[i2c] Question on ds1339's oscillator

[Rodolfo Giometti]

On Fri, Jun 15, 2007 at 09:24:33AM -0700, David Brownell wrote:
> 
> Erm, not at all.  The oscillator is what drives the RTC
> clock ... you know, the tick/tock/tick/tock/... part.
> RTCs just count oscillator cycles.  If no oscillator is
> running, the reported time will never change.
> 
> The square wave output is a different thing entirely.
> Oscillator output may optionally be sent out on one pin
> of many RTCs (probably divided down) ... maybe the board
> needs a 32 kiHz signal to drive another circuit.

If so, why does my RTC work even if the bit EOSC is off?

> The boot loader can do it, but more likely that was done as part
> of manufacturing the board ... along with initializing the clock
> used by the RTC.

Mmm...

> > 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.
> 
> And when the Linux configuration was a mistake, and then the
> circuit which needed that clock stops working correctly ...?
> 
> If the board setup provides an IRQ and the chip is configured
> to generate square wave output, that's clearly a bug somewhere.
> 
> Issuing a warning is clearly appropriate.  Reconfiguring the
> hardware, on the assumption that the Linux config is right,
> seems dangerous to me.  That's not a good way to fix bugs in
> the production line (including the bootloader).

I don't agree.

1) If you are the kernel programmer you MUST to know what you are
doing, so if you select the IRQ line this means that your board MUST
use the IRQ line and NOT the square wave.

2) The boot loader should init the board JUST for the boot, then the
kernel should configure the whole system for proper use.

In any case the kernel must have the last word in system setup.

This is the u-boot way. :)

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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