On 06/08/2016 11:56 AM, Alex Plits wrote: > > >> -----Original Message----- >> From: Philippe Gerum [mailto:r...@xenomai.org] >> Sent: Thursday, June 02, 2016 4:12 PM >> To: Alex Plits; xenomai@xenomai.org >> Subject: Re: [Xenomai] XDDP NRT to RT communication and select >> >> On 05/11/2016 08:58 AM, Alex Plits wrote: >>> Hi, >>> >>> We require communication between non-real time and real time thread in >>> xenomai 3.x, so naturally we planned to use XDDP. >>> After careful read and looking into examples in smokey we tried to >>> implement simple communication Between NRT thread that sends via RTP >>> pseudo device a buffer to RT thread which is blocked on xenomai >>> "select" (read_fds) based on a ripped example of XDDP in smokey (without >> 2nd real time thread), i.e. NRT thread periodically sends messages to the RT >> thread waiting on select before actual receive call. >>> Unfortunately the "select" call on the RT thread was never triggered - >>> although in the smokey unit test it worked as expected, the only difference >> was the 2nd real time thread (which we got rid of in our case) used "sendto" >> call to that XDDP socket. >>> After some xenomai code examination we saw that XDDP send/recv >>> functions do signal xenomai select waiters which explains the smokey case >> (sendto triggered select) but It seems (correct me if I'm wrong) that >> xnpipe_write/read do not. >>> In order to confirm that we used "xnselect_signal" to trigger the xenomai >> select waiters in the "__xddp_input_handler" callback that is called inside >> xnpipe_write and this seemed to work. >>> So my queries are - >>> >>> 1. Does XDDP mechanism support select call for NRT writers - or did >>> we >> misread https://xenomai.org/2014/08/porting-a-linux-application-to- >> xenomai-dual-kernel/#IO_multiplexing_with_select? >>> >> >> That was the plan, but as you noticed, the implementation was broken, >> spuriously connecting the rt output to the rt input instead. >> >>> 2. Will the opposite direction work i.e. RT-> NRT that is waiting on a >> select? >>> >> >> Yes, this is a separate code path, which works fine. >> >>> 3. Is the small patch we added acceptable for the case described >>> above / >> is there any additional locking that we need to handle? >>> >> >> I don't know the exact implementation of your fix, but this should indeed >> live >> in the pipe input handler from the XDDP protocol module. >> Conversely, the corresponding code has to be removed from >> __xddp_sendmsg(). >> >> http://git.xenomai.org/xenomai-3.git/commit/?h=stable- >> 3.0.x&id=fd828bf38f2c7ba5140cbbf1ae932a5e184f823f >> > [Alex Plits] > Hi Philippe, > That seems to be the exact fix we have tried and indeed this solved the > select issue on the XDDP socket. > However this was part of our requirement - in addition to waiting on the XDDP > socket RT part, in the select call > we required a wait on a posix(RT) message queue descriptor and this yield > strange behavior, long story short - this does not work as expected although > using > select on each of them apart works fine. > i.e. > Select on the posix(RT) Qs -> works as expected > Select on the XDDPs after fix -> works as expected > Select on FD_SET where Posix(RT) Q descriptor is set and XDDP socket > descriptor is set -> broken. > >>From what we understand in the documentation mentioned in previous post this >>should work. > Can you advise?
Please send me a simple test case. -- Philippe. _______________________________________________ Xenomai mailing list Xenomai@xenomai.org https://xenomai.org/mailman/listinfo/xenomai
