1 What:		/dev/rtcX
2 Date:		April 2005
3 KernelVersion:	2.6.12
4 Contact:	linux-rtc@vger.kernel.org
5 Description:
6 		The ioctl interface to drivers for real-time clocks (RTCs).
7 		Following actions are supported:
8 
9 		* RTC_RD_TIME, RTC_SET_TIME: Read or set the RTC time. Time
10 		  format is a Gregorian calendar date and 24 hour wall clock
11 		  time.
12 
13 		* RTC_AIE_ON, RTC_AIE_OFF: Enable or disable the alarm interrupt
14 		  for RTCs that support alarms
15 
16 		* RTC_ALM_READ, RTC_ALM_SET: Read or set the alarm time for
17 		  RTCs that support alarms. Can be set upto 24 hours in the
18 		  future. Requires a separate RTC_AIE_ON call to enable the
19 		  alarm interrupt. (Prefer to use RTC_WKALM_*)
20 
21 		* RTC_WKALM_RD, RTC_WKALM_SET: For RTCs that support a more
22 		  powerful interface, which can issue alarms beyond 24 hours and
23 		  enable IRQs in the same request.
24 
25 		* RTC_PIE_ON, RTC_PIE_OFF: Enable or disable the periodic
26 		  interrupt for RTCs that support periodic interrupts.
27 
28 		* RTC_UIE_ON, RTC_UIE_OFF: Enable or disable the update
29 		  interrupt for RTCs that support it.
30 
31 		* RTC_IRQP_READ, RTC_IRQP_SET: Read or set the frequency for
32 		  periodic interrupts for RTCs that support periodic interrupts.
33 		  Requires a separate RTC_PIE_ON call to enable the periodic
34 		  interrupts.
35 
36 		* RTC_VL_READ: Read the voltage inputs status of the RTC when
37 		  supported. The value is a bit field of RTC_VL_*, giving the
38 		  status of the main and backup voltages.
39 
40 		* RTC_VL_CLEAR: Clear the voltage status of the RTC. Some RTCs
41 		  need user interaction when the backup power provider is
42 		  replaced or charged to be able to clear the status.
43 
44 		The ioctl() calls supported by the older /dev/rtc interface are
45 		also supported by the newer RTC class framework. However,
46 		because the chips and systems are not standardized, some PC/AT
47 		functionality might not be provided. And in the same way, some
48 		newer features -- including those enabled by ACPI -- are exposed
49 		by the RTC class framework, but can't be supported by the older
50 		driver.
51