:TEP: 113
:Group: Core Working Group
:Type: Documentary
-:Status: Draft
+:Status: Final
:TinyOS-Version: 2.x
:Author: Ben Greenstein and Philip Levis
-:Draft-Created: 11-Jul-2005
-:Draft-Version: $Revision$
-:Draft-Modified: $Date$
-:Draft-Discuss: TinyOS Developer List <tinyos-devel at mail.millennium.berkeley.edu>
-
.. Note::
This memo documents a part of TinyOS for the TinyOS Community, and
be transmitted may begin spooling into SerialP while SerialP is
actively sending an acknowledgement.
+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.
+
+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.
+
3.4 Dispatcher: SerialDispatcherC
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