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Clock and Hardware Timer usage
- Date: Thu, 3 Jul 2003 04:01:34 -0700 (PDT)
- From: cedric_aubert at yahoo.fr (Cedric Aubert)
- Subject: Clock and Hardware Timer usage
> -----Original Message-----
> From: Victor V. Vengerov [mailto:vvv at oktet.ru]
> Sent: Thursday, July 03, 2003 12:27 PM
> To: cedric_aubert at yahoo.fr
> Cc: RTEMS-USERS; Joel Sherrill
> Subject: Re: Clock and Hardware Timer usage
> Cedric Aubert wrote:
> >To me, hardware need to RTEMS for all software kind
> >use :
> >- one varying HW interval timer
> >- one RTC
> >That all.
> I have missed part of discussion, but I'll add my 2
> Consider following:
> - not every hardware has RTC, although it may keep
> (think about CD/cassete player which is running in
> mode when turned off and handle timer interrupts
It's not a problem, still not use RTC and simple use
HW timer at 1 sec frequency interruption like we are
with joel. :-)
It's mandatory to have always some timer IT, to known
and for still have timeslice tasking. In fact if no
timeout is need
by the software user, you will have the period clock
as today concept.
But if some user application need timeout, you will
have always the
period clock IT but also the user timeout IT on the
same HW Timer.
> - Frequently, RTC chip has so simple interface that
it is hard to
> use from software efficiently. There are many
> which are I2C/SPI accessible. Access to them is
> 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
Not a problem to, read the RTC only at boot time and
still keep alive
current TOD with the same at least 1 second interrupt
from the varying
> So, even if your concept is correct, it may be hard
to apply it
> to the current state of technology.
I don't think so. I have today a proprietary RTOS who
this same concept.
It's difficult to understand this concept of one only
I have talk about this with many compagny like OSE,
VxWorks,... no one
understand very well that, and of course don't have
RTOS are very very often base with a fixed time of
Some one have a second timer and implement a part of
But this concept is more performant.
The advantage of this concept, it's to have precision
deterioration. And still have time slice and other
> Please, sorry if my comment do not fit into context
> discussion: I have not read/understand it
> Victor V. Vengerov
> OKTET Ltd.
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