[Tinyos-2-commits] CVS: tinyos-2.x/doc/txt tep113.txt,1.9,1.10

[Phil Levis]

Update of /cvsroot/tinyos/tinyos-2.x/doc/txt
In directory sc8-pr-cvs10.sourceforge.net:/tmp/cvs-serv827

Modified Files:
	tep113.txt 
Log Message:
Add Ben's comments.


Index: tep113.txt
===================================================================
RCS file: /cvsroot/tinyos/tinyos-2.x/doc/txt/tep113.txt,v
retrieving revision 1.9
retrieving revision 1.10
diff -C2 -d -r1.9 -r1.10
*** tep113.txt	6 Feb 2007 05:54:27 -0000	1.9
--- tep113.txt	29 Mar 2008 01:05:45 -0000	1.10
***************
*** 279,282 ****
--- 279,301 ----
  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 reliability: 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 contro transmissions.
+ 
  
  3.4 Dispatcher: SerialDispatcherC