From 6ba12646420904a02b9be97c595b3f9cf83e10ff Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Sun, 31 Jan 1999 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1999-01-31

---
 pc/archgeneric.c |  2 +-
 pc/dat.h         |  1 +
 pc/fns.h         |  2 +-
 pc/i8253.c       | 39 +++++++++++++++++++++++++++------------
 4 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/pc/archgeneric.c b/pc/archgeneric.c
index 3ee0ea9524cf7287acd50522070db05f91159a60..03332fb422bf48c1286580440e45a0f79a6c2eb2 100644
--- a/pc/archgeneric.c
+++ b/pc/archgeneric.c
@@ -138,7 +138,7 @@ cpuidentify(void)
 		t++;
 	}
 	m->cpuidtype = t->name;
-	i8253init(t->aalcycles);
+	i8253init(t->aalcycles, t->family >= 5);
 
 	/*
 	 * If machine check exception or page size extensions are supported
diff --git a/pc/dat.h b/pc/dat.h
index eb2954a5b0289911930aa8bdb309c6785f4e705d..6bb941028209254916bbee1857cdfb333d22cdd0 100644
--- a/pc/dat.h
+++ b/pc/dat.h
@@ -179,6 +179,7 @@ struct Mach
 	int	loopconst;
 
 	int	cpumhz;
+	int	cpuhz;
 	int	cpuidax;
 	int	cpuiddx;
 	char	cpuidid[16];
diff --git a/pc/fns.h b/pc/fns.h
index d2113e242f5476d32819c3663b234a2a59940119..453536699cfcc77bd053149abf49472b34694ead 100644
--- a/pc/fns.h
+++ b/pc/fns.h
@@ -34,7 +34,7 @@ char*	getconf(char*);
 int	i8042auxcmd(int);
 void	i8042auxenable(void (*)(int, int));
 void	i8042reset(void);
-void	i8253init(int);
+void	i8253init(int, int);
 void	i8253enable(void);
 uvlong	i8253read(uvlong*);
 void	i8259init(void);
diff --git a/pc/i8253.c b/pc/i8253.c
index eebf08742866c599aa57e211a78538fd87dfee23..0e35c9934c99ebdeab0a3e5d2896c42b2c5de8fd 100644
--- a/pc/i8253.c
+++ b/pc/i8253.c
@@ -27,9 +27,10 @@ enum
 };
 
 void
-i8253init(int aalcycles)
+i8253init(int aalcycles, int havecycleclock)
 {
 	int cpufreq, loops, incr, x, y;
+	vlong a, b;
 	static int initialised;
 
 	if(initialised == 0){
@@ -75,10 +76,14 @@ i8253init(int aalcycles)
 		 *
 		 */
 		outb(Tmode, Latch0);
+		if(havecycleclock)
+			rdmsr(0x10, &a);
 		x = inb(T0cntr);
 		x |= inb(T0cntr)<<8;
 		aamloop(loops);
 		outb(Tmode, Latch0);
+		if(havecycleclock)
+			rdmsr(0x10, &b);
 		y = inb(T0cntr);
 		y |= inb(T0cntr)<<8;
 		x -= y;
@@ -90,22 +95,32 @@ i8253init(int aalcycles)
 			break;
 	}
 
-	/*
-	 *  counter  goes at twice the frequency, once per transition,
-	 *  i.e., twice per square wave
-	 */
-	x >>= 1;
-
 	/*
  	 *  figure out clock frequency and a loop multiplier for delay().
+	 *  n.b. counter goes up by 2*Freq
 	 */
-	cpufreq = loops*((aalcycles*Freq)/x);
+	cpufreq = loops*((aalcycles*2*Freq)/x);
 	m->loopconst = (cpufreq/1000)/aalcycles;	/* AAM+LOOP's for 1 ms */
 
-	/*
-	 *  add in possible 0.5% error and convert to MHz
-	 */
-	m->cpumhz = (cpufreq + cpufreq/200)/1000000;
+	if(havecycleclock){
+
+		/* counter goes up by 2*Freq */
+		b = (b-a)<<1;
+		b *= Freq;
+		b /= x;
+
+		/*
+		 *  round to the nearest megahz
+		 */
+		m->cpumhz = (b+500000)/1000000L;
+		m->cpuhz = b;
+	} else {
+		/*
+		 *  add in possible 0.5% error and convert to MHz
+		 */
+		m->cpumhz = (cpufreq + cpufreq/200)/1000000;
+		m->cpuhz = cpufreq;
+	}
 }
 
 void