.\"
.\" Copyright (c) 2014 Luiz Otavio O Souza <loos@freebsd.org>
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.Dd February 12, 2016
.Dt DS3231 4
.Os
.Sh NAME
.Nm ds3231
.Nd Extremely Accurate i2c-integrated RTC/TCXO/Crystal
.Sh SYNOPSIS
.Cd "device iic"
.Cd "device iicbus"
.Cd "device ds3231"
.Sh DESCRIPTION
The
.Nm
is a low-cost, extremely accurate I2C realtime clock (RTC) with an
integrated temperature-compensated crystal oscillator (TCXO) and crystal.
.Pp
The device incorporates a battery input and maintains accurate timekeeping
when main power to the device is interrupted.
.Pp
Access to
.Nm
data is made with the
.Xr sysctl 8
interface:
.Bd -literal
dev.ds3231.0.%desc: Maxim DS3231 RTC
dev.ds3231.0.%driver: ds3231
dev.ds3231.0.%location: addr=0xd0
dev.ds3231.0.%pnpinfo: name=rtc compat=maxim,ds3231
dev.ds3231.0.%parent: iicbus1
dev.ds3231.0.temperature: 23.2C
dev.ds3231.0.temp_conv: 0
dev.ds3231.0.bbsqw: 0
dev.ds3231.0.sqw_freq: 8192
dev.ds3231.0.sqw_mode: interrupt
dev.ds3231.0.32khz_enable: 1
.Ed
.Bl -tag -width ".Va dev.ds3231.%d.temperature"
.It Va dev.ds3231.%d.temperature
The read-only value of the current temperature read by the RTC.
.It Va dev.ds3231.%d.temp_conv
Start a new temperature conversion.
When read as 1, a temperature conversion is in progress.
When read as 0 and then set to 1, a temperature conversion is started.
The temperature conversion runs automatically on power up and once every 64
seconds afterward.
.It Va dev.ds3231.%d.bbsqw
If set to 1 and
.Va dev.ds3231.%d.sqw_mode
is set to square-wave, battery-backed square-wave output is enabled.
If set to 0, the SQW pin will be set to high impendance when the RTC is
being powered by battery.
.It Va dev.ds3231.%d.sqw_freq
Select the frequency of the SQW pin when the square-wave output is enabled on
.Va dev.ds3231.%d.sqw_mode .
It can be set to 1, 1024, 4096, and 8192.
.It Va dev.ds3231.%d.sqw_mode
Set the operation mode for the SQW pin.
It can be set to 'interrupt' (default) or 'square-wave'.
In interrupt mode, the SQW pin is used to generate interrupts for the RTC
alarms.
In square-wave mode, the SQW pin drives a square-wave of
.Va dev.ds3231.%d.sqw_freq
frequency.
.It Va dev.ds3231.%d.32khz_enable
Enable the 32kHz output.
.El
.Pp
Please check the
.Nm
datasheet for more details.
.Pp
On a
.Xr device.hints 5
based system, such as
.Li MIPS ,
these values are configurable for
.Nm :
.Bl -tag -width ".Va hint.ds3231.%d.addr"
.It Va hint.ds3231.%d.at
The
.Xr iicbus 4
that the
.Nm
is connected to.
.It Va hint.ds3231.%d.addr
The 8-bit i2c address of
.Nm .
The default 8-bit address for
.Nm
is 0xd0.
.El
.Pp
On a
.Xr FDT 4
based system the following properties must be set:
.Bl -tag -width ".Va compatible"
.It Va compatible
Must always be set to "maxim,ds3231".
.It Va reg
The 7-bit i2c address of
.Nm .
The default 7-bit address for
.Nm
is 0x68.
.El
.Sh SEE ALSO
.Xr fdt 4 ,
.Xr iic 4 ,
.Xr iicbus 4 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 11.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver and this manual page were written by
.An Luiz Otavio O Souza Aq Mt loos@FreeBSD.org .