On 01/20/2014 05:18 PM, Leopold Palomo-Avellaneda wrote:
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.
You can both send-receive data to/from the same socket descriptor
RT-wise, and read-write from/to the same /dev/rtp* descriptor NRT-wise.
Message pipes are bi-directional by design, on both ends. In the XDDP
case, traffic is routed as follows:
- RT-writes -> NRT-reads
- RT-reads <- NRT-writes
So, fd = open("/dev/rtpX", ...) => read(fd, and write(fd, are allowed
s = socket(AF_RTIPC, ...) => sendmsg(s, and recv(s, are allowed.
--
Philippe.
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