Jan Kiszka wrote:
On 2011-06-05 10:46, Armin Steinhoff wrote:
Nicholas Mc Guire wrote:
On Sat, 04 Jun 2011, Monica Puig-Pey wrote:
Hello,
I'm studying how to develop drivers in a real time OS and how do they
work. I'm using Ubuntu 10.04 with the 2.6.31-11-rt patch installed.
I would like to know the priority when executing open(), read(), write()
and close() operations.
In my example the thread which is using the driver runs with 10 RTPRIO,
but I don't know what happens in kernel context with the priority when
running the I/O operations.
Thank you for your help, I don't know where to learn about this.
[]
Also when using bottom half mechanisms you need to take into account the
priority of the kernel thread that manages the defered work items, so
rt-drivers may have a different structure than normal drivers.
That's the reason why I prefer UIO based user space drivers !
...which are forced to use threaded IRQs over -rt as well.
What's wrong with that approach? You have an ISR in the kernel module
and an interrupt thread at user space.
Seem OK for me since a long time with QNX :)
Taking threaded IRQs out of the picture, bottom-half mechanisms usually
come into play when dispatch workload that cannot be assigned to a
specific user context is significant. But then UIO is the wrong approach
anyway as it doesn't match well the requirements of multi-user device
interfaces.
Support of multi-user device interfaces at user space is just a
design issue ... I use this concept since a long time with QNX :)
--Armin
Jan
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