Core structure and functions to support a feed-forward clock within the kernel.

Implement ffcounter, a monotonically increasing cumulative counter on top of the
active timecounter. Provide low-level functions to read the ffcounter and
convert it to absolute time or a time interval in seconds using the current
ffclock estimates, which track the drift of the oscillator. Add a ring of
fftimehands to track passing of time on each kernel tick and pick up updates of
ffclock estimates.

Committed on behalf of Julien Ridoux and Darryl Veitch from the University of
Melbourne, Australia, as part of the FreeBSD Foundation funded "Feed-Forward
Clock Synchronization Algorithms" project.

For more information, see http://www.synclab.org/radclock/

Submitted by:	Julien Ridoux (jridoux at unimelb edu au)

2 files changed, 9 insertions, 0 deletions

diff --git a/sys/conf/NOTES b/sys/conf/NOTES
index faf1d25d5787..fa3e374f7bfc 100644
--- a/sys/conf/NOTES
+++ b/sys/conf/NOTES
@@ -1186,6 +1186,14 @@ options 	HZ=100
 
 options 	PPS_SYNC
 
+# Enable support for generic feed-forward clocks in the kernel.
+# The feed-forward clock support is an alternative to the feedback oriented
+# ntpd/system clock approach, and is to be used with a feed-forward
+# synchronization algorithm such as the RADclock:
+# More info here: http://www.synclab.org/radclock
+
+options 	FFCLOCK
+
 
 #####################################################################
 # SCSI DEVICES
diff --git a/sys/conf/options b/sys/conf/options
index 99d64bb613ba..02b908a69178 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -80,6 +80,7 @@ COMPRESS_USER_CORES opt_core.h
 CY_PCI_FASTINTR
 DEADLKRES	opt_watchdog.h
 DIRECTIO
+FFCLOCK
 FULL_PREEMPTION	opt_sched.h
 IPI_PREEMPTION	opt_sched.h
 GEOM_AES	opt_geom.h