Copyright (c) 2008 Marc Balmer <mbalmer@openbsd.org>
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.Dd $Mdocdate: July 16 2013 $ .Dt GPIODCF 4 .Os .Sh NAME .Nm gpiodcf .Nd DCF77 timedelta sensor through GPIO pin .Sh SYNOPSIS .Cd "gpiodcf* at gpio? offset 0 mask 0x1" .Cd "gpiodcf* at gpio?" .Sh DESCRIPTION The .Nm driver decodes the DCF77 time signal code using one GPIO pin. The pin is used as a data signal. The GPIO pin must be able to read an input.
p The pin number can be specified in the kernel configuration with the .Ar offset locator. The .Ar mask locator should always be 0x1 in this case. The .Ar offset and .Ar mask can also be specified when .Nm is attached at runtime using the .Dv GPIOATTACH .Xr ioctl 2 on the .Xr gpio 4 device.
p .Nm implements a timedelta sensor and the delta (in nanoseconds) between the received time information and the local time can be accessed through the .Xr sysctl 8 interface. The clock type is indicated in the sensor description: l -tag -width "CRITICALXX" -offset indent t DCF77 German DCF77 time signal station (77.5 kHz longwave transmitter located in Mainflingen near Frankfurt). .El
p The quality of the timedelta is reported as the sensor status: l -tag -width "CRITICALXX" -offset indent t UNKNOWN No valid time information has been received yet. t OK The time information is valid and the timedelta is safe to use for applications like .Xr ntpd 8 . t WARN The time information is still valid, but no new time information has been decoded for at least 5 minutes due to a reception or parity error. The timedelta should be used with care. t CRITICAL No valid time information has been received for more than 15 minutes since the sensor state degraded from OK to WARN. This is an indication that hardware should be checked to see if it is still functional. The timedelta will eventually degrade to a lie as all computer internal clocks have a drift. .El .Sh SEE ALSO .Xr gpio 4 , .Xr intro 4 , .Xr ntpd 8 , .Xr sysctl 8 .Sh HISTORY The .Nm driver first appeared in .Ox 4.5 . .Sh AUTHORS .An -nosplit The .Nm driver was written by .An Marc Balmer Aq Mt mbalmer@openbsd.org .