- add apm to the GENERIC kernel (disabled by default), and add some comments

regarding apm to LINT
- Disabled the statistics clock on machines which have an APM BIOS and
  have the options "APM_BROKEN_STATCLOCK" enabled (which is default
  in GENERIC now)
- move around some of the code in clock.c dealing with the rtc to make
  it more obvios the effects of disabling the statistics clock

Reviewed by:	bde

sys/amd64/amd64/tsc.c

@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)clock.c	7.2 (Berkeley) 5/12/91
- *	$Id: clock.c,v 1.55 1996/04/05 03:36:31 ache Exp $
+ *	$Id: clock.c,v 1.56 1996/04/05 18:56:10 ache Exp $
  */
 
 /*
@@ -103,6 +103,7 @@ long long	i586_ctr_bias;
 long long	i586_last_tick;
 unsigned long	i586_avg_tick;
 #endif
+int	statclock_disable;
 u_int	stat_imask = SWI_CLOCK_MASK;
 int 	timer0_max_count;
 u_int 	timer0_overflow_threshold;
@@ -123,6 +124,7 @@ static 	u_int	hardclock_max_count;
 static 	void	(*new_function) __P((struct clockframe *frame));
 static 	u_int	new_rate;
 static	u_char	rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
+static	u_char	rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
 static 	char	timer0_state = 0;
 static	char	timer2_state = 0;
 static 	void	(*timer_func) __P((struct clockframe *frame)) = hardclock;
@@ -559,7 +561,7 @@ resettodr()
 	writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */
 
 	/* Reenable RTC updates and interrupts. */
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 /*
@@ -570,8 +572,20 @@ cpu_initclocks()
 {
 	int diag;
 
-	stathz = RTC_NOPROFRATE;
+	if (statclock_disable) {
-	profhz = RTC_PROFRATE;
+		/*
+		 * The stat interrupt mask is different without the
+		 * statistics clock.  Also, don't set the interrupt
+		 * flag which would normally cause the RTC to generate
+		 * interrupts.
+		 */
+		stat_imask = HWI_MASK | SWI_MASK;
+		rtc_statusb = RTCSB_24HR;
+	} else {
+	        /* Setting stathz to nonzero early helps avoid races. */
+		stathz = RTC_NOPROFRATE;
+		profhz = RTC_PROFRATE;
+        }
 
 	/* Finish initializing 8253 timer 0. */
 	register_intr(/* irq */ 0, /* XXX id */ 0, /* flags */ 0,
@@ -591,6 +605,10 @@ cpu_initclocks()
 	/* Initialize RTC. */
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
+
+	/* Don't bother enabling the statistics clock. */
+	if (statclock_disable)
+		return;
 	diag = rtcin(RTC_DIAG);
 	if (diag != 0)
 		printf("RTC BIOS diagnostic error %b\n", diag, RTCDG_BITS);
@@ -598,7 +616,7 @@ cpu_initclocks()
 		      /* XXX */ (inthand2_t *)rtcintr, &stat_imask,
 		      /* unit */ 0);
 	INTREN(IRQ8);
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 void

sys/amd64/conf/GENERIC

@@ -1,7 +1,7 @@
 #
 # GENERIC -- Generic machine with WD/AHx/NCR/BTx family disks
 #
-#	$Id: GENERIC,v 1.65 1996/04/10 23:03:36 jkh Exp $
+#	$Id: GENERIC,v 1.66 1996/04/18 04:02:30 nate Exp $
 #
 
 machine		"i386"
@@ -92,6 +92,12 @@ device		sc0	at isa? port "IO_KBD" tty irq 1 vector scintr
 # Mandatory, don't remove
 device		npx0	at isa? port "IO_NPX" irq 13 vector npxintr
 
+#
+# Laptop support (see LINT for more options)
+#
+device		apm0    at isa?	disable	# Advanced Power Management
+options		APM_BROKEN_STATCLOCK	# Workaround some buggy APM BIOS
+
 device		sio0	at isa? port "IO_COM1" tty irq 4 vector siointr
 device		sio1	at isa? port "IO_COM2" tty irq 3 vector siointr
 device		sio2	at isa? port "IO_COM3" tty irq 5 vector siointr

sys/amd64/include/clock.h

@@ -3,7 +3,7 @@
  * Garrett Wollman, September 1994.
  * This file is in the public domain.
  *
- *	$Id: clock.h,v 1.10 1996/03/31 04:05:17 bde Exp $
+ *	$Id: clock.h,v 1.11 1996/04/05 03:36:20 ache Exp $
  */
 
