Re: [RTnet-developers] multicast support

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

Amine El hedadi schrieb:
> I need to use rtnet for audio & video streaming , so i want to add support for 
> multicasting to rtnet.
> Now im trying to understand the working of mutlicasting in linux kernel, and i 
> look for the way to port it to rtnet.  
> So if you have any propositon to do that , please let me know.
> 

Beyond the aspect of how to manage rtskbs (RTnet's real-time packet 
buffers) for which I already posted a mail thread link, you should 
certainly first start with multicast at Ethernet level. First, you need 
support in at least one driver. Pick one and extend (or re-enable) its 
multicast features. Watch out for potentially required hard real-time 
synchronisation means between transmission/reception handlers and 
multicast manipulation functions. Feel free to ask what to use or how 
certain things work inside the driver.

Next, it's likely useful to add the required API to the packet socket 
interface (stack/packet/af_packet.c). That API has to provide means for 
registering to and detaching from a multicast group at Ethernet protocol 
level. Check Linux man pages etc. for documentation.

Later, the integration in RTnet's UDP/IP stack can be addressed. Here, 
the question needs to be answered how to map the multicast IP address on 
Ethernet MAC addresses. Not sure right now how this happens in normal 
networks, but I guess a static configuration is likely the easiest way 
for a first approach in RTnet.

Looking forward to further discussions! I'm also interested in learning 
more about multicast implemenation and potential hard real-time issues.

Jan