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| -rw-r--r-- | Documentation/rtc.txt | 44 |
1 files changed, 23 insertions, 21 deletions
diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt index ddc366026e00..47feb4414b7e 100644 --- a/Documentation/rtc.txt +++ b/Documentation/rtc.txt @@ -1,6 +1,6 @@ - - Real Time Clock (RTC) Drivers for Linux - ======================================= +======================================= +Real Time Clock (RTC) Drivers for Linux +======================================= When Linux developers talk about a "Real Time Clock", they usually mean something that tracks wall clock time and is battery backed so that it @@ -32,8 +32,8 @@ only issue an alarm up to 24 hours in the future, other hardware may be able to schedule one any time in the upcoming century. - Old PC/AT-Compatible driver: /dev/rtc - -------------------------------------- +Old PC/AT-Compatible driver: /dev/rtc +-------------------------------------- All PCs (even Alpha machines) have a Real Time Clock built into them. Usually they are built into the chipset of the computer, but some may @@ -105,8 +105,8 @@ that will be using this driver. See the code at the end of this document. (The original /dev/rtc driver was written by Paul Gortmaker.) - New portable "RTC Class" drivers: /dev/rtcN - -------------------------------------------- +New portable "RTC Class" drivers: /dev/rtcN +-------------------------------------------- Because Linux supports many non-ACPI and non-PC platforms, some of which have more than one RTC style clock, it needed a more portable solution @@ -136,35 +136,37 @@ 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 +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 +================ ============================================================== +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 +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 +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. + 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. +================ ============================================================== -IOCTL INTERFACE +IOCTL interface --------------- The ioctl() calls supported by /dev/rtc are also supported by the RTC class |