[etherlab-users] Accessing same PDO for both read and write

[Yan Prochazka]

Hi Graeme,

thanks for the advices! We are going to try the "safe for real time" SDO 
approach.

However I have looked at ecrt_slave_config_reg_pdo_entry() 
implementation and adding some kind of Rx/Tx distinguishing flag should 
be relatively simple because sync_configs[] already know whether it is 
Rx or Tx. More work would be needed to make plumbing out of the kernel 
space though and moreover we would end up with Ethercat master code with 
our private changes with all the consequences for future updates.

Best Regards,
Yan

On 1/24/2013 16:02, Graeme Foot wrote:
> Hi,
>
> As another possible workaround (completely untested) you could try
> putting them in two separate domains. You might need to queue the read
> domain before the write domain to ensure you are reading the slave
> updated value rather than the newly written value.
>
> If this works, the write value can always be 1 which means you can
> re-arm the trigger in one cycle instead of two. Or you may need to only
> queue the write domain when you need to re-arm......
>
> Graeme.
>
> ------------------------------------------------------------------------
>
> *From:*Thomas Nelson [mailto:gcsnh at granitecomputersciences.com]
> *Sent:* Friday, 25 January 2013 04:01
> *To:* etherlab-users at etherlab.org
> *Cc:* Graeme Foot
> *Subject:* Re: [etherlab-users] Accessing same PDO for both read and write
>
> On Jan 23, 2013, at 11:21 PM, Graeme Foot wrote:
>
>
>
> Hi,
>
> I don't know the answer to the question, but as a workaround you could
> set up reading the value via PDO and write the value via an SDO. Writing
> via SDOs take approx 30ms for CoE.
>
> Regards,
>
> Graeme.
>
> ------------------------------------------------------------------------
>
> *From:*etherlab-users-bounces at etherlab.org
> <mailto:etherlab-users-bounces at etherlab.org>[mailto:etherlab-users-bounces at etherlab.org]*On
> Behalf Of*Thomas Nelson
> *Sent:*Thursday, 24 January 2013 16:15
> *To:*etherlab-users at etherlab.org <mailto:etherlab-users at etherlab.org>
> *Subject:*[etherlab-users] Accessing same PDO for both read and write
>
> All,
>
> My client has a robotics system using Copley Controls Accelnet Plus
> drives with a digital input-triggered capture capability that we're
> trying to use for positioning calibration. This feature requires the
> ability to map the same slave CoE object for both read to detect the
> capture event and write to subsequently rearm the trigger. Mapping this
> object to both Tx and Rx PDOs appears to work correctly from the PDO
> mapping info returned from the master. However, when I attempt to
> register the corresponding mapped PDO entries in the domain, I get the
> same domain offset for both PDOs, preventing the application from
> managing them independently.
>
> The ecrt_slave_config_reg_pdo_entry() function doesn't have an argument
> to distinguish the direction of the PDO mapping, so is this capability
> not supported by the master?
>
> We're using the 1.5.0 release.
>
> We had in fact discussed this as a possible alternative, but were
> concerned that the SDO latency (which we didn't know previously -
> thanks!) could prevent the trigger from being rearmed quickly enough to
> avoid missing a subsequent event at the target motion rates. The system
> uses optical sensors for this calibration that generate rising and
> falling edge events that must be detected, and the r/w object in
> question handles trigger rearming for both types of events.
>
> Best regards,
>
> Tom Nelson
> Consulting Engineer
> Granite Computer Sciences, LLC
> (603) 672-8525
>
>
>