Re: [Xenomai] xddp port questions

["Leopold Palomo-Avellaneda" <leo@alaxarxa.net>]

A Dimarts, 14 de gener de 2014, Philippe Gerum va escriure:
> On 01/14/2014 01:15 PM, Leopold Palomo-Avellaneda wrote:
> > Hi,
> >
> > in the example xddp-label a two realtime task are connected with a non-
> > realtime time. They share the same port where one rt task receive from the
> > non-rt task and the other send to rt-task.
> >
> > The regular thread read and write in the same devname
> > (/proc/xenomai/registry/rtipc/xddp/XDDP_PORT_LABEL). One rt thread listen 
from
> > that port.
> >
> > I don't understand how is possible that both (non-rt and rt threads) 
listen
> > from the same port and could not have collisions  if two threads (non-rt 
and
> > rt) try to write in the same port.
> >
> > Could not be better to separate it?
> >
> 
> No, that would defeat the purpose of the illustration.
> 
> XDDP is a wrapper over Xenomai's message pipe support, offering a 
> socket-based interface to applications. Each XDDP port is mapped to a 
> given /dev/rtp device minor, but the communication endpoints between RT 
> and NRT are different internally.
> 
> [XDDP-port] <---> xnpipe #<port>
>                       ^
>                       |
>                       |  * input queue:  /dev/rtp -> xnpipe
>                       |  * output queue: xnpipe -> /dev/rtp
>                       |
>                       v
>                 /dev/rtp<port>
> 
> So, when NRT reads from /dev/rtp<port>, it does not actually listen to 
> the same endpoint/queue than RT, because message pipes are 
> bi-directional. Likewise, NRT and RT never write to the same queue, 
> since the purpose of message pipes is to cross the RT/NRT domain boundary.

Ok,

in the example the same thread open a device for write and read from the same 
device. From your answer about the endpoints, I understand that when the NRT 
open for read, read from the RT world, and when the NRT writes to the RT 
world.

So, could I have a NRT function (thread) that open the device to just read 
from the RT world and _another_ that send to the RT world? 

Because I have to one the same device, and I don't know that I could do it at 
the same time.
 
Regards,

Leopold

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Linux User 152692
Catalonia
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