Documentation/admin-guide/rtc.rst

8 the local time zone or daylight savings time -- unless they dual boot
9 with MS-Windows -- but will instead be set to Coordinated Universal Time
12 The newest non-PC hardware tends to just count seconds, like the time(2)
13 system call reports, but RTCs also very commonly represent time using
16 Linux has two largely-compatible userspace RTC API families you may
20 	so it's not very portable to non-x86 systems.
35 Old PC/AT-Compatible driver:  /dev/rtc
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44 a few ways (enabling longer alarm periods, and wake-from-hibernate).
59 the type of interrupt (update-done, alarm-rang, or periodic) that was
61 the last read.  Status information is reported through the pseudo-file
67 select(2) on /dev/rtc -- either will block/stop the user process until
69 reasonably high frequency data acquisition where one doesn't want to
72 At high frequencies, or under high loads, the user process should check
75 typical 486-33 running a tight read loop on /dev/rtc will start to suffer
77 frequencies above 1024Hz. So you really should check the high bytes
83 an evil user generating lots of IRQs on a slow 386sx-16, where it might have
85 a different value to /proc/sys/dev/rtc/max-user-freq. Note that the
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111 Because Linux supports many non-ACPI and non-PC platforms, some of which
113 than expecting a single battery-backed MC146818 clone on every system.
128 integrated into embeddable system-on-chip (SOC) processors to discrete chips
130 even support for PC-style RTCs ... including the features exposed on newer PCs
134 example, maybe the low-power battery-backed RTC is a discrete I2C chip, but
135 a high functionality RTC is integrated into the SOC.  That system might read