| 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 upto 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. |