Leopold Palomo-Avellaneda wrote: > ... > Ok, > > thanks for the answer. I have to addmitt that to me all the documentation is > a > bit confuse for someone that begins in this area. Although there are a lot > documents, I'm a bit lost.
That's what we are gradually trying to improve via the wiki. Work in progress, contributions of any form are welcome. > > My configuration is a normal PIII 550 with a rtai + rtnet and two ethernet. > One to our lab and another to a stäubli controller. Both have a 100Mb card > and are connected with a cross cable. > > If I unload the rtnet and I load the normal driver and I do a simple ping of > 200 bytes I obtain this values: > > [EMAIL PROTECTED]:~$ ping -s 200 192.168.1.4 > PING 192.168.1.4 (192.168.1.4) 200(228) bytes of data. > 208 bytes from 192.168.1.4: icmp_seq=1 ttl=64 time=0.567 ms > .... > .... > 208 bytes from 192.168.1.4: icmp_seq=48 ttl=64 time=0.523 ms > .... > 208 bytes from 192.168.1.4: icmp_seq=88 ttl=64 time=1.07 ms > ...... > 208 bytes from 192.168.1.4: icmp_seq=101 ttl=64 time=0.529 ms > .... > 208 bytes from 192.168.1.4: icmp_seq=140 ttl=64 time=0.540 ms > ..... > > --- 192.168.1.4 ping statistics --- > 158 packets transmitted, 158 received, 0% packet loss, time 157009ms > rtt min/avg/max/mdev = 0.488/0.598/1.159/0.169 ms > > after ifdown, unload the module and loading the rtnet then: > > ulises:/usr/local/rtnet# sbin/rtping -s 200 192.168.1.4 > Real-time PING 192.168.1.4 200(228) bytes of data. > ..... > 208 bytes from 192.168.1.4: icmp_seq=9 time=2547.4 us > .... > 208 bytes from 192.168.1.4: icmp_seq=24 time=3415.0 us > .... > 208 bytes from 192.168.1.4: icmp_seq=38 time=4722.8 us > ..... > 208 bytes from 192.168.1.4: icmp_seq=45 time=5356.8 us > > --- 192.168.1.4 rtping statistics --- > 45 packets transmitted, 45 received, 0% packet loss > worst case rtt = 8016.3 us > > > could someone explain me this, because I understand that us are micro second > (10^-6) so, this is worst in rt than in a normal net. If you picked the default setup via rtnet.conf, TDMA was activated at a cycle period of 5 ms, one transmission slot per node and cycle. Thus you get a latency of up to 2 x 5 ms. You can improve this by reducing the period or adding more transmission slots per cycle. If you only want to use the RTnet link for RT traffic and you have a collision-free media (cross-link or switched Ethernet), you could also run RTnet without RTmac/TDMA. Writing a specialised RTmac discipline (as a replacement for TDMA) is yet another option, but surely a more complex one. However, it all melts down to scheduling your network traffic for hard real-time use, not to make it simply as fast as possible, but to make it fully predictable. Jan
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