I had a similar problem and solved it as follows:
It was impossible to trigger a user-task from an rt-task, but it can be done
from a normal (non-rt) Linux kernel module.
The way I did it was to create a bunch of read-only "devices", one each for
100 Hz, 50 Hz, 25 Hz, etc (but you can subdivide the x86 100 Hz jiffy (of
the Alpha's 1 kHz) any way you want.
To execute periodically, a user-task opens and reads from one of these
devices. The read-operation blocks until the next time the associated clock
strikes at which time all tasks that were blocked reading that "device" are
released. (The normal Linux kernel functions sleep_on_interruptible() and
wake_up_interruptible() are perfect for this magic.) The actual "data"
returned from the read are irrelevant, the only thing that's significant is
that the read-operation completes at the rate associated with the device.
Norm Dresner
Fellow Systems Engineer
Radar Systems Engineering Department
Electronic Systems and Sensors Segment
Northrop Grumman Corporation
MS 520
Box 746
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> -----Original Message-----
> From: Troy Davis [SMTP:[EMAIL PROTECTED]]
> Sent: Thursday, August 24, 2000 12:28 PM
> To: [EMAIL PROTECTED]
> Subject: [rtl] thread scheduling in user space
>
> Hello all-
> I want to create a thread (or process) that executes on a regular
> basis (about 20 times per second - 20 hz) in user space. Doing this
> using the rtlinux thread library in kernel space is very easy, but it
> does not appear to be the case in user space using the regular pthread
> library in linux. Another method of doing this would be to utilize a
> rtlinux timer or thread in a module but I'm unsure of how to trigger a
> function in user space from an event in rtlinux. What I'm trying to do
> is create an interrupt driven read/write function in user space to send
> and poll for messages over a tcp/ip connection. The messages being sent
> over tcp/ip do not need to occur in real-time, so a simple 'is there a
> message? okay - send it or receive it' will work. Anyone have any
> ideas on this?
>
> Troy Davis
> Airborne Data Systems, Inc.
>
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