Realtime implementation in EMC

[ChandlerBing]

Hello,

Going through the manuals, it is stated that HAL uses RTAPI for real time implementation. I am intrested to look into how HAL interfaces with real time implementation. What part of code does that and how is it achieved.

Can anyone guide me with some tips, pointers to such things

Kind Regards

[unterhaus]

RTAPI is a wrapper that works with RTAI ( or some older version of rt-linux)

Most people are using RTAI, because rtlinux went commercial and has virtually no support unless you buy the commercial version. If you want to develop your own real-time program, your best bet is to look up RTAI and learn from them. There are a lot of projects that use RTAI. The RTAPI part of emc is very nice, you can check out the emc code from cvs and work through the pieces. Halcmd would be a good place to start.

[david_geng]

I think there was a discussion regarding RTAI vs Xenomai vs rt patch to the kernel. Is EMC considering other two options?

[Seb]

Jeff Epler tried the -rt kernel in Gutsy Gibbon here. The short of it is it works but latency is a bit worse than RTAI, he was getting about 32 us and concluded that it would probably work if stepgen and/or pwmgen were offloaded onto dedicated hardware (such as a Gecko or a Mesa card).

[unterhaus]

Originally Posted by david_geng I think there was a discussion regarding RTAI vs Xenomai vs rt patch to the kernel. Is EMC considering other two options?

My impression is that they have the same API, so they are compatible. Haven't heard of anyone that wants to change kernels though.