Re: [Xenomai-help] gpioirqbench: measuring external interrupt latencies

[Wolfgang Grandegger <wg@domain.hid>]

Jan Kiszka wrote:
> Wolfgang Grandegger wrote:
>> Hello,
>>
>> I'm proud to announce "gpioirqbench", a benchmark tool to measure
>> external interrupt latencies. It is derived from Jan's irqbench [1] for
>> the PC. Instead of using the serial or parallel port, it uses GPIO pins
>> on embedded systems. It measures the time between the generation of an
>> interrupt triggered by a GPIO pin and the reply by either the interrupt
>> service routine, a kernel-space task or a user-space task. As reply,
>> another GPIO pin will be toggled. The setup consists of two systems, the
>> log host and the test target. The log host triggers the interrupt on the
>> test target and measures the latency. This benchmark is primarily for
>> Xenomai/RTDM, but it can also be used for plain Linux or even Linux-rt
>> (with the real-time preemption patch).
> 
> Nice stuff! Still I have a few conceptual questions: :->

I did expect them ;-).

> 1. Why do you need a Xenomai measurement host? On first glance, you are
>    just spinning on the reply for the RT target. Why not use plain Linux
>    for this to increase portability? Most beautiful would be a pure
>    userspace approach like for irqbench. What prevents this here?

Well, I'm not a hardware expert and therefore it was not obvious to me
how to connect GPIO pins to the standard PC. To avoid electrical
incompatibilities, I chose my good old TQM855L module as log host.
I agree, that this solution is rather special and that the one for
irqbench would be much better. Any ideas how to interface GPIO pins with
the PC?

> 2. Do you see a chance to integrate the target'S GPIO interface into the
>    exiting irqbench backend? That would make it easy to merge the
>    Xenomai version into the tree.

In the end I preferred to make a separated distribution, as various
parts are very hardware specific and the driver can also be built as
normal Linux character device driver.

Wolfgang.