Re: [realtime] Re: [rtl] virtual memory in RTL

[Stuart Hughes <sehughes@zentropix.com>]

yodaiken@fsmlabs.com wrote:
> 
> On Thu, Mar 23, 2000 at 03:44:51PM +0000, Stuart Hughes wrote:
> > I think you do misunderstand as what you describe could be a write up of
> > the latest LXRT.  The first LXRT was soft real-time, but the latest one
> 
> That's what I was thinking of.
> 
> > lets you switch to hard real-time from a user space process.  Once in
> > this mode you are restricted to RT only calls (as with RT modules), but
> 
> So you make RT calls via  "int something" ? How do you deal with
> the memory map? Does the RT system switch mmu context
> 
> > it does mean you don't have to write and insmod modules.  The real power
> > is that you can *dynamically* switch between the hard/soft real-time
> > modes from within your application.  Of course while in soft mode, you
> > can make normal Linux system calls etc.


Download version 1.2 from http://www.rtai.org/ and look in the lxrt
sub-directory.  Basically, RTAI has its own set of syscalls, to move a
process into the hard realtime mode, it make a syscall that sets the
process in a state whereby linux no longer schedules it, and RTAI takes
over scheduling responsibility.  To use this mode, a user has to lock
his pages into memory with mlock.  You are correct that RTAI system does
switch the mmu context.

Regards, Stuart