.\" $NetBSD: gpiopps.4,v 1.3 2021/08/07 19:41:13 andvar Exp $
.\"
.\" Copyright (c) 2016 Brad Spencer <brad@anduin.eldar.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd May 11, 2018
.Dt GPIOPPS 4
.Os
.Sh NAME
.Nm gpiopps
.Nd install a PPS handler on GPIO pins
.Sh SYNOPSIS
.Cd "gpiopps* at gpio? offset 0 mask 0x1 flag 0x0"
.Sh DESCRIPTION
The
.Nm
driver provides a 1PPS handler using the PPSAPI on one or two GPIO pins.
.Pp
The base pin number is specified in the kernel configuration file with the
.Ar offset
locator.
The
.Ar mask
should have 1 or 2 bits set, indicating which pins offset from the
base pin should be used
.Pq 0 .. 31 .
Pin configurations are discussed below.
.Pp
The
.Ar flag
locator modifies the pin configuration:
.Bl -tag -width "XXXXXXXX"
.It Dv 0x01
The PPS ASSERT signal should be triggered on the negative
.Pq falling
edge of the
assert pin.
The default is to trigger on the positive
.Pq rising
edge of the pin.
.It Dv 0x02
By default,
.Nm
will use double-edge triggering when only a single pin is specified
and the underlying GPIO hardware supports it.
This flag disables the use of double-edge triggering.
.El
.Pp
If a single pin is specified,
.Nm
uses double-edge triggering to support ASSERT and CLEAR PPS signals.
If the underlying GPIO hardware does not support double-edge triggering,
or if this feature is diabled in the
.Ar flag
locator, then only ASSERT will be signaled on the specified edge.
.Pp
If two pins are specified, the first pin is used to trigger the
ASSERT signal and the second pin is used to trigger the CLEAR
signal.
The ASSERT pin's trigger edge is specified by by the
.Ar flag
locator, and the CLEAR pin triggers on the opposite edge.
This allows ASSERT and CLEAR signals to be triggered even if the underlying
GPIO hardware does not support double-edge triggering.
In this scenario, both GPIO pins would be connected in parallel to the
device sending the 1PPS signals.
.Pp
The
.Ar offset ,
.Ar mask ,
and
.Ar flag
locators can also be specified when
.Nm
is attached at runtime using the
.Dv GPIOATTACH
.Xr ioctl 2
on the
.Xr gpio 4
device.
.Sh SEE ALSO
.Xr gpio 4 ,
.Xr drvctl 8 ,
.Xr gpioctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Nx 9.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Brad Spencer Aq Mt brad@anduin.eldar.org .