Mask TM parameter updates by VC
25/08/15 16:51 Filed in: New Features
It's now possible to selectively update different telemetry parameters from the same packet depending on the virtual channel they arrive on.
This feature can be useful for situations where we would like to maintain simultaneous sets of TM parameters for the same TM packet on different VC
One example use case is to separately visualise or monitor the same parameter from live and historical data (different VC) in parallel, even in the same display. Replaying TM from different VC on can cause confusion, especially if the two VC are in different time frames e.g. "live" and "recorded". A typical scenario might be that live TM and recorded TM are both downloaded in parallel during a satellite pass. It is important to separate these VC; for example if they are merged one might see large jumps in values, triggering delta limits merely because we are playing packets from different time frames.
Note: there are other ways to selectively play or replay different VC; this feature primarily adds the ability to maintain different copies of the same parameter from different VC simultaneously in the same session.
The feature is implemented by adding a new optional MIB field to the end of the PCF table; this field is called PCF_VCMASK. The mask can be any value from 0 to 255, each bit in the mask signifies the different possible Virtual Channels (0-7); using a mask may seem a little complicated but it allows selection of multiple VC. This is also same VC filtering approach used in the rest of the system. Examples: value 0 selects no VC, value 1 selects VC0, value 2 selects VC1, value 3 selects VC0 and VC1, value 4 selects VC2, value 128 selects VC7, value 255 selects all VC. The default VC mask is 255 which means there is no filtering by default.
You might typically define a packet with two sets of TM parameters from the same packet; these two different sets of parameters come from the same locations in the packet but each block has a different VC mask. The parameters have to have different names, but you can use a convention, e.g. a special suffix to indicate "historical".