This is an old thread but can still be hit so thought i would make a contribution about Shared Variables dropping out (reportng a zero).
I have good experience using Shared Variables (SV's) and have always noticed when the Windows side is busy (100% CPU load) the SV's sometimes drop out (report zero) for a short while whilst the RT side will not drop out and the SV's will continue to work as they should.
This is with the SVE (Shared Variable Engine) hosted on the RT target.
When designing realtime systems its always best to host the SVE in the RT target (if you arent hosting over a network to other systems) and ensure your RT application does not require any critical SV information from Windows. And vice versa; your Windows application shouldnt be logging SV's (otherwise expect zeros from time to time).
Get Windows to FTP a file from the RT and (sometimes) the SV's on the Window side will drop out - classic.
The above is more common in Hypervisor systems where resources are shared.
