Clean up and comment a bit.

diff --git a/sys/arch/mac68k/mac68k/clockreg.h b/sys/arch/mac68k/mac68k/clockreg.h
index 7904b18..d65fde2 100644 (file)
--- a/sys/arch/mac68k/mac68k/clockreg.h
+++ b/sys/arch/mac68k/mac68k/clockreg.h
@@ -1,4 +1,4 @@
-/*     $NetBSD: clockreg.h,v 1.3 1994/10/26 08:46:56 cgd Exp $ */
+/*     $NetBSD: clockreg.h,v 1.4 1996/02/01 03:40:26 briggs Exp $      */
 
 /*-
  * Copyright (C) 1993  Allen K. Briggs, Chris P. Caputo,
@@ -34,18 +34,23 @@
  *
  */
 /*
-   Clock defines and things.
-   MacII clock characteristics used.
-*/
-
-
-#include "../include/limits.h" /* to get CLK_TCK */
+ *  Clock defines and things.
+ *  MacII clock characteristics used.
+ */
 
 
 #define CLK_SPEED      0.0000012766    /* time to complete a clock (3 MHz) */
-#define CLK_INTERVAL   13055           /* clocks to hit CLK_TCK ticks per sec */
-                       /* 7526 for 120 Hz. */
-                       /* 13055 for 60 Hz. */
+#define CLK_INTERVAL   13055           /* clks to hit HZ ticks/sec */
+
+/*
+ * The VIA1 clock speed is 1.2766us, so the timer value above is:
+ *
+ *                    1       1,000,000us     1
+ *  CLK_INTERVAL = -------- * ----------- * ------
+ *                 1.2766us       1s          HZ
+ *
+ * where HZ == 60.  This gives us 13055.5 and change...  We round down.
+ */
 #define CLK_INTH       (CLK_INTERVAL >> 8)
 #define CLK_INTL       (CLK_INTERVAL & 0xff)