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1What: /dev/rtcX2Date: April 20053KernelVersion: 2.6.124Contact: linux-rtc@vger.kernel.org5Description: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. Time10 format is a Gregorian calendar date and 24 hour wall clock11 time.12 13 * RTC_AIE_ON, RTC_AIE_OFF: Enable or disable the alarm interrupt14 for RTCs that support alarms15 16 * RTC_ALM_READ, RTC_ALM_SET: Read or set the alarm time for17 RTCs that support alarms. Can be set upto 24 hours in the18 future. Requires a separate RTC_AIE_ON call to enable the19 alarm interrupt. (Prefer to use RTC_WKALM_*)20 21 * RTC_WKALM_RD, RTC_WKALM_SET: For RTCs that support a more22 powerful interface, which can issue alarms beyond 24 hours and23 enable IRQs in the same request.24 25 * RTC_PIE_ON, RTC_PIE_OFF: Enable or disable the periodic26 interrupt for RTCs that support periodic interrupts.27 28 * RTC_UIE_ON, RTC_UIE_OFF: Enable or disable the update29 interrupt for RTCs that support it.30 31 * RTC_IRQP_READ, RTC_IRQP_SET: Read or set the frequency for32 periodic interrupts for RTCs that support periodic interrupts.33 Requires a separate RTC_PIE_ON call to enable the periodic34 interrupts.35 36 * RTC_VL_READ: Read the voltage inputs status of the RTC when37 supported. The value is a bit field of RTC_VL_*, giving the38 status of the main and backup voltages.39 40 * RTC_VL_CLEAR: Clear the voltage status of the RTC. Some RTCs41 need user interaction when the backup power provider is42 replaced or charged to be able to clear the status.43 44 The ioctl() calls supported by the older /dev/rtc interface are45 also supported by the newer RTC class framework. However,46 because the chips and systems are not standardized, some PC/AT47 functionality might not be provided. And in the same way, some48 newer features -- including those enabled by ACPI -- are exposed49 by the RTC class framework, but can't be supported by the older50 driver.51