FSUIPC Offsets Update Frequency

[ark1320]

Hi Pete,

In general, does FSUIPC update offset values (such as airspeed, altitude, flight control positions, radar altitude, etc) from FSX at the sim rate (about 18Hz), or only when a particular offset is accessed via one of the ipc.read commands, or perhaps only when FSUIPC detects an offset value has changed?

Thanks,

Al

[Pete Dowson]

2 hours ago, ark1320 said:

In general, does FSUIPC update offset values (such as airspeed, altitude, flight control positions, radar altitude, etc) from FSX at the sim rate (about 18Hz), or only when a particular offset is accessed via one of the ipc.read commands, or perhaps only when FSUIPC detects an offset value has changed?

They are updated when SimConnect sends a new value which differs from the last one by enough to affect the offset. How often it sends them probably varies quite a bit according to which sub-system they come from.

If FS9 days (and before), FSUIPC used to grab the values from all over FS, directly from its assorted DLLs, on a "polling" basis at regular intervals -- basically at an internal sim rate or at the frame rate (depending on the values).

Since SimConnect was implemented, in FSX, it takes advantage of the SimConnect facilities.  Those supplying data for most of the types of offsets you are thinking about are only requested once on a "please supply when changed by more than x" basis. The updated values then just arrive whenever SimConnect decdes to send them.

Pete

 

 

[herve_sors]

Quote

only requested once on a "please supply when changed by more than x" basis. The updated values then just arrive whenever SimConnect decdes to send them

Interesting Pete..is "x" defined by FSUIPC on some predefined criteria you set in the code (may be depending on retrieved data) or by SimConnect itself and what does decides mean on the SimConnect side?

 

[Pete Dowson]

Just now, herve_sors said:

is "x" defined by FSUIPC on some predefined criteria you set in the code (may be depending on retrieved data)

SimConnect allows me to set 'x' individually for each data request. It cuts down on the traffic to/from SimConnect by only asking for changes which would be noticeable.  This value is per data request, so, yes, it will vary according to the data requested.

'x' is called the "epsilon" by SimConnect, and actually, by default, FSUIPC does these days default it to zero for all values. But there is an FSUIPC INI parameter which will make FSUIPC use different values for each value (with 'x' decided by my judgement about reasonable desirable precisions). Maybe it would help in those installations which have several SimConnect users clamouring for data and gradually clogging the interface up.

This option is documented in the Advanced User's guide, thus:

 

UseEpsilon is normally omitted altogether. If needed, it can be added, in the [General] section of the INI file, set to “Yes”. This will
impose change limitations on most variables sent to FSUIPC by SimConnect

Pete