User Documentation

Data recorder
System manual
2696790000/02/04.2020
84
● List of the stored samples of variables, consisting of variable ID and vari-
able value
All information is available as read only. They are stored in the profile buffer
before the application function call. For one thing, data fidelity is thus en-
sured, and for another thing, the intermittency of the recording is indepen-
dent of fluctuations that develop as a result of irregular run times of the appli-
cation function.
Information
The application function should have the shortest and the most constant
runtime possible. In the event that an automatic recording has been config-
ured for the profile, it must not contain any blocking calls, since unlimited
wait times have negative impacts on the recording of other profiles.
14.5 Data locality and real-time
The variable server concept, on which the data recording in profiles is
based, is defined across processes. That means that variables are physi-
cally distributed to different system processes. The determinism of data
recordings thus depends on the data locality: Access to process-local vari-
ables lasts shorter, while access to remote variables by means of interpro-
cess communication lasts longer.
In order to achieve the highest possible determinism for real time-relevant
recordings, process-local variables that are of a real-time quality should not
be registered in the same profile together with remote variables. In lieu of
this, it is recommended to separate profiles of a real-time quality – which
may possibly also scan in shorter cycles and higher priority – from the re-
maining profiles.
14.6 Size limitations
In consequence of the current technical implementation for 32 bit systems
(max. 4 GB virtual address space, max. 32 bit), the following theoretical limi-
tations apply in terms of the amount of data:
Max. buffer capacity Max. number of variables
524,288 1
262,144 2
131,072 4
65,536 8
32,768 16
16,384 32
8,192 64
4,096 128