Leopold Palomo-Avellaneda wrote: > A Dimarts 20 Març 2007 15:00, Jan Kiszka va escriure: >> 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. > > a Readme first ...
What information are you missing in the existing top-level readme? > >>> 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. > > Ok, I only want a simple thing. The problem is that I need the fastest low > latency response as I can. I have only to send some bytes, no a lot of info. Then you probably want plain RTnet without RTmac/TDMA. > > You comment something about to modify the tdma.conf file. I have this > parameters: > > master: > ip 192.168.1.3 > cycle 5000 > slot 0 0 > slot 1 100 > > #slave: ^^^ This comments out the slave section mark, thus breaking the syntax. > ip 192.168.1.3 > #mac 00:C0:3A:25:01:OB > mac 00:A0:C9:1D:52:B9 > slot 0 2400 > slot 1 2200 2/2 > > but I don't know if this are correct or not. The fragment above is for demonstration of the tdma.conf language. See Documentation/README.rtmac for details about what those lines express. > >> 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. > > Yes I know, but is a simple system: a PC with rtai and rtnet and a robot > controller with vxworks. This doesn't tell anything about the communication structure, the timing of your system, or the closure of the control loop (if there is any). Jan
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