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SubjectRe: getting timestamp of last interrupt?
On Mon, 6 Oct 2003, Hans-Georg Thien wrote:

> Richard B. Johnson wrote:
> > On Sat, 4 Oct 2003, Hans-Georg Thien wrote:
> >
> >
> >>> [...]
> >>>>I am looking for a possibility to read out the last timestamp when an
> >>>>interrupt has occured.
> >>>>
> >>>>e.g.: the user presses a key on the keyboard. Where can I read out the
> >>>>timestamp of this event?
> >>>
> >>>
> >>>You can get A SIGIO signal for every keyboard, (or other input) event.
> >>>What you do with it is entirely up to you. Linux/Unix doesn't have
> >>>"callbacks", instead it has signals. It also has select() and poll(),
> >>>all useful for handling such events. If you want a time-stamp, you
> >>>call gettimeofday() in your signal handler.
> >>>
> >>
> >>Thanks a lot Richard,
> >>
> >>... but ... can I use signals in kernel mode?
> >
> >
> > Well you talked about the user pressing a key and getting
> > a time-stamp as a result. If you need time-stamps
> > inside the kernel, i.e, a module, then you can call
> > the kernel's do_gettimeofday() function.
> >
> Hello Richard, - It seems, that I should be more precise about what I
> exactly mean...
>
>
> I'm writing a kernel mode device driver (mouse).
>
> In that device driver I need the timestamp of the last event for another
> kernel mode device (keyboard).
>
> I do not care if that timestamp is in jiffies or in gettimeofday()
> format or whatever format does exist in the world. I am absolutely sure
> I can convert it somehow to fit my needs.
>
> But since it is a kernel mode driver it can not -AFAIK- use the signal()
> syscall.
>
> -Hans

Then it gets real simple. Just use jiffies, if you can stand the
wrap that will occur every (2^32 -1)/HZ seconds ~= 497 days with
HZ = 100. If not, call sys_gettimeofday(). Also, if your events
are closer in time than a HZ, then you must get time from
sys_gettimeofday().

Cheers,
Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips).
Note 96.31% of all statistics are fiction.


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