Advantech RSB-4210 Evaluation Kit User Manual download pdf (Page 87)

79 RSB-4210 User Manual

Chapter 3 Software Functionality

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 frame-

work. 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, it probably also

offers update IRQs whenever the "seconds" counter changes. If needed, the RTC

framework can 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).

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 ENOI-

OCTLCMD. 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.

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Advantech RSB-4210 Evaluation Kit User Manual Page 87