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Diffstat (limited to 'Documentation/rtc.txt')
| -rw-r--r-- | Documentation/rtc.txt | 81 |
1 files changed, 2 insertions, 79 deletions
diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt index c0c977445fb9..a129acf38537 100644 --- a/Documentation/rtc.txt +++ b/Documentation/rtc.txt @@ -136,82 +136,5 @@ a high functionality RTC is integrated into the SOC. That system might read the system clock from the discrete RTC, but use the integrated one for all other tasks, because of its greater functionality. -SYSFS interface ---------------- - -The sysfs interface under /sys/class/rtc/rtcN provides access to various -rtc attributes without requiring the use of ioctls. All dates and times -are in the RTC's timezone, rather than in system time. - -================ ============================================================== -date RTC-provided date -hctosys 1 if the RTC provided the system time at boot via the - CONFIG_RTC_HCTOSYS kernel option, 0 otherwise -max_user_freq The maximum interrupt rate an unprivileged user may request - from this RTC. -name The name of the RTC corresponding to this sysfs directory -since_epoch The number of seconds since the epoch according to the RTC -time RTC-provided time -wakealarm The time at which the clock will generate a system wakeup - event. This is a one shot wakeup event, so must be reset - after wake if a daily wakeup is required. Format is seconds - since the epoch by default, or if there's a leading +, seconds - in the future, or if there is a leading +=, seconds ahead of - the current alarm. -offset The amount which the rtc clock has been adjusted in firmware. - Visible only if the driver supports clock offset adjustment. - The unit is parts per billion, i.e. The number of clock ticks - which are added to or removed from the rtc's base clock per - billion ticks. A positive value makes a day pass more slowly, - longer, and a negative value makes a day pass more quickly. -*/nvmem The non volatile storage exported as a raw file, as described - in Documentation/nvmem/nvmem.txt -================ ============================================================== - -IOCTL interface ---------------- - -The ioctl() calls supported by /dev/rtc are also supported by the 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. - - * RTC_RD_TIME, RTC_SET_TIME ... every RTC supports at least reading - time, returning the result as a Gregorian calendar date and 24 hour - wall clock time. To be most useful, this time may also be updated. - - * RTC_AIE_ON, RTC_AIE_OFF, RTC_ALM_SET, RTC_ALM_READ ... when the RTC - is connected to an IRQ line, it can often issue an alarm IRQ up to - 24 hours in the future. (Use RTC_WKALM_* by preference.) - - * RTC_WKALM_SET, RTC_WKALM_RD ... RTCs that can issue alarms beyond - the next 24 hours use a slightly more powerful API, which supports - setting the longer alarm time and enabling its IRQ using a single - request (using the same model as EFI firmware). - - * RTC_UIE_ON, RTC_UIE_OFF ... if the RTC offers IRQs, the RTC framework - will emulate this mechanism. - - * RTC_PIE_ON, RTC_PIE_OFF, RTC_IRQP_SET, RTC_IRQP_READ ... these icotls - are emulated via a kernel hrtimer. - -In many cases, the RTC alarm can be a system wake event, used to force -Linux out of a low power sleep state (or hibernation) back to a fully -operational state. For example, a system could enter a deep power saving -state until it's time to execute some scheduled tasks. - -Note that many of these ioctls are handled by the common rtc-dev interface. -Some common examples: - - * RTC_RD_TIME, RTC_SET_TIME: the read_time/set_time functions will be - called with appropriate values. - - * RTC_ALM_SET, RTC_ALM_READ, RTC_WKALM_SET, RTC_WKALM_RD: gets or sets - the alarm rtc_timer. May call the set_alarm driver function. - - * RTC_IRQP_SET, RTC_IRQP_READ: These are emulated by the generic code. - - * RTC_PIE_ON, RTC_PIE_OFF: These are also emulated by the generic code. - -If all else fails, check out the tools/testing/selftests/timers/rtctest.c test! +Check out tools/testing/selftests/timers/rtctest.c for an example usage of the +ioctl interface. |