to-mote direction, which
+most applications only use for occasional control transmissions.</p>
 </div>
 <div class="section">
 <h2><a id="dispatcher-serialdispatcherc" name="dispatcher-serialdispatcherc">3.4 Dispatcher: SerialDispatcherC</a></h2>