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.\" Copyright (c) 2018 Ian Lepore <ian@freebsd.org>
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.Dd July 8, 2018
.Dt IMX6_SNVS 4
.Os
.Sh NAME
.Nm imx6_snvs
.Nd device driver for the NXP i.MX6 on-chip Realtime Clock
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device imx6_snvs"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
imx6_snvs_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides
support for the i.MX6 on-chip realtime clock.
It provides the time of day with a resolution of approximately
30 microseconds.
.Pp
.Sq SNVS
stands for Secure Non-Volatile Storage, and refers to the subsystem
within the chip that (optionally) remains powered by a battery when
the rest of the system is powered down.
The on-chip realtime clock is part of that subsystem.
Other features of the SNVS subsystem are related to security, tamper
monitoring, and power control; the
.Nm
driver does not currently support those features.
.Pp
Many i.MX6 systems do not use a battery to provide power to the SNVS
due to its relatively high power draw.  In such systems, this driver
is able to provide a very accurate time following a reboot, but cannot
provide time at all if the power is cycled.  If the system provides an
i2c or other type of alternate realtime clock with lower resolution,
there is value in configuring both clock drivers.
Doing so allows SNVS to provide accurate time after a reboot, while the
external clock provides approximate time after power cycling.
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 12.0 .