Re: [RTnet-developers] Suspect packet

[Jan K. <jan...@we...>]

Frank Tkalcevic wrote:
>>>
>>> It looks like a corrupt buffer, half sync packet, and half 
>> a config packet.
>> Not necessarily corrupted, but too long. Where and how did 
>> you capture this frame? 
> 
> The capture is from my embedded client.  The data transfers and packet
> length count is handled completely by the microcontroller, so I'm confident
> it is working correctly.  
> 
>> Does it fit into the TDMA cycle?
> 
> I don't fully understand rtnet to really answer that.  I started rtnet on my
> linux box, and it was waiting for slaves to connect.  Sync packets were
> coming out at the default 5000us interval as well as the rtcfg traffic
> (client config every 1000ms).  
> 
> I'm not sure why the sync packets were coming out as well as the rtcfg
> traffic.  Is that correct behaviour?  I would have thought the sync process
> would only happen after rtcfg set up was complete.

It is correct, RTmac/TDMA is in charge of managing the media access
right from the start (that's why RTcfg stage 1 frames have to include
all information a slave needs to send its own frames, namely the TDMA
cycle offset and phase).

BTW, Wireshark is capable of decoding RTnet frames, maybe helpful for
understanding the procedures.

> 
>>> This is coming from my master, a VIA Pico, with a via rhine 
>> ethernet 
>>> controller, using kernel 2.6.24-16-rtai (stock EMC2 deploy).  I 
>>> noticed that a comment in the rtnet rhine driver source say 
>> Rhine II, 
>>> but the board has a rhine III.  Could it be due to this?  
>> Or is this an undocumented packet?
>>
>> I guess the Rhine III is operated by the same driver as the 
>> II in standard Linux. Then is may make some sense to check 
>> the original code for diffs with our version, specifically 
>> for changes that target III support.
> 
> 
> Thanks, I'll check that.
> 

Additionally, you could instrument the driver to check what frame sizes
it receives from the upper layers and tries to send out. It's unlikely
that there is a bug at those levels, but who knows...

Jan