Prof. Max Fischer wrote: > Hi, > > I am using rtnet-0.9.5 with rtai3.3 on kernel 2.6.15. I would like to > implement an application using raw sockets with somewhat special > requirements: > There are situations where a few subsequent packets arrive very fast. > This means, that I would like to loop receiving already arrived packets. > Unfortunately, I only get one packet, subsequent receives time out. > > e.g., when I do > > send_packet (1) > send_packet (2) > recv_packet (3) > recv_packet (4) > > on a (hardware) loopback device, (3) is ok, but 4 times out (even after > a delay). After another send_packet, I get the packet from (2), but I'm > never able to recv all the packets that arrived. > I tracked down the situation and found out the following: > > In rt_packet_rcv (af_packet.c) > > after > > rtdm_sem_up(&sock->pending_sem); > > pending_sem->count doesn't increase with subsequent arriving packets. > This comes from pending_sem->type being a binary semaphore where I hoped > pending_sem might be counting. > As packets seem to be buffered correctly (when a new packet arrives > after a recv on my side, I get the right packet in the sequence), I > would like to ask, if this is a desired > behavior or if it would be a good idea to change pending_sem to be > counting (although RTDM doesn't offer counting semas in my opinion).
Yes, you re-confirmed a known RTAI 3.3 bug [1]. > > Any proposals? Did I get the situation wrong and there is a user level > solution? Would be changing pending_sem to counting be acceptable or > would it break something else? > Any help appreciated... I would suggest to update to 3.3-cv, or directly 3.4 (due to another RTAI issue with semaphore timeouts). With the 3.4 release and RTnet 0.9.5 you will run into this bug [2]. That one is now fixed in RTAI's magma CVS AFAIK. Jan [1]https://mail.rtai.org/pipermail/rtai/2006-March/014518.html [2]http://sourceforge.net/mailarchive/forum.php?thread_id=30604610&forum_id=24610
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