From: Sascha Hauer <s.hauer@pengutronix.de>
To: "Jan Lübbe" <jlu@pengutronix.de>
Cc: barebox@lists.infradead.org, Daniel Schultz <d.schultz@phytec.de>
Subject: Re: [PATCH v3 2/2] ARM: am335x: Changed timer
Date: Mon, 20 Jul 2015 07:36:05 +0200 [thread overview]
Message-ID: <20150720053605.GT18700@pengutronix.de> (raw)
In-Reply-To: <1437145068.3498.117.camel@pengutronix.de>
On Fri, Jul 17, 2015 at 04:57:48PM +0200, Jan Lübbe wrote:
> On Fr, 2015-07-17 at 15:39 +0200, Daniel Schultz wrote:
> > The dmtimer0 is too inaccurate to be used for measurements.
> > We switch to the more accurate dmtimer2.
>
> Ah, OK, after looking at the TRM again, the real reason for the
> inaccuracy seems to be that the 32KiHz for dmtimer0 is *not* derived
> from the RTC crystal, but from an internal RC oscillator.
>
> The kernel uses dmtimer1 for the clocksource by switching it to the
> M_OSC in the PRCM.
>
> The dmtimer2 is used for clockevents and runs from M_OSC by default.
> While we could set the dmtimer1 source to M_OSC in the clock setup, it
> seems simpler to just use dmtimer2.
>
> The commit message should explain the reasoning behind the switch.
Changed the commit message while applying to:
The 32KHz from dmtimer0 is derived from a SoC internal RC oscillator
which is quite inaccurate. Switch to dmtimer2 which is driven from
the high frequency oscillator clock.
Sascha
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prev parent reply other threads:[~2015-07-20 5:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-17 13:39 Daniel Schultz
2015-07-17 14:57 ` Jan Lübbe
2015-07-20 5:36 ` Sascha Hauer [this message]
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