1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
|
.\"
.\" Copyright (c) 2018 Ian Lepore <ian@freebsd.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.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 .
|
