[etherlab-users] Problems with Pdo entry with index 0x0000

[Richard Hacker]

You have to add the gaps to the configuration but you cannot map them to 
a variable! I think you are confusing configuration and mapping.

Configuration is done using ecrt_slave_config_pdos() to inform the 
master how the slave PDO is constructed. This configuration may include 
gaps which are used to align PDO's to natural borders.

However, gaps can not be mapped to a process variable inside your 
program i.e. with ecrt_domain_reg_pdo_entry(). That means you can not 
access the values in these gaps.

Thus I was wrong last time. Since ecrt_domain_reg_pdo_entry_list() can 
only access real PDO's (having a non-zero index), the functionality 
inside the master is correct.

- Richard


Am 11/06/2013 09:17 AM, schrieb Jordi Blanch:
> Hello,
>
> we thought that it was necessary to add GAPs entries to the list,
> otherwise the master couldn't calculate the bit offset of the data
> received from ethercat frames because every ec_pdo_entry_reg_t relates
> it's data position to the previous ec_pdo_entry_reg_t item, isn't it?
> Also, I think I remember we already tried not to register GAPs and then
> we were not receiving the data correctly (but I'm talking from my
> memory...).
>
> Thank you.
>
> On Tue, 5 Nov 2013 17:48:03 +0100, Florian Pose <fp at igh.de> wrote:
>> Hello,
>>
>> On Tue, Nov 05, 2013 at 04:36:26PM +0100, Richard Hacker wrote:
>>> I understand your problem when registering gaps. Actually the code
>>> in the ethercat master does not do the right thing by testing on
>>> index. Actually it should be testing for reg->bit_position instead.
>>> I will communicate this with the developer.
>>
>> sorry Richard. I have to be contradictory. ;-)
>>
>> Please let me clarify this: There should be no gaps in the list passed
>> to ecrt_domain_reg_pdo_entry(), because gaps are no actual PDO entries
>> and can not be uniquely identified via PDO entry index and
>> subindex, and thus can not be registered.
>>
>> Note that gaps are perfectly valid in context of the PDO configuration
>> (see ecrt_slave_config_pdos() and friends).
>>
>> Best regards,
>> Florian
>> _______________________________________________
>> etherlab-users mailing list
>> etherlab-users at etherlab.org
>> http://lists.etherlab.org/mailman/listinfo/etherlab-users
>

Mit freundlichem Gruß

Richard Hacker

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