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

Chieh-Jan (Mike) Liang cliang4 at cs.jhu.edu
Mon Mar 2 06:41:13 PST 2009


One question for people who are using 57600 with C serial forwarder.  
Is it always reliable for you? Or, just "more" reliable than 115200?  
In my case, 57600 didn't solve the "write fail" problem, and I had to  
add some code to make it reliable for me.

Thanks

Mike

On Feb 18, 2009, at 4:48 PM, Philip Levis wrote:

>
> On Feb 17, 2009, at 9:14 PM, Jorge Ortiz wrote:
>
>> On Tue, Feb 17, 2009 at 5:42 PM, Philip Levis <pal at cs.stanford.edu>
>> wrote:
>>
>> 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 was actually using the b6lowpan stack on telosb and epic in Ubuntu
>> 8.04 and 7.10 and the mote->pc had corrupted packets and random
>> drops that caused several things to happen:
>>
>> 1)  The ip-driver code was timing out because the mote was not
>> successfully acking control packets sent from the driver to the
>> mote  (Stephen will can fill in the details here)
>
> Right -- this makes sense given the prior comments on failure cases.
> When the mote is sending as quickly as possible, it's hard to get it
> to receive packets.
>
>> 2)  When/if the ip-driver was successfully started, packets that
>> came in on from the mote were getting corrupted or dropped when they
>> were being forwarded from the mote to the PC, so none of the motes
>> were able to associate with the base mote and get IP addresses, etc.
>
> This is different. Mote->PC packets were being corrupted? That is very
> strange. The mote rate-limits itself. This sounds more like the issue
> that David Moss raised on the FTDI driver or USB hubs. Were they
> corrupted at the serial forwarder? This could be something like a DCO
> calibration issue...
>
>> Any decision that's made it more or less fine with me, except i
>> think it should be noted that the fast rate does cause reliability
>> problems with serial communication on telosb.  Generally I'd rather
>> have something work at a slower rate (and have those who know the
>> details of the stack make their own adjustments to speed up the
>> communication) than to have the unreliable serial communication make
>> the application not work at all.
>
> From an "I need to get this working" standpoint, you're completely
> right. 57600 is the right thing for you to do. From a system design
> and implementation standpoint, though, you want to figure out what the
> actual problem is and fix it. If the answer is that the only way to
> fix it is to switch to 57600, that's one thing; if it turns out
> there's a bug in the stack or toolchain, we should fix it.
>
> Phil
>
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