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

[Razvan Musaloiu-E.]

Hi!

On Mon, 21 Apr 2008, Andreas Koepke wrote:

> Just my 2c:
>
> 1. according to the data sheet of the serial-to-USB converter of the
>    telos nodes, data rates above 38400 may not work reliably without
>    flow control. Not sure whether this is still true under all
>    circumstances.
>
> 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.

> 3. Can you cross-check with the C++ sf? In our experiments it does not
>    loose packets.

Here is what the C++ version says:
 	>> SF-Server ( SerialComm on device /dev/ttyUSB0 ) : baudrate = 115200 , packets read = 8958 ( dropped = 2678, bad = 0 ) , packets written = 106 ( dropped = 0, total retries: 46 )
The packets are not really dropped from the sf client point of view 
because the sf is retrying. The number of retries is very high though. :|

--
Razvan ME

> Best, Andreas
>
> Razvan Musaloiu-E.:
>> Hi!
>>
>> On Sat, 19 Apr 2008, Razvan Musaloiu-E. wrote:
>>
>>> Hi!
>>>
>>> On Sat, 19 Apr 2008, Vlado Handziski wrote:
>>>
>>>> It is a known behavior for which many hypothesis have been made, but no one
>>>> has nailed the bug/problem until now. You can dig through the  core WG notes
>>>> for some more info on the issues like the different preference to sending
>>>> mote->pc direction, etc. Ben has looked into this and it seems it is not a
>>>> queue overflow problem. He also experimented with making the ISR reentrant
>>>> without noticeable improvement.
>>> Thanks for the quick reply. I guess some of the notes you are talking
>>> about are these:
>>> 	http://tinyos.stanford.edu:8000/TinyOS_2.x_WG/05.16.2007
>>
>> Some more details: I run the same test code on micaz (on which the
>> baudrate is 57600) and no packets were lost. I also lowered the baudrate
>> to 57600 for telosb and it also stop losing packets. I only tested with
>> low (1 packet/s) data rates from PC to the mote.
>>
>> Question for Ben: did you also notice this?
>>
>> --
>> Razvan ME
>>
>>>> On Sat, Apr 19, 2008 at 3:47 AM, Razvan Musaloiu-E. <razvanm at cs.jhu.edu>
>>>> wrote:
>>>>
>>>>> Hi!
>>>>>
>>>>> I just noticed that when a mote sends a lot of packets to a the PC, the
>>>>> packets from the PC to the mote doesn't go reach the user application layer
>>>>> some of the time. In the attached archive there is a test program that is
>>>>> exposing this. The mote program is sending packets back-to-back while the PC
>>>>> program (in Java) is receiving the packets and sends to the mote one packets
>>>>> each second. I run the program on telosb in the following way:
>>>>>
>>>>> (console 1)$ ./sf 9001 /dev/ttyUSB0 115200
>>>>> (console 2)$ java StressSerialTest -comm sf at localhost:9001
>>>>>
>>>>> The mote is toggling the blue led each time it receives a packet and it
>>>>> should change state each time the RX led from the USB blinks. This doesn't
>>>>> always happen: the RX led indicates a receive but the blue doesn't always
>>>>> change its state. The (console 1) also shows lines like this:
>>>>>        Note: write failed
>>>>>        Note: write failed
>>>>>        Note: write failed
>>>>>        Note: write failed
>>>>>
>>>>> Did anyone else notice this behavior?
>>>>>
>>>>> --
>>>>> Razvan ME
>>>>>
>>>>>
>>
>