Hello, as I told you, I don't want to insist in this point because it
seems to be annoying you, if it is not possible to know when the
packet has arrived and nobody can send any clue on how to do it, we
will find another solution to our problem.
Thank you very much to everybody.
Best regards.
Quoting Richard Hacker <h...@igh-essen.com>:
Hello,
Please let me put things straight: there is no way of knowing when
an EtherCAT
packet has arrived, because there is *NO need to*!!!!
Digital computer controlled systems are sampled data systems with
one inherent
delay cycle from input to output. They are not analog computers. In the limit
when the cycle time tends to zero they start to *look like* analog computers.
Where this limit is depends on your application!
So, normal controllers running EtherCAT do:
calculate;
exchange io;
wait;
calculate
exchange io;
wait;
... till the end of time
Inside "exchange io", data from the calculation is output to the
slaves and AT
THE SAME TIME the input slaves are sampled (ecrt_master_send() ).
These inputs
wait until the next calculation step before they get processed.
Inside calculate, ethercat data frames are fetched from the ethernet card
(ecrt_master_receive() ), processed for inputs (which were fetched while the
program was sleeping) (ecrt_domain_process() ), running your control
algorithm, and queuing the outputs from your controller (ecrt_domain_queue()
). The important thing to note, is that the ethercat frames must be
waiting on
the ethernet card before the master is requested to fetch them, otherwise the
master will puke and think the frame was lost. Thus fetching data too early
before the frame has arrived will get you into trouble. That is why
it is VERY
IMPORTANT to sleep after "exchange io".
If this concept does not suit your timing requirements, then EtherCAT is not
your solution - you need directly attached IO where you can synchronously
sample inputs, calculate and write outputs. Just before giving up on
EtherCAT,
it has been tested at rates to 10kHz ;)
Oh by the way, we and many others have been working successfully
with EtherCAT
on a number of not so small applications for a few years without needing
synchronous IO.
- Richard
On Wednesday 19 October 2011 10:52:03 Jordi Blanch Carles wrote:
In our case, the whole EtherCat loop would be:
ask_for_inputs() <----- ecrt_domain_queue + ecrt_master_send
wait_for_packet_received()
process_inputs() <----- ecrt_master_receive + ecrt_domain_process
make_calculations()
send_outputs() <----- ecrt_domain_queue + ecrt_master_send
wait_for_next_period()
Mit freundlichem Gruß
Richard Hacker
--
------------------------------------------------------------------------
Richard Hacker M.Sc.
richard.hac...@igh-essen.com
Tel.: +49 201 / 36014-16
Ingenieurgemeinschaft IgH
Gesellschaft für Ingenieurleistungen mbH
Heinz-Bäcker-Str. 34
D-45356 Essen
Amtsgericht Essen HRB 11500
USt-Id.-Nr.: DE 174 626 722
Geschäftsführung:
- Dr.-Ing. S. Rotthäuser,
- Dr.-Ing. T. Finke,
- Dr.-Ing. W. Hagemeister
Tel.: +49 201 / 360-14-0
http://www.igh-essen.com
------------------------------------------------------------------------
Jordi Blanch Carles
Unidad de Ensayo y Control
ENCOPIM S.L.
C/. del Parc, 5 (nave 13)
P.I. Els Pinetons
E-08291 RIPOLLET (Barcelona)
Tel: (+34) 935 94 23 47
Fax: (+34) 935 94 64 15
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