Re: [Emc-users] Prempt RT --> RTAI, Xenomai, delay

[Nicklas K. <nic...@gm...>]

> ...
> That's because NOBODY (manufacturers or distributors) wants to futz with 
> testing motherboard latencies, problems with their obsolescence, IO 
> boards, controllers, USB issues, etc. All that is a big concern to 
> anybody who wants to see LinuxCNC as part of their business.

Preempt RT do not manage priorities properly for interrupts while RTAI and Xenomai do. It is rather simple, execution time to service an interupt every now and then will delay real time tasks with as much time as they take to execute. Then there are SMI which will interrupt anyway. I run control loop at micro controller at 40kHz and it works perfect because it allow nested interrupts with priority.

> ...

> In addition, I believe that linuxCNC needs to be split into two parts 
> and "sold as such" by default:
> - headless LinuxCNC with hard RT kernel to run on different SBCs to 
> handle all CNC IO

There are cheap development board with micro controllers available. Most of them use some kind of Cortex-* CPU with an NVIC for nested interrupts with priority which is really great for real time even though they have a lot less computing power avaiable than an ordinary computer.

I would suggest to investigate possibility to separate code so that the real time tasks could be run on an micro controller. There also development boards available with extra ram so that they can run Linux, maybe even X11 would be possible.

> - GUI frontend, local or remote, connected to Linux workstation or 
> modern tablet over USB, ethernet, or WiFi. Countless digital tablets can 
> be had for under $100 that could serve as CNC UI.

GUI could stay on ordinary computer while real time taska move to cortex-* micro controller, they talk via TCP/IP and maybe even X11.

> ...


Nicklas Karlsson