[Tinyos-devel] CRC bug

[Andreas Koepke]

A 16 bit CRC can not detect all errors (no CRC check can). So once in a 
while a corrupt packet will pass the CRC check. If I remember correctly 
we observed that once in 50k packets, or so.

Roman Lim:
> A also get corrupt information, when i extract packet information 
> without using the serial stack. Until now, I did not spend a lot of time 
> finding the source of these errors.
> In my application, I only notice bad packets, when they contain 
> obviously wrong routing information.
> 
> Roman
> 
> Omprakash Gnawali wrote:
>> I have also seen a "few" bad node id's with CTP and default cc2420
>> stack in the past but no such incident in the recent experiments.
>> Sometimes, I also see corrupt packets (for example, pkts larger than
>> they should be). Are you sure what you are seeing is due to the radio
>> stack and not the serial stack? And not CTP or other pieces of
>> software that might be stomping on the pkt?
>>
>> - om_p
>>
>> On Jan 8, 2008 9:06 AM, Roman Lim <rlim at ee.ethz.ch> wrote:
>>> I did also observe wrong packets in a testbed with tmote sky nodes. the
>>> attached picture shows the network status after a 2.5 week testrun (ctp
>>> with low power mac). The red nodes at the bottom do not exist in the
>>> real network, but somehow their ids reached the visualization app.
>>> I am actually using a modified version of the current cc2420 stack, but
>>> I did not touch the crc check part in the CC2420ReceiveP.
>>>
>>> Roman
>>>
>>> David Moss wrote:
>>>> The continueRead() when the length shows a bad packet is supposed to 
>>>> read
>>>> out the RX FIFO as if it were a good packet, but the CRC should fail 
>>>> (65534
>>>> out of 65535 times) when complete.
>>>>
>>>> The S_RX_PAYLOAD is simply there to skip any kind of acknowledgement
>>>> checking.
>>>>
>>>> How many bad packets are you seeing, exactly?  And I wonder if 
>>>> anyone else
>>>> is having the same problem?  When I don't have CRC's enabled, I can 
>>>> really
>>>> tell a difference in the amount and types of packets received, 
>>>> especially
>>>> when my nodes are on the edge of communication.
>>>>
>>>> -David
>>>>
>>>>
>>>>
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