0001 What: /dev/rtcX
0002 Date: April 2005
0003 KernelVersion: 2.6.12
0004 Contact: linux-rtc@vger.kernel.org
0005 Description:
0006 The ioctl interface to drivers for real-time clocks (RTCs).
0007 Following actions are supported:
0008
0009 * RTC_RD_TIME, RTC_SET_TIME: Read or set the RTC time. Time
0010 format is a Gregorian calendar date and 24 hour wall clock
0011 time.
0012
0013 * RTC_AIE_ON, RTC_AIE_OFF: Enable or disable the alarm interrupt
0014 for RTCs that support alarms
0015
0016 * RTC_ALM_READ, RTC_ALM_SET: Read or set the alarm time for
0017 RTCs that support alarms. Can be set upto 24 hours in the
0018 future. Requires a separate RTC_AIE_ON call to enable the
0019 alarm interrupt. (Prefer to use RTC_WKALM_*)
0020
0021 * RTC_WKALM_RD, RTC_WKALM_SET: For RTCs that support a more
0022 powerful interface, which can issue alarms beyond 24 hours and
0023 enable IRQs in the same request.
0024
0025 * RTC_PIE_ON, RTC_PIE_OFF: Enable or disable the periodic
0026 interrupt for RTCs that support periodic interrupts.
0027
0028 * RTC_UIE_ON, RTC_UIE_OFF: Enable or disable the update
0029 interrupt for RTCs that support it.
0030
0031 * RTC_IRQP_READ, RTC_IRQP_SET: Read or set the frequency for
0032 periodic interrupts for RTCs that support periodic interrupts.
0033 Requires a separate RTC_PIE_ON call to enable the periodic
0034 interrupts.
0035
0036 * RTC_VL_READ: Read the voltage inputs status of the RTC when
0037 supported. The value is a bit field of RTC_VL_*, giving the
0038 status of the main and backup voltages.
0039
0040 * RTC_VL_CLEAR: Clear the voltage status of the RTC. Some RTCs
0041 need user interaction when the backup power provider is
0042 replaced or charged to be able to clear the status.
0043
0044 The ioctl() calls supported by the older /dev/rtc interface are
0045 also supported by the newer RTC class framework. However,
0046 because the chips and systems are not standardized, some PC/AT
0047 functionality might not be provided. And in the same way, some
0048 newer features -- including those enabled by ACPI -- are exposed
0049 by the RTC class framework, but can't be supported by the older
0050 driver.
