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From: Ed Schouten <ed@FreeBSD.org>
Date: Wed, 21 Dec 2011 16:47:01 +0000 (UTC)
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Subject: svn commit: r228782 - head/sys/boot/i386/libi386
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Author: ed
Date: Wed Dec 21 16:47:01 2011
New Revision: 228782
URL: http://svn.freebsd.org/changeset/base/228782

Log:
  Make the RTC checking for QEMU even more aggressive.
  
  At work, where we use use KVM+QEMU, we notice that pxeboot is pratically
  impossible because of network timeouts. This is due to the fact that the
  RTC code makes aggressive jumps.
  
  Two RTC reads does not seem to be sufficient. Change the code to check
  for 8 identical RTC values.
  
  Sponsored by:	Kumina bv

Modified:
  head/sys/boot/i386/libi386/time.c

Modified: head/sys/boot/i386/libi386/time.c
==============================================================================
--- head/sys/boot/i386/libi386/time.c	Wed Dec 21 16:38:37 2011	(r228781)
+++ head/sys/boot/i386/libi386/time.c	Wed Dec 21 16:47:01 2011	(r228782)
@@ -62,7 +62,7 @@ bios_seconds(void)
  * Some BIOSes (notably qemu) don't correctly read the RTC
  * registers in an atomic way, sometimes returning bogus values.
  * Therefore we "debounce" the reading by accepting it only when
- * we got two identical values in succession.
+ * we got 8 identical values in succession.
  *
  * If we pass midnight, don't wrap back to 0.
  */
@@ -71,14 +71,16 @@ time(time_t *t)
 {
     static time_t lasttime;
     time_t now, check;
-    int try;
+    int same, try;
 
-    try = 0;
+    same = try = 0;
     check = bios_seconds();
     do {
 	now = check;
 	check = bios_seconds();
-    } while (now != check && ++try < 1000);
+	if (check != now)
+	    same = 0;
+    } while (++same < 8 && ++try < 1000);
 
     if (now < lasttime)
 	now += 24 * 3600;