Biju!
On Wed, Dec 07 2022 at 11:35, Biju Das wrote:
>> Subject: RE: [PATCH 0/6] Add RZ/V2M Compare-Match Timer (TIM) support
>> On Wed, Dec 07 2022 at 07:52, Biju Das wrote:
>> > Basically, this HW timer is used for measuring the processing time of
>> > DRP-AI accurately compared to the CPU timer normally we use.
>>
>> How is a slow to access timer with a lower clock frequency more accurate?
>
> But our tick frequency for arm64 defconfig is CONFIG_HZ_250=y. So we
> get timer interrupt at every 4 msec.
CONFIG_HIGH_RES_TIMERS=y
> How do we get timer event interrupt, eg: for 1 microsec?
clock_nanosleep(...);
Though 1usec is wishful thinking with either variant of timer hardware.
>>
>> We are debating a clocksource/clockevent driver and not a counter driver,
>> right?
>
> Yes, Rob pointed out we should not misuse the compatibles as I have both
> Timer and counter bindings for a given HW timer.
>
> Timer, It can be used as broadcast and highres timer for RT.
I buy the broadcast part if you really have a ARM architected timer
which stops in deep idle states. Highres for RT, no! The arm architected
timer works perfectly fine for that.
> Counter, It can be used as measuring the processing time of DRP-AI.
Sigh. You can do that with the architected timer too, especially when
you are going to do the measurement in user space.
clock_gettime(), which uses the VDSO with the architected timer is fast
to access and accurate.
Thanks,
tglx
