[etherlab-users] Copley Drive w/ Distributed Clocks Drifting

[Graeme Foot]

Hi,

Just a couple of thoughts.

Does GetNsecHWClock read the time from your servo card?  Does the time
increment by 250000ns every period (ignoring jitter)?  Ie is your clock
time drifting with respect to the ISR?


I would try moving the get time and ecrt_master_application_time call to
just before the ecrt_master_send call.

The reason for this is that ecrt_master_application_time caches the time
value and then ecrt_master_send will send the time datagram without
making any adjustments to the time value.  So if theres any variance in
processing time between ecrt_master_application_time and
ecrt_master_send you will be creating a jitter in the time the slave is
reading.  (There is already enough jitter just with ecrt_master_send.)

eg:

void PhaseISR()
{
  static time

  ecrt_master_receive
  EC_READs

  ServoLoopCalcs()

  EC_WRITEs
  Ecrt_domain_queue

  HWClock = GetNanosecHWClock()
  if(init_time)
  {
    clockgettime(&time)
    init_time = 0
  }
  else
  {
    time += HWClock  - HWClockOld
  }
  HWClockOld = GetNsecHWClock()
  Ecrt_master_application_time(time)
  Ecrt_master_sync_reference_clock
  Ecrt_master_sync_slave_clocks(pshm->ECAT[idxMaster].Master)

  Ecrt_master_send
}


What type of slave is being used as the slave reference clock?  I have a
Beckhoff CX1020 with a built in coupler (CX1100-0004) with a 32bit dc.
I found that if this was the reference slave my yaskawa amps did not
like syncing to it.  I changed my reference slave to an EK1100 coupler
(64bit dc) and things are much more stable.


I don't know if this will make any difference but try reversing
ecrt_master_sync_reference_clock and ecrt_master_sync_slave_clocks.
This may (or may not) let the reference slave propagate a more stable
time to the rest of the slaves before receiving the updated time from
the master.


Regards,
Graeme.

-----Original Message-----
From: etherlab-users-bounces at etherlab.org
[mailto:etherlab-users-bounces at etherlab.org] On Behalf Of Henry Bausley
Sent: Wednesday, 25 April 2012 09:46
To: etherlab-users at etherlab.org
Subject: [etherlab-users] Copley Drive w/ Distributed Clocks Drifting


I am working with Copley attempting to use Cyclic Synchronous Torque
Mode at 250usec. We have setup up the distributed clocks w/ Sync0_Cycle
as 250000 and assign activate at 0x330.

What is being seen on the scope is the time at which an EtherCAT frame
arrives eventually drifts into when the Sync0 signal occurs on the
slave.  When this occurs the motor glitches since the drive cannot
accept our torque command and provide feedback at this time.

The engineers at Copley were gracious enough to create a pair of outputs
so we could monitor something on the scope. Take a look at the video
clip it displays this better than I can explain it.

The lower signal rising edge occurs at SYNC0 time.  The upper signal is 
high while receiving an EtherCAT frame.

ftp://support.deltatau.com/DT-USA/Henry/CopleyEtherLAB.mp4


When we monitor the register 0x92C with
watch -n0 "ethercat reg read -p0 -tsm32 0x92c"
we see +/- 2000

Our code is virtually identical to the provided examples except it
operates in an ISR triggered by a custom servo card.

void PhaseISR()
{
  static time

  ecrt_master_receive
  EC_READs

  ServoLoopCalcs()

  HWClock = GetNanosecHWClock()
  if(init_time)
  {
    clockgettime(&time)
    init_time = 0
  }
  else
  {
    time += HWClock  - HWClockOld
  }
  HWClockOld = GetNsecHWClock()
  Ecrt_master_application_time(time)

  Ecrt_master_sync_reference_clock
  Ecrt_master_sync_slave_clocks(pshm->ECAT[idxMaster].Master)
  EC_WRITEs
  Ecrt_domain_queue
  Ecrt_master_send
}

My ISR has ~10usec of jitter.  I am using RTL8168B PCIe cards with a
PowerPC AMCC460EX 1Ghz CPU.  

I don't have the setup in my hands but will be receiving it in a few
days.

Any ideas would be greatly appreciated!!!!!





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