1.\" 2.\" Copyright (c) 2018 Ian Lepore <ian@freebsd.org> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd July 8, 2018 29.Dt IMX6_SNVS 4 30.Os 31.Sh NAME 32.Nm imx6_snvs 33.Nd device driver for the NXP i.MX6 on-chip Realtime Clock 34.Sh SYNOPSIS 35To compile this driver into the kernel, 36place the following line in your 37kernel configuration file: 38.Bd -ragged -offset indent 39.Cd "device imx6_snvs" 40.Ed 41.Pp 42Alternatively, to load the driver as a 43module at boot time, place the following line in 44.Xr loader.conf 5 : 45.Bd -literal -offset indent 46imx6_snvs_load="YES" 47.Ed 48.Sh DESCRIPTION 49The 50.Nm 51driver provides 52support for the i.MX6 on-chip realtime clock. 53It provides the time of day with a resolution of approximately 5430 microseconds. 55.Pp 56.Sq SNVS 57stands for Secure Non-Volatile Storage, and refers to the subsystem 58within the chip that (optionally) remains powered by a battery when 59the rest of the system is powered down. 60The on-chip realtime clock is part of that subsystem. 61Other features of the SNVS subsystem are related to security, tamper 62monitoring, and power control; the 63.Nm 64driver does not currently support those features. 65.Pp 66Many i.MX6 systems do not use a battery to provide power to the SNVS 67due to its relatively high power draw. In such systems, this driver 68is able to provide a very accurate time following a reboot, but cannot 69provide time at all if the power is cycled. If the system provides an 70i2c or other type of alternate realtime clock with lower resolution, 71there is value in configuring both clock drivers. 72Doing so allows SNVS to provide accurate time after a reboot, while the 73external clock provides approximate time after power cycling. 74.Sh HISTORY 75The 76.Nm 77driver first appeared in 78.Fx 12.0 . 79