base-linux IRQ session

[Johannes Kliemann]

Hello Christian,

thanks for that hint, it was the missing piece. I can now happily
announce that Interrupts are working on Genode with base-linux!

Regards,
Johannes

Am 13.03.2018 um 16:25 schrieb Christian Helmuth:
> Hello Johannes,
> 
> On Tue, Mar 13, 2018 at 01:36:09PM +0100, Johannes Kliemann wrote:
>> I'm currently implementing the IRQ session on base-linux.
>> If I understood the Foundations book correctly interrupts are waiting in
>> a separate thread that locks when it is waiting and continues (and calls
>> the handler) once an interrupt is triggered.
> 
> The core-internal implementation depends on the base platform. On NOVA
> and FOC, the Irq_object (which is a thread) is never started, ie.,
> does not execute an entry function. Other platforms (e.g., OKL4) use
> the Irq_object thread to implement a interrupt-wait-and-signal loop.
> 
>> According to this I have implemented a kernel module [1] that triggers
>> interrupts via reads on a device file. The interrupt can be registered
>> via ioctl on the file descriptor and the a blocking read is called that
>> returns once the registered interrupts has been triggered.
>>
>> I have looked into the implementations of base-nova and base-hw but
>> didn't completely understand it. As far as I understood the session
>> component implements the session and only requires the interrupt number
>> and a signal handler.
>> The Irq_object implements the waiting thread but I didn't see where it
>> is waiting for the interrupt.
>> Also as far as I could see it the actual interrupt capability stays
>> inside the session in core and only the signal handler capability is
>> passed to the component.
> 
> I suggest you refer to OKL4
> 
>   base-okl4/src/core/irq_session_component.cc
> 
> and implement an Irq_object working similarly with a entry() function
> that uses Irq_object::_wait_for_irq() (which blocks in read(dev_fd))
> and signals IRQ occurence by Genode::Signal_transmitter(_sig_cap).submit(1)
> 
>> Is my understanding of this correct? And is there any further
>> documentation on this?
> 
> Unfortunately, there's only few documentation of the core internals.
> To get up-to-date information I suggest looking at the code and asking
> here or even on Freenode
> 
>   http://webchat.freenode.net/?randomnick=1&channels=%23genode&uio=d4
> 
> Regards
>