On Sat, Jan 5, 2013 at 12:49 PM, Peter Soetens <peter [..] ...> wrote:
> Hi Jonathan,
>
> Op vrijdag 4 januari 2013 schreef Johnathan Van Why (jrvanwhy [..] ...) het
> volgende:
>
>> We have a component that must run in realtime which sends out messages
>> that contain a vector. For reference, here is the relevant part of the
>> ROS message definition:
>>
>> uint8[] metadata
>>
>> To construct an instance of this message (of type "rt_ops_event") in a
>> realtime-safe manner such that adding elements to metadata is
>> realtime-safe, it appears as if the following will suffice:
>>
>> rt_ops_event_<RTT::os::allocator >
>
> That should have been RTT::os::rt_allocator...

Thanks -- I typo'd while writing my email, but I'm glad that that
statement is otherwise fine.

>>
>>
>> However, we are unsure if trying to send this message through an
>> OutputPort is deterministic. The Component Builder's Manual states
>> that if you do not give the port an example message of the maximum
>> size expected, then "data transfer will proceed, but the RTT makes no
>> guarantees about real-timeness of the transfer."
>
>
> This should be better defined. If you use a realtime allocator, the transfer
> will
> Always be realitme. So the above sentence assumed your data was using
> The standard allocator.

Thank you -- this makes things a lot easier for us.

>
>>
>>
>> The way we are using this message, we do not know what the largest
>> possible message size is when the component is initialized -- all we
>> can do is give it some constant size and hope it is enough, a solution
>> I find "unclean."
>>
>> For our purposes, we do not need the message to make it to the
>> receiving component in a deterministic manner, but the
>> OutputPort.write() call must be deterministic.
>>
>> Is OutputPort.write() always deterministic, even if the data transfer
>> itself isn't, or do we need to give it an example message?
>
>
> Yes and no. The rtt code itself is deterministic, the determinism of copying
> of your
> Data will depend on your allocator used. The sample data only
> Initializes rtt's internal data such that a next copy of a real sample
> Will not cause a memory allocation if it does not exceed the sample
> Size.
>
> In short, you don't need setDataSample if your data has a real-time
> allocator. But it will avoid calling your allocator if sizes are smaller,
> saving you some cycles....(but the time will always be bounded
> by your allocator)
>
> Peter
>
>>
>>
>> Thank you for any help,
>> Johnathan Van Why
>> Dynamic Robotics Laboratory
>> Oregon State University
>> --
>> Orocos-Users mailing list
>> Orocos-Users [..] ...
>> http://lists.mech.kuleuven.be/mailman/listinfo/orocos-users

Thank You,
Johnathan Van Why
Dynamic Robotics Laboratory
Oregon State University