svn commit: r286596 - head

[Ian Lepore]

Author: ian
Date: Mon Aug 10 21:09:06 2015
New Revision: 286596
URL: https://svnweb.freebsd.org/changeset/base/286596

Log:
  Document the change in polarity of the uart(4) PPS capture.

Modified:
  head/UPDATING

Modified: head/UPDATING
==============================================================================
--- head/UPDATING	Mon Aug 10 20:54:03 2015	(r286595)
+++ head/UPDATING	Mon Aug 10 21:09:06 2015	(r286596)
@@ -31,6 +31,20 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 11
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20150810:
+	The polarity of Pulse Per Second (PPS) capture events with the
+	uart(4) driver has been corrected.  Prior to this change the PPS
+	"assert" event corresponded to the trailing edge of a positive PPS
+	pulse and the "clear" event was the leading edge of the next pulse.
+
+	As the width of a PPS pulse in a typical GPS receiver is on the
+	order of 1 millisecond, most users will not notice any significant
+	difference with this change.
+
+	Anyone who has compensated for the historical polarity reversal by
+	configuring a negative offset equal to the pulse width will need to
+	remove that workaround.
+
 20150809:
 	The default group assigned to /dev/dri entries has been changed
 	from 'wheel' to 'video' with the id of '44'. If you want to have