79 lines
2.9 KiB
Groff
79 lines
2.9 KiB
Groff
.\"
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.\" Copyright (c) 2018 Ian Lepore <ian@freebsd.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 8, 2018
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.Dt IMX6_SNVS 4
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.Os
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.Sh NAME
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.Nm imx6_snvs
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.Nd device driver for the NXP i.MX6 on-chip Realtime Clock
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.Sh SYNOPSIS
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To compile this driver into the kernel,
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place the following line in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device imx6_snvs"
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.Ed
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.Pp
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Alternatively, to load the driver as a
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module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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imx6_snvs_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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driver provides
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support for the i.MX6 on-chip realtime clock.
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It provides the time of day with a resolution of approximately
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30 microseconds.
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.Pp
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.Sq SNVS
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stands for Secure Non-Volatile Storage, and refers to the subsystem
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within the chip that (optionally) remains powered by a battery when
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the rest of the system is powered down.
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The on-chip realtime clock is part of that subsystem.
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Other features of the SNVS subsystem are related to security, tamper
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monitoring, and power control; the
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.Nm
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driver does not currently support those features.
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.Pp
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Many i.MX6 systems do not use a battery to provide power to the SNVS
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due to its relatively high power draw. In such systems, this driver
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is able to provide a very accurate time following a reboot, but cannot
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provide time at all if the power is cycled. If the system provides an
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i2c or other type of alternate realtime clock with lower resolution,
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there is value in configuring both clock drivers.
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Doing so allows SNVS to provide accurate time after a reboot, while the
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external clock provides approximate time after power cycling.
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 12.0 .
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