[i2c] Question on ds1339's oscillator

[Rodolfo Giometti]

On Fri, Jun 15, 2007 at 08:19:50AM -0700, David Brownell wrote:
> 
> Glad to hear it ... do you have the latest patches?
> 
>   http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.22-rc4
> 	/2.6.22-rc4-mm2/broken-out/rtc-ds1307-cleanups.patch
> 
> plus the appended patch, converting to a new style driver so that
> the alarm IRQ is in hand.  As noted, the rtc-rs5c372 driver has
> partial support (alarm IRQ not hooked up!) for alarms

Yes, I already applied such patches.

> Say what --- an RTC can function with its oscillator off??
> 
> Or are you saying that check is incorrect?  I could imagine
> that OSFt should maybe be ignored, other than for purposes
> of issuing a warning (before clearing it).

My board has a micro controller that, at boot, disables such
oscillator in order to avoid the square wave form at the output pin. When
the driver starts up it recognizes that the oscillator is off and exits... but since
old version worked well I simplyremoved the

	goto exit_free;

line and the RTC continue to work properly.

To be honest I still doesn't well understand what the oscillator is
used for... :-/ In the past I supposed that it was needed turned on
but in reality this is not true. Now I suppose it is useful only to
generate the square wave form.

> Yes, certainly.  The general policy should be, I think, that the
> RTC init sequence won't change configuration ... so that for example
> if you're given system with the square wave output already set up,
> the assumption should be that the board is wired to require that.

Mmm... that is true if you have an external micro controller that
configures the RTC for your otherwise how can the CPU setup the
initial configuration if the driver is not yet renning? :-o

I think that we should force IRQ output if the board configuration
define an irq line otherwise we can the square wave form as outout.

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti at enneenne.com
Linux Device Driver                             giometti at gnudd.com
Embedded Systems                     		giometti at linux.it
UNIX programming                     phone:     +39 349 2432127
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