What:		/dev/rtcX
Date:		April 2005
KernelVersion:	2.6.12
Contact:	linux-rtc@vger.kernel.org
Description:
		The ioctl interface to drivers for real-time clocks (RTCs).
		Following actions are supported:

		* RTC_RD_TIME, RTC_SET_TIME: Read or set the RTC time. Time
		  format is a Gregorian calendar date and 24 hour wall clock
		  time.

		* RTC_AIE_ON, RTC_AIE_OFF: Enable or disable the alarm interrupt
		  for RTCs that support alarms

		* RTC_ALM_READ, RTC_ALM_SET: Read or set the alarm time for
		  RTCs that support alarms. Can be set up to 24 hours in the
		  future. Requires a separate RTC_AIE_ON call to enable the
		  alarm interrupt. (Prefer to use RTC_WKALM_*)

		* RTC_WKALM_RD, RTC_WKALM_SET: For RTCs that support a more
		  powerful interface, which can issue alarms beyond 24 hours and
		  enable IRQs in the same request.

		* RTC_PIE_ON, RTC_PIE_OFF: Enable or disable the periodic
		  interrupt for RTCs that support periodic interrupts.

		* RTC_UIE_ON, RTC_UIE_OFF: Enable or disable the update
		  interrupt for RTCs that support it.

		* RTC_IRQP_READ, RTC_IRQP_SET: Read or set the frequency for
		  periodic interrupts for RTCs that support periodic interrupts.
		  Requires a separate RTC_PIE_ON call to enable the periodic
		  interrupts.

		* RTC_VL_READ: Read the voltage inputs status of the RTC when
		  supported. The value is a bit field of RTC_VL_*, giving the
		  status of the main and backup voltages.

		* RTC_VL_CLEAR: Clear the voltage status of the RTC. Some RTCs
		  need user interaction when the backup power provider is
		  replaced or charged to be able to clear the status.

		The ioctl() calls supported by the older /dev/rtc interface are
		also supported by the newer RTC class framework. However,
		because the chips and systems are not standardized, some PC/AT
		functionality might not be provided. And in the same way, some
		newer features -- including those enabled by ACPI -- are exposed
		by the RTC class framework, but can't be supported by the older
		driver.