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+What:           /sys/class/ptp/
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This directory contains files and directories
+                providing a standardized interface to the ancillary
+                features of PTP hardware clocks.
+
+What:           /sys/class/ptp/ptpN/
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This directory contains the attributes of the Nth PTP
+                hardware clock registered into the PTP class driver
+                subsystem.
+
+What:           /sys/class/ptp/ptpN/clock_name
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file contains the name of the PTP hardware clock
+                as a human readable string.
+
+What:           /sys/class/ptp/ptpN/max_adjustment
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file contains the PTP hardware clock's maximum
+                frequency adjustment value (a positive integer) in
+                parts per billion.
+
+What:           /sys/class/ptp/ptpN/n_alarms
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file contains the number of periodic or one shot
+                alarms offer by the PTP hardware clock.
+
+What:           /sys/class/ptp/ptpN/n_external_timestamps
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file contains the number of external timestamp
+                channels offered by the PTP hardware clock.
+
+What:           /sys/class/ptp/ptpN/n_periodic_outputs
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file contains the number of programmable periodic
+                output channels offered by the PTP hardware clock.
+
+What:           /sys/class/ptp/ptpN/pps_avaiable
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file indicates whether the PTP hardware clock
+                supports a Pulse Per Second to the host CPU. Reading
+                "1" means that the PPS is supported, while "0" means
+                not supported.
+
+What:           /sys/class/ptp/ptpN/extts_enable
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This write-only file enables or disables external
+                timestamps. To enable external timestamps, write the
+                channel index followed by a "1" into the file.
+                To disable external timestamps, write the channel
+                index followed by a "0" into the file.
+
+What:           /sys/class/ptp/ptpN/fifo
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This file provides timestamps on external events, in
+                the form of three integers: channel index, seconds,
+                and nanoseconds.
+
+What:           /sys/class/ptp/ptpN/period
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This write-only file enables or disables periodic
+                outputs. To enable a periodic output, write five
+                integers into the file: channel index, start time
+                seconds, start time nanoseconds, period seconds, and
+                period nanoseconds. To disable a periodic output, set
+                all the seconds and nanoseconds values to zero.
+
+What:           /sys/class/ptp/ptpN/pps_enable
+Date:           September 2010
+Contact:        Richard Cochran <richardcochran@gmail.com>
+Description:
+                This write-only file enables or disables delivery of
+                PPS events to the Linux PPS subsystem. To enable PPS
+                events, write a "1" into the file. To disable events,
+                write a "0" into the file.