Fix typo, and add some additional description to the i8254 and TSC.

PR:		docs/20738
Submitted by:	Tan Koan-Sin <freedom@csie.nctu.edu.tw>

1 files changed, 7 insertions, 4 deletions

diff --git a/share/man/man7/clocks.7 b/share/man/man7/clocks.7
index 018bbaa..5854273 100644
--- a/share/man/man7/clocks.7
+++ b/share/man/man7/clocks.7
@@ -103,7 +103,7 @@ Applications should determine its actual frequency using
 .Xr sysctl 3
 or by reading it from the header in the profiling data file.
 .It
-The mc14618a clock.  This is a real clock with a nominal frequency of
+The mc146818a clock.  This is a real clock with a nominal frequency of
 32768.  It is divided down to give the statistic clock and the profiling
 clock.  It isn't available to applications.
 .It
@@ -122,16 +122,19 @@ by
 applications.
 .It
 The i8254 clock.  This is a real clock/timer with a nominal frequency of
-1193182.  It is divided down to give the scheduling clock.  It isn't
+1193182.  It has three independent time counters to be used.
+It is divided down to give the scheduling clock.  It isn't
 available to applications.
 .It
 The TSC clock (64-bit register) on fifth-generation or later x86 systems.
 This is a real clock with a frequency that is equivalent to the number of
 cycles per second of the CPU(s).
 Its frequency can be found using the sysctl
-.Sy machdep.tsc_freq .
+.Sy machdep.tsc_freq ,
+if it is available.
 It is used to interpolate between values of the scheduling clock.
-It is only available to applications in a purely machine-dependent manner.
+It can be accessed using the PMIOTSTAMP request of
+.Xr perfmon 4 .
 .El
 .Pp
 Summary: if