shithub: 9ferno

ref: 6966e8d72ae8fb72ebf98909acbd464aff84a3cc

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.TH RTC 3
.SH NAME
rtc \- real-time clock and non-volatile memory
.SH SYNOPSIS
.B bind -b '#r' /dev
.PP
.B /dev/rtc
.br
.B /dev/rtcid
.br
.B /dev/nvram
.SH DESCRIPTION
The
.I rtc
device provides access to the real-time clock and any associated non-volatile memory.
Physical devices supported include the Mostek MK48T12-15 Zeropower/Timekeeper,
the Dallas Semiconductor DS1687 real-time clock,
and the IBM PC real-time clock on various platforms.
.PP
The
.B rtc
file when read returns the time as a decimal number, expressed as the number of seconds since the epoch,
1 January 1970 00:00 GMT.
The clock is set by writing the desired number of seconds since the epoch to the file.
Setting the time in this device has no effect on system time returned by
.B /dev/time
(see
.IR cons (3)),
which must be set separately if desired.
For example, when
.I rtc
is available
.I osinit
(see
.IR init (8))
uses it to set
.BR /dev/time .
.PP
The
.B nvram
file provides access to the non-volatile memory commonly implemented
by these clock chips.
There are no cross-platform standards for the range of addresses that
can be safely used by Inferno, or for the content and format of the data.
.PP
The
.B rtcid
file holds a decimal number giving the serial number of the device,
set during manufacturing.
The file exists only if a particular device provides such a number.
.SH SOURCE
.B /os/*/devrtc.c
.SH SEE ALSO
.IR cons (3)
.SH BUGS
The
.B rtc
file returns seconds but
.B /dev/time
returns microseconds: it's history.