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 either
+ seconds since the epoch or, if there's a leading +, seconds
+ in the future.
+
+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
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, it probably
- also offers update IRQs whenever the "seconds" counter changes.
- If needed, the RTC framework can emulate this mechanism.
+ * 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 ... another
- feature often accessible with an IRQ line is a periodic IRQ, issued
- at settable frequencies (usually 2^N Hz).
+ * 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 need not actually be implemented by your
-driver. The common rtc-dev interface handles many of these nicely if your
-driver returns ENOIOCTLCMD. Some common examples:
+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: the
- set_alarm/read_alarm functions will be called.
+ * 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: the irq_set_freq function will be called
- to set the frequency while the framework will handle the read for you
- since the frequency is stored in the irq_freq member of the rtc_device
- structure. Your driver needs to initialize the irq_freq member during
- init. Make sure you check the requested frequency is in range of your
- hardware in the irq_set_freq function. If it isn't, return -EINVAL. If
- you cannot actually change the frequency, do not define irq_set_freq.
+ * RTC_IRQP_SET, RTC_IRQP_READ: These are emulated by the generic code.
- * RTC_PIE_ON, RTC_PIE_OFF: the irq_set_state function will be called.
+ * RTC_PIE_ON, RTC_PIE_OFF: These are also emulated by the generic code.
If all else fails, check out the rtc-test.c driver!
projects / linux-flexiantxendom0.git / blobdiff