GPIODCF(4)                OpenBSD Programmer's Manual               GPIODCF(4)

NAME
     gpiodcf - DCF77/HBG timedelta sensor through GPIO pin

SYNOPSIS
     gpiodcf* at gpio? offset 0 mask 0x1
     gpiodcf* at gpio?

DESCRIPTION
     The gpiodcf driver decodes the DCF77 or HBG 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.

     The pin number can be specified in the kernel configuration with the
     offset locator.  The mask locator should always be 0x1 in this case.  The
     offset and mask can also be specified when gpiodcf is attached at runtime
     using the GPIOATTACH ioctl(2) on the gpio(4) device.

     gpiodcf implements a timedelta sensor and the delta (in nanoseconds) be-
     tween the received time information and the local time can be accessed
     through the sysctl(8) interface.  The clock type is indicated in the sen-
     sor description:

           DCF77       German DCF77 time signal station (77.5 kHz longwave
                       transmitter located in Mainflingen near Frankfurt).

           HBG         Swiss HBG time signal station (75 kHz longwave trans-
                       mitter located in Prangins near Geneva).

           Unknown     The clock type has not been determined.

     The quality of the timedelta is reported as the sensor status:

           UNKNOWN     No valid time information has been received yet.

           OK          The time information is valid and the timedelta is safe
                       to use for applications like ntpd(8).

           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.

           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 com-
                       puter internal clocks have a drift.

SEE ALSO
     gpio(4), intro(4), ntpd(8), sysctl(8)

HISTORY
     The gpiodcf driver first appeared in OpenBSD 4.5.

AUTHORS
     The gpiodcf driver was written by Marc Balmer <mbalmer@openbsd.org>.

OpenBSD 4.7                    November 29, 2008                             1
