Reducing the Latency on a Bypass Function

Priority threshold in VXconfig

In VXconfig there is an option to define a value for a priority threshold. This value can be set between 0 (lowest priority) and 255 (highest priority).



All measurement signals bound to an XCP event channel with a higher priority than the priority threshold defined in VXconfig (here: 254), will be treated with high priority by the VX1000. While data bound to events with lower priority are buffered up to 20 ms, high priority data is sent immediately to the measurement and calibration tool (like for example CANape).

Priority of Bypass events in CANape

In CANape the XCP events with direction DAQ, which are used for bypass functions must have a higher priority than the priority threshold defined in VXconfig. The priority for each event can be set in the device configuration of CANape.

In this example the priority is set to 255 for all DAQ event channels which are part of a bypass. With the priority threshold set to a number smaller than 255 in VXconfig, these events will be handled with high priority in the VX1000 to achieve a low latency DAQ transfer for bypassing.

The priority of the event channels with direction STIM is of no importance for the VX1000 as this direction will always be handled with high priority

Note:

It is not advisable to also set DAQ events, which are used for measurement only, to high priority as this will have a big impact on measurement bandwidth, especially for fast event cycles with only a small number of measurement signals attached.



Article ID: 752
Last updated: 2020-04-17
Revision: 2
Hardware -> VX Hardware Family -> Reducing the Latency on a Bypass Function
https://kb.vector.com/entry/752/