diff options
Diffstat (limited to 'Documentation/rtc.txt')
| -rw-r--r-- | Documentation/rtc.txt | 41 |
1 files changed, 17 insertions, 24 deletions
diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt index 9104c106208..596b60c08b7 100644 --- a/Documentation/rtc.txt +++ b/Documentation/rtc.txt @@ -119,8 +119,9 @@ three different userspace interfaces: * /sys/class/rtc/rtcN ... sysfs attributes support readonly access to some RTC attributes. - * /proc/driver/rtc ... the first RTC (rtc0) may expose itself - using a procfs interface. More information is (currently) shown + * /proc/driver/rtc ... the system clock RTC may expose itself + using a procfs interface. If there is no RTC for the system clock, + rtc0 is used by default. More information is (currently) shown here than through sysfs. The RTC Class framework supports a wide variety of RTCs, ranging from those @@ -152,9 +153,10 @@ 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. + 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. IOCTL INTERFACE --------------- @@ -178,38 +180,29 @@ RTC class framework, but can't be supported by the older driver. 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! |