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@@ -1,6 +1,6 @@
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-
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- Real Time Clock (RTC) Drivers for Linux
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- =======================================
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+=======================================
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+Real Time Clock (RTC) Drivers for Linux
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+=======================================
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When Linux developers talk about a "Real Time Clock", they usually mean
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something that tracks wall clock time and is battery backed so that it
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@@ -32,8 +32,8 @@ only issue an alarm up to 24 hours in the future, other hardware may
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be able to schedule one any time in the upcoming century.
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- Old PC/AT-Compatible driver: /dev/rtc
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- --------------------------------------
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+Old PC/AT-Compatible driver: /dev/rtc
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+--------------------------------------
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All PCs (even Alpha machines) have a Real Time Clock built into them.
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Usually they are built into the chipset of the computer, but some may
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@@ -105,8 +105,8 @@ that will be using this driver. See the code at the end of this document.
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(The original /dev/rtc driver was written by Paul Gortmaker.)
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- New portable "RTC Class" drivers: /dev/rtcN
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- --------------------------------------------
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+New portable "RTC Class" drivers: /dev/rtcN
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+--------------------------------------------
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Because Linux supports many non-ACPI and non-PC platforms, some of which
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have more than one RTC style clock, it needed a more portable solution
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@@ -136,35 +136,37 @@ a high functionality RTC is integrated into the SOC. That system might read
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the system clock from the discrete RTC, but use the integrated one for all
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other tasks, because of its greater functionality.
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-SYSFS INTERFACE
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+SYSFS interface
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---------------
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The sysfs interface under /sys/class/rtc/rtcN provides access to various
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rtc attributes without requiring the use of ioctls. All dates and times
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are in the RTC's timezone, rather than in system time.
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-date: RTC-provided date
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-hctosys: 1 if the RTC provided the system time at boot via the
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+================ ==============================================================
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+date RTC-provided date
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+hctosys 1 if the RTC provided the system time at boot via the
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CONFIG_RTC_HCTOSYS kernel option, 0 otherwise
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-max_user_freq: The maximum interrupt rate an unprivileged user may request
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+max_user_freq The maximum interrupt rate an unprivileged user may request
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from this RTC.
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-name: The name of the RTC corresponding to this sysfs directory
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-since_epoch: The number of seconds since the epoch according to the RTC
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-time: RTC-provided time
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-wakealarm: The time at which the clock will generate a system wakeup
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+name The name of the RTC corresponding to this sysfs directory
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+since_epoch The number of seconds since the epoch according to the RTC
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+time RTC-provided time
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+wakealarm The time at which the clock will generate a system wakeup
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event. This is a one shot wakeup event, so must be reset
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- after wake if a daily wakeup is required. Format is seconds since
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- the epoch by default, or if there's a leading +, seconds in the
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- future, or if there is a leading +=, seconds ahead of the current
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- alarm.
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-offset: The amount which the rtc clock has been adjusted in firmware.
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+ after wake if a daily wakeup is required. Format is seconds
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+ since the epoch by default, or if there's a leading +, seconds
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+ in the future, or if there is a leading +=, seconds ahead of
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+ the current alarm.
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+offset The amount which the rtc clock has been adjusted in firmware.
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Visible only if the driver supports clock offset adjustment.
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The unit is parts per billion, i.e. The number of clock ticks
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which are added to or removed from the rtc's base clock per
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billion ticks. A positive value makes a day pass more slowly,
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longer, and a negative value makes a day pass more quickly.
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+================ ==============================================================
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-IOCTL INTERFACE
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+IOCTL interface
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---------------
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The ioctl() calls supported by /dev/rtc are also supported by the RTC class
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