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The rtc's status register allows to determine if a 32k crystal is connected to keep the rtc running in low power states provided the corresponding fuse bits were blown correctly during production. (In case they were not, the right frequency can be stated in the device tree.) If there is no such crystal available force the 24 MHz XTAL clock to keep running to retain the right date and time. Otherwise use the crystal to save some power. It would be nice to only switch to the crystal when the XTAL clock is about to be disabled and keep the crystal off when unneeded because XTAL is always on while the chip is powered on. But as sudden power loss isn't detectable this is not save. Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Cc: Alessandro Zummo <a.zummo@towertech.it> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
22 lines
565 B
Plaintext
22 lines
565 B
Plaintext
* STMP3xxx/i.MX28 Time Clock controller
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Required properties:
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- compatible: should be one of the following.
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* "fsl,stmp3xxx-rtc"
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- reg: physical base address of the controller and length of memory mapped
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region.
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- interrupts: rtc alarm interrupt
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Optional properties:
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- stmp,crystal-freq: override crystal frequency as determined from fuse bits.
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Only <32000> and <32768> are possible for the hardware. Use <0> for
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"no crystal".
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Example:
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rtc@80056000 {
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compatible = "fsl,imx28-rtc", "fsl,stmp3xxx-rtc";
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reg = <0x80056000 2000>;
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interrupts = <29>;
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};
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