Hello Richard and others,
did anybody tried how low one can get with the sleep times in example
below without crashing server?
We are going (not there yet) to try to close motion control servo loop
over EtherCAT and ideally would like to see something like 1us
(microseconds) for the first delay and 250us for the second. Would you
consider that achievable (in case of less than 10 EtherCAT nodes) ?
Thanks and best regards to all,
Yan Prochazka
On 10/25/2011 03:44, Richard Hacker wrote:
OK here is a solution to your problem without changing EtherCAT
put all your input slaves into one domain and all your output domains in
another. Then
while (true) {
ecrt_domain_queue(input_domain);
ecrt_master_send();
sleep(1ms);
ecrt_master_receive();
ecrt_domain_process(input_domain);
ecrt_domain_process(output_domain);
calculate();
ecrt_domain_queue(output_domain);
ecrt_master_send();
sleep(39ms);
}
Finally, I would end the conversation if your reason for arguing is just
because "you don't really want to change the code", either because "you
don't get paid for it" or "you don't want to get back to old code" or "you
are too lazy" and we'd try to modify the drivers ourselves.
None of the above, except that time is a continuous deficiency on our side.
The issue is that cyclic tasks by nature are timer driven tasks, not interrupt
driven. These two models mix as good as oil and water. The master does not
react on network card interrupts.
If the input_domain has not come back by the time ecrt_master_receive() is
called, the master *will* puke and there is no way from stopping him from
doing so. That is by definition so, not by policy.
On the other hand, EtherCAT code is LGPL. You are free to modify the master in
terms of the Licence. That means that you are not allowed to break the
ethercat portion of the code in terms of the Beckhoff License (NOTE: NO new
thread on this point), but if you wish to change the master's response to
missing frames and ignore it if the master recons that the frame might not
have had the chance to be back by the time master_receive() is called, then
sleep a little longer or whatever, you can do it yourself.
Mit freundlichem Gruß
Richard Hacker
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