NAME
gpiodcf —
DCF77 timedelta sensor through GPIO
pin
SYNOPSIS
gpiodcf* at gpio? offset 0 mask 0x1
gpiodcf* at gpio?
DESCRIPTION
The gpiodcf 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.
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) between the received time information and the
local time can be accessed through the
sysctl(8)
interface. The clock type is indicated in the sensor description:
- DCF77
- German DCF77 time signal station (77.5 kHz longwave transmitter located in Mainflingen near Frankfurt).
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 computer internal clocks have a drift.
SEE ALSO
HISTORY
The gpiodcf driver first appeared in
OpenBSD 4.5.
AUTHORS
The gpiodcf driver was written by
Marc Balmer
<mbalmer@openbsd.org>.