 #ifndef _MACHINE_CLOCK_H_
@@ -54,6 +54,7 @@
  */
 extern int	adjkerntz;
 extern int	disable_rtc_set;
+extern int	statclock_disable;
 extern int	wall_cmos_clock;
 
 #if defined(I586_CPU) || defined(I686_CPU)

sys/amd64/isa/clock.c

@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)clock.c	7.2 (Berkeley) 5/12/91
- *	$Id: clock.c,v 1.55 1996/04/05 03:36:31 ache Exp $
+ *	$Id: clock.c,v 1.56 1996/04/05 18:56:10 ache Exp $
  */
 
 /*
@@ -103,6 +103,7 @@ long long	i586_ctr_bias;
 long long	i586_last_tick;
 unsigned long	i586_avg_tick;
 #endif
+int	statclock_disable;
 u_int	stat_imask = SWI_CLOCK_MASK;
 int 	timer0_max_count;
 u_int 	timer0_overflow_threshold;
@@ -123,6 +124,7 @@ static 	u_int	hardclock_max_count;
 static 	void	(*new_function) __P((struct clockframe *frame));
 static 	u_int	new_rate;
 static	u_char	rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
+static	u_char	rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
 static 	char	timer0_state = 0;
 static	char	timer2_state = 0;
 static 	void	(*timer_func) __P((struct clockframe *frame)) = hardclock;
@@ -559,7 +561,7 @@ resettodr()
 	writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */
 
 	/* Reenable RTC updates and interrupts. */
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 /*
@@ -570,8 +572,20 @@ cpu_initclocks()
 {
 	int diag;
 
-	stathz = RTC_NOPROFRATE;
+	if (statclock_disable) {
-	profhz = RTC_PROFRATE;
+		/*
+		 * The stat interrupt mask is different without the
+		 * statistics clock.  Also, don't set the interrupt
+		 * flag which would normally cause the RTC to generate
+		 * interrupts.
+		 */
+		stat_imask = HWI_MASK | SWI_MASK;
+		rtc_statusb = RTCSB_24HR;
+	} else {
+	        /* Setting stathz to nonzero early helps avoid races. */
+		stathz = RTC_NOPROFRATE;
+		profhz = RTC_PROFRATE;
+        }
 
 	/* Finish initializing 8253 timer 0. */
 	register_intr(/* irq */ 0, /* XXX id */ 0, /* flags */ 0,
@@ -591,6 +605,10 @@ cpu_initclocks()
 	/* Initialize RTC. */
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
+
+	/* Don't bother enabling the statistics clock. */
+	if (statclock_disable)
+		return;
 	diag = rtcin(RTC_DIAG);
 	if (diag != 0)
 		printf("RTC BIOS diagnostic error %b\n", diag, RTCDG_BITS);
@@ -598,7 +616,7 @@ cpu_initclocks()
 		      /* XXX */ (inthand2_t *)rtcintr, &stat_imask,
 		      /* unit */ 0);
 	INTREN(IRQ8);
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 void

sys/conf/NOTES

@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.248 1996/04/03 00:28:40 gpalmer Exp $
+#	$Id: LINT,v 1.249 1996/04/11 06:19:44 scrappy Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -739,6 +739,14 @@ device pca0 at isa? port IO_TIMER1 tty
 # tw: TW-523 power line interface for use with X-10 home control products
 # si: Specialix SI/XIO 4-32 port terminal multiplexor
 
+#
+# Notes on APM
+#  Some APM implementations will not work with the `statistics clock'
+#  enabled, so it's disabled by default if the APM driver is enabled.
+#  However, this is not true for all laptops.  Try removing the option
+#  APM_BROKEN_STATCLOCK and see if suspend/resume work
+#
+
 #
 # Notes on the spigot:
 #  The video spigot is at 0xad6.  This port address can not be changed.
@@ -775,6 +783,7 @@ device		ctx0	at isa? port 0x230 iomem 0xd0000
 device		spigot0 at isa? port 0xad6 irq 15 iomem 0xee000 vector spigintr
 device		qcam0	at isa? port "IO_LPT3" tty
 device		apm0	at isa?
+options		APM_BROKEN_STATCLOCK
 device		gp0	at isa? port 0x2c0 tty
 device		gsc0	at isa? port "IO_GSC1" tty drq 3
 device		joy0	at isa? port "IO_GAME"

sys/i386/apm/apm.c

@@ -14,7 +14,7 @@
  *
  * Sep, 1994	Implemented on FreeBSD 1.1.5.1R (Toshiba AVS001WD)
  *
- *	$Id: apm.c,v 1.37 1996/03/28 14:28:00 scrappy Exp $
+ *	$Id: apm.c,v 1.38 1996/04/18 19:21:47 nate Exp $
  */
 
