[etherlab-users] Alternating working count 0/24 (zero and complete)

[J. van der Wulp]

Hello,

A lot more experiments further now. My findings:

Tcpdump and wireshark based observations with as well the 1.4 as the
1.5.2 version of the IGH EtherCAT master:
 - when a frame exceeds the 128 byte threshold then increasingly often
the latency of the response frame increases (seems a 100microsecond
offset) but our time budget (time between send() and receive()) is 100
microseconds. This is the cause for working count 0 errors.
 - as long as the process data is such that frame size stays below ~128
bytes there is no problem, the working counts stay stable and response
latency is more or less constant

Kernel observations:
 - clock_nanosleep wake up latency (measured with cyclic test) is
similar for the two kernels
 - the 1.5.2 version of the master on the 2.6.29 kernel with rt-preempt
running at 5Khz with 97 bytes of process data runs just fine ;-)
 - the 1.4 version with the the r8169 driver from 1.5.2 running on
3.4.97 rt-preempt has the same problems as the 1.5.2 version of the
master on the same kernel running at 5Khz with 97 bytes of process data
 - use the generic module when operating at 5Khz (only tested with 1.5.2
with frame size less than ~128 bytes) gives the same working count 0
symptoms, for our application we really seem to need the patched drivers...

Use of the IGH EtherCAT Master user library:
 - ecrt_master_set_send_interval was not present in our application
software so the EtherCAT-OP thread was running at 1Khz instead of the
5Khz of the real-time thread. This is not critical right?
 - in some experiments the extra datagrams injected by the EtherCAT-OP
thread were driving the frame size higher than the ~128 bytes boundary,
causing problems at 1Khz...

In summary, I now think that we have a problem with the r8169 Realtek
driver or modified Linux behaviour which increases the latency of
delivery of ethernet frames.

Best,

-- 



Jeroen van der Wulp

Software Designer

___________________________________________________________


Sioux. Source of your Technology
Technical Software | Electronics | Industrial Mathematics | Remote Solutions

Sioux Embedded Systems B.V.  |   Esp 405   |   5633 AJ Eindhoven   |
Nederland
T  +31 (0)40 2677100  |  jeroen.van.der.wulp at sioux.eu  |  www.sioux.eu