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

[Razvan Musaloiu-E.]

Hi!

On Tue, 22 Apr 2008, Philip Levis wrote:

>
> 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?

I'm using Linux.

--
Razvan ME