[Tinyos-devel] again about the baudrate issue for telos

Philip Levis pal at cs.stanford.edu
Tue Feb 17 17:42:11 PST 2009


On Feb 17, 2009, at 8:42 AM, Jorge Ortiz wrote:

> If we're taking a poll, I vote to slow it down to 57600.  I've had  
> trouble with the higher speed with and without the serial  
> forwarder.  At 57600 all my serial-related reliability problems went  
> away and the code I was working with was significantly more stable.
>
> Jorge

Can you be more specific than "I've had trouble?" Which direction?  
What motes? What operating system? Which serial forwarder?

I could have some code in my back pocket that's unstable except at  
2400. There's a fundamental issue here, with respect to rate control  
and flow control. The general operating model for the serial stack was  
that data mostly comes *out* of the network, so you want to optimize  
the mote->PC speed. Changing it to 57600 might make the problem go  
away for some cases, but it doesn't actually solve the problem. This  
isn't good system design.

Design by straw poll is generally fine, but polls can change with the  
winds. The last time there was a straw poll, the answer was 115200...

If you want to change the speed to 57600, you can always call the  
command on Msp430Usart1C. Or, shadow TelosSerialP.

Please note that changing the default will mean that all existing  
programs which assume 115200 will break. For example, if someone does  
a CVS update but doesn't recompile the toolchain, then serial at xx:telos  
will be 115200.

Phil



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