Clock and Hardware Timer usage

Joel Sherrill joel.sherrill at
Thu Jul 3 13:58:49 UTC 2003

"Victor V. Vengerov" wrote:
> Cederic,
> Cedric Aubert wrote:
> >
> >To me, hardware need to RTEMS for all software kind of
> >use :
> >
> >- one varying HW interval timer
> >- one RTC
> >
> >That all.
> >
> I have missed part of discussion, but I'll add my 2 kopeyki.
> Consider following:
> - not every hardware has RTC, although it may keep clock
>   (think about CD/cassete player which is running in low-power
>    mode when turned off and handle timer interrupts to keep
>    clock)
> - Frequently, RTC chip has so simple interface that it is hard to
>   use from software efficiently. There are   many RTC chips
>   which are I2C/SPI accessible. Access to them is slow enough
>   to perform it in everyday operations. I beleive, even access to
>   PC clock may be slow enough: although it has simple I/O port
>   interface, actual delays may be hidden in hardware.
> So, even if your concept is correct, it may be hard to apply it
> to the current state of technology.
> Please, sorry if my comment do not fit into context of this
> discussion: I have not read/understand it completely.

I agree with both those statements.  I really believe there is
more potential benefit with the capability to use a variable
interval timer.

Of course, I haven't considered that there is currently a way
to obtain "ticks since boot" through the API.  If you don't get a
clock tick at a regular period, then this won't get incremented
correctly.  This could break programs... :(

> Victor
> --
> Victor V. Vengerov
> OKTET Ltd.
> Ulianovskaya st., 1, office 533, St.-Petersburg 198504 Russia
> phone: +7 812 4284384(work),+7 812 9389372(mobile),+7 812 4281653(home)

Joel Sherrill, Ph.D.             Director of Research & Development
joel at                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
Support Available                (256) 722-9985

More information about the users mailing list