From ebdcc291b2f26201516fe3d3959cc7a718071b64 Mon Sep 17 00:00:00 2001
From: briggs <briggs@openbsd.org>
Date: Thu, 1 Feb 1996 05:05:19 +0000
Subject: [PATCH] Clean up and comment a bit.

---
 sys/arch/mac68k/mac68k/clockreg.h | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/sys/arch/mac68k/mac68k/clockreg.h b/sys/arch/mac68k/mac68k/clockreg.h
index 7904b1810d9..d65fde29b12 100644
--- 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)
 
-- 
2.20.1