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)
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
36 --------------------------------------
38 All PCs (even Alpha machines) have a Real Time Clock built into them.
39 Usually they are built into the chipset of the computer, but some may
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
63 built in locking so that only one process is allowed to have the /dev/rtc
67 select(2) on /dev/rtc -- either will block/stop the user process until
75 typical 486-33 running a tight read loop on /dev/rtc will start to suffer
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
97 The alarm and/or interrupt frequency are programmed into the RTC via
109 --------------------------------------------
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