Re: EVL Interrupt

[Philippe Gerum <rpm@xenomai.org>]

Sebastian Blaesing via Xenomai <xenomai@xenomai.org> writes:

> Hi all,
>
> what is the best and fastest way to pass critical hardware Irq signal
> to control a semaphore in user space application?
>
> Is it possible that kernel and user space share a semaphore?
>

You do this indirectly: in the kernel driver which implements the IRQ
handler, you create an EVL sema4, and an oob_ioctl() or oob_read()
handler which waits on it. The IRQ handler posts the sema4 which the
user-space application pends on via a call to oob_{ioctl|read}().

The driver which talks to the 'latmus' application implements the same
pattern, using an EVL flag instead of a sema4, but the logic is
otherwise the same. Some handler triggered by some event (here a timer,
yours would be triggered by an IRQ) raises a flag [1], which is awaited
by a function [2] which is called by the application via the oob_ioctl()
syscall [3].

HTH,

[1] https://source.denx.de/Xenomai/xenomai4/linux-evl/-/blob/v5.15.y-evl-rebase/drivers/evl/latmus.c#L561
[2] https://source.denx.de/Xenomai/xenomai4/linux-evl/-/blob/v5.15.y-evl-rebase/drivers/evl/latmus.c#L627
[3]
https://source.denx.de/Xenomai/xenomai4/linux-evl/-/blob/v5.15.y-evl-rebase/drivers/evl/latmus.c#L1130

--
Philippe.