 #include "apm.h"
@@ -617,6 +617,9 @@ apmprobe(struct isa_device *dvp)
 		printf("apm: 32-bit connection error.\n");
 		return 0;
 	}
+#ifdef APM_BROKEN_STATCLOCK
+	statclock_disable = 1;
+#endif
 
 	return -1;
 }

sys/i386/bios/apm.c

@@ -14,7 +14,7 @@
  *
  * Sep, 1994	Implemented on FreeBSD 1.1.5.1R (Toshiba AVS001WD)
  *
- *	$Id: apm.c,v 1.37 1996/03/28 14:28:00 scrappy Exp $
+ *	$Id: apm.c,v 1.38 1996/04/18 19:21:47 nate Exp $
  */
 
 #include "apm.h"
@@ -617,6 +617,9 @@ apmprobe(struct isa_device *dvp)
 		printf("apm: 32-bit connection error.\n");
 		return 0;
 	}
+#ifdef APM_BROKEN_STATCLOCK
+	statclock_disable = 1;
+#endif
 
 	return -1;
 }

sys/i386/conf/GENERIC

@@ -1,7 +1,7 @@
 #
 # GENERIC -- Generic machine with WD/AHx/NCR/BTx family disks
 #
-#	$Id: GENERIC,v 1.65 1996/04/10 23:03:36 jkh Exp $
+#	$Id: GENERIC,v 1.66 1996/04/18 04:02:30 nate Exp $
 #
 
 machine		"i386"
@@ -92,6 +92,12 @@ device		sc0	at isa? port "IO_KBD" tty irq 1 vector scintr
 # Mandatory, don't remove
 device		npx0	at isa? port "IO_NPX" irq 13 vector npxintr
 
+#
+# Laptop support (see LINT for more options)
+#
+device		apm0    at isa?	disable	# Advanced Power Management
+options		APM_BROKEN_STATCLOCK	# Workaround some buggy APM BIOS
+
 device		sio0	at isa? port "IO_COM1" tty irq 4 vector siointr
 device		sio1	at isa? port "IO_COM2" tty irq 3 vector siointr
 device		sio2	at isa? port "IO_COM3" tty irq 5 vector siointr

sys/i386/conf/LINT

@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.248 1996/04/03 00:28:40 gpalmer Exp $
+#	$Id: LINT,v 1.249 1996/04/11 06:19:44 scrappy Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -739,6 +739,14 @@ device pca0 at isa? port IO_TIMER1 tty
 # tw: TW-523 power line interface for use with X-10 home control products
 # si: Specialix SI/XIO 4-32 port terminal multiplexor
 
+#
+# Notes on APM
+#  Some APM implementations will not work with the `statistics clock'
+#  enabled, so it's disabled by default if the APM driver is enabled.
+#  However, this is not true for all laptops.  Try removing the option
+#  APM_BROKEN_STATCLOCK and see if suspend/resume work
+#
+
 #
 # Notes on the spigot:
 #  The video spigot is at 0xad6.  This port address can not be changed.
@@ -775,6 +783,7 @@ device		ctx0	at isa? port 0x230 iomem 0xd0000
 device		spigot0 at isa? port 0xad6 irq 15 iomem 0xee000 vector spigintr
 device		qcam0	at isa? port "IO_LPT3" tty
 device		apm0	at isa?
+options		APM_BROKEN_STATCLOCK
 device		gp0	at isa? port 0x2c0 tty
 device		gsc0	at isa? port "IO_GSC1" tty drq 3
 device		joy0	at isa? port "IO_GAME"

sys/i386/conf/NOTES

@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.248 1996/04/03 00:28:40 gpalmer Exp $
+#	$Id: LINT,v 1.249 1996/04/11 06:19:44 scrappy Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -739,6 +739,14 @@ device pca0 at isa? port IO_TIMER1 tty
 # tw: TW-523 power line interface for use with X-10 home control products
 # si: Specialix SI/XIO 4-32 port terminal multiplexor
 
