Data Transfer Suggestion

[TiTou]

Hi Doug,

Thanks alot for these explanations !

Just one more point, what, in your opinion, is the best way to transfert custom data type from RT to host ?

I was thinking that of TCP for periodical transfert
and dynamic calling from the host a VI that is running on the RT when waiting for a non-periodical event to send the datas

Does it seem correct to you ?

Thanks again for help 😉

[Doug M]

Depending on your application you may have to experiment to see what method gives you the best results, but if I were doing it I would use a communications loop that used the Shared Variable to transfer clusters -- this communication loop would also call the time critical loop.  This is the normal Real-Time/Host architecture.  I don't see any advantage to using TCP over the Shared Variable, but if latency concerns are great, you may need to experiment to see which method gives the best performance for your application.

[ashm01]

Hey Doug,

Like I had mentioned before, I am yet to migrate to LV8 on My RT system. However, I did implement the shared variables and a FTP solution which shall be tested when I finally migrate to LV8. I was curious about the shared variables, since I have multiple options like Fifo's, Networked published etc..my question is regarding the single process variables.

How will they differ from using FIFO's or FGV's, Is the same logic of FGV recreated in "Shared Variables". Eventually, the goal is to use the time critical thread to write to the shared variable and a normal priority to stream to a buffer and then a disk. Will I see less latency after LV8?

Regards,

Ashm01

[Doug M]

Ashm01,
The definitive white paper to Shared Variables can be found here.  This document includes benchmarks of Shared Variables versus other types of communication -- as for your exact scenario, it is difficult to say how much latency would be affected.  From the white paper, with less data/variables Shared Variables are somewhat slower, but as the number of variables/amount of data increases the performance is nearly asymptotic with other methods -- and Shared Variables are much much more simple to set up than TCP communication for instance.

Message Edited by Doug M on 01-13-2006 01:32 PM

Message Edited by Doug M on 01-13-2006 01:33 PM