[Tinyos-devel] lost packets from PC to the mote

[Philip Levis]

On Apr 21, 2008, at 12:06 PM, Razvan Musaloiu-E. wrote:
> Hi!
>
> On Mon, 21 Apr 2008, Andreas Koepke wrote:
>
>>>> 2. Due to the temperature dependency of the uC clock speed it may  
>>>> happen
>>>>   that the baud rate error is sometimes slightly too large for  
>>>> reliable
>>>>   communication. This cause is less likely with slower baud rates
>>>>   (they have a smaller initial error).
>>>
>>> If this would be the case then the losses should happen even if  
>>> there are
>>> no packets from the mote to the PC, right? From my tests there are  
>>> no
>>> losses in that case though.
>>
>> Correct, now for a little math: At 115200 Bit/s the uC has 86us to  
>> process
>> each byte.
>
> 115200 bits = 14400 bytes and 1/14400 is about 7e-05. So the MCU has
> around 70us to deal with each byte.
>
>> If both directions are used, this drops to 43us. Scheduling a timer
>> takes about this much in T2. So if the node happens to do something  
>> else
>> than mere byte crunching, packets may be lost.
>
> This situation should be indicated by some overflow register from  
> MSP420,
> right?

If I recall correctly, Ben's conclusions after a lot of experiments  
were:

1) You do not observe the overflow bit on the control register
2) It only happens with Cygwin and not with Linux

Observation 2 led him to shelve the issue.

Razvan, are you using Cygwin or Linux? Ben, am I a recalling correctly?

Phil