Hi Anders,
On 09/02/2013 05:22 AM, Anders Wallin wrote:
> EtherCAT on the other hand seems to require special proprietary ASICs or
> NIC-chips? I am also guessing that to maintain low latency an EtherCAT
> switch is much more intelligent&expensive than a standard Ethernet switch.
Ethercat supports several common NICs, including r8169 (but not 8168!)
and e1000, both easily obtainable. The existing Linux drivers are
modified to add RT capabilities, I believe. I've been helping Sascha
Ittner (mentioned in a previous post) to port his work to LinuxCNC. He
recently updated the drivers to work with 3.5.7, so you have your choice
of Xenomai and RTAI kernel packages.
You're right that ethernet concentrators can be problems. A standard
ethernet switch will probably kill RT.
A better option is 10/100 (non-switching) repeater hubs, which instantly
repeat every packet to every port. Packet collisions (ah, takes me back
to the days of my youth!) will affect latency, but using a very small
fraction of total bandwidth will minimize this.
Best of all is to use a dedicated NIC and crossover cable for each device.
Right there is about all I know about RT over ethernet. :)
John
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