+#
+# Notes on APM
+#  Some APM implementations will not work with the `statistics clock'
+#  enabled, so it's disabled by default if the APM driver is enabled.
+#  However, this is not true for all laptops.  Try removing the option
+#  APM_BROKEN_STATCLOCK and see if suspend/resume work
+#
+
 #
 # Notes on the spigot:
 #  The video spigot is at 0xad6.  This port address can not be changed.
@@ -775,6 +783,7 @@ device		ctx0	at isa? port 0x230 iomem 0xd0000
 device		spigot0 at isa? port 0xad6 irq 15 iomem 0xee000 vector spigintr
 device		qcam0	at isa? port "IO_LPT3" tty
 device		apm0	at isa?
+options		APM_BROKEN_STATCLOCK
 device		gp0	at isa? port 0x2c0 tty
 device		gsc0	at isa? port "IO_GSC1" tty drq 3
 device		joy0	at isa? port "IO_GAME"

sys/i386/i386/tsc.c

@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)clock.c	7.2 (Berkeley) 5/12/91
- *	$Id: clock.c,v 1.55 1996/04/05 03:36:31 ache Exp $
+ *	$Id: clock.c,v 1.56 1996/04/05 18:56:10 ache Exp $
  */
 
 /*
@@ -103,6 +103,7 @@ long long	i586_ctr_bias;
 long long	i586_last_tick;
 unsigned long	i586_avg_tick;
 #endif
+int	statclock_disable;
 u_int	stat_imask = SWI_CLOCK_MASK;
 int 	timer0_max_count;
 u_int 	timer0_overflow_threshold;
@@ -123,6 +124,7 @@ static 	u_int	hardclock_max_count;
 static 	void	(*new_function) __P((struct clockframe *frame));
 static 	u_int	new_rate;
 static	u_char	rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
+static	u_char	rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
 static 	char	timer0_state = 0;
 static	char	timer2_state = 0;
 static 	void	(*timer_func) __P((struct clockframe *frame)) = hardclock;
@@ -559,7 +561,7 @@ resettodr()
 	writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */
 
 	/* Reenable RTC updates and interrupts. */
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 /*
@@ -570,8 +572,20 @@ cpu_initclocks()
 {
 	int diag;
 
-	stathz = RTC_NOPROFRATE;
+	if (statclock_disable) {
-	profhz = RTC_PROFRATE;
+		/*
+		 * The stat interrupt mask is different without the
+		 * statistics clock.  Also, don't set the interrupt
+		 * flag which would normally cause the RTC to generate
+		 * interrupts.
+		 */
+		stat_imask = HWI_MASK | SWI_MASK;
+		rtc_statusb = RTCSB_24HR;
+	} else {
+	        /* Setting stathz to nonzero early helps avoid races. */
+		stathz = RTC_NOPROFRATE;
+		profhz = RTC_PROFRATE;
+        }
 
 	/* Finish initializing 8253 timer 0. */
 	register_intr(/* irq */ 0, /* XXX id */ 0, /* flags */ 0,
@@ -591,6 +605,10 @@ cpu_initclocks()
 	/* Initialize RTC. */
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
+
+	/* Don't bother enabling the statistics clock. */
+	if (statclock_disable)
+		return;
 	diag = rtcin(RTC_DIAG);
 	if (diag != 0)
 		printf("RTC BIOS diagnostic error %b\n", diag, RTCDG_BITS);
@@ -598,7 +616,7 @@ cpu_initclocks()
 		      /* XXX */ (inthand2_t *)rtcintr, &stat_imask,
 		      /* unit */ 0);
 	INTREN(IRQ8);
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 void

sys/i386/include/clock.h

@@ -3,7 +3,7 @@
  * Garrett Wollman, September 1994.
  * This file is in the public domain.
  *
- *	$Id: clock.h,v 1.10 1996/03/31 04:05:17 bde Exp $
+ *	$Id: clock.h,v 1.11 1996/04/05 03:36:20 ache Exp $
  */
 
 #ifndef _MACHINE_CLOCK_H_
@@ -54,6 +54,7 @@
  */
 extern int	adjkerntz;
 extern int	disable_rtc_set;
+extern int	statclock_disable;
 extern int	wall_cmos_clock;
 
 #if defined(I586_CPU) || defined(I686_CPU)

sys/i386/isa/clock.c

@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)clock.c	7.2 (Berkeley) 5/12/91
- *	$Id: clock.c,v 1.55 1996/04/05 03:36:31 ache Exp $
+ *	$Id: clock.c,v 1.56 1996/04/05 18:56:10 ache Exp $
  */
 
 /*
@@ -103,6 +103,7 @@ long long	i586_ctr_bias;
 long long	i586_last_tick;
 unsigned long	i586_avg_tick;
 #endif
+int	statclock_disable;
 u_int	stat_imask = SWI_CLOCK_MASK;
 int 	timer0_max_count;
 u_int 	timer0_overflow_threshold;
@@ -123,6 +124,7 @@ static 	u_int	hardclock_max_count;
 static 	void	(*new_function) __P((struct clockframe *frame));
 static 	u_int	new_rate;
 static	u_char	rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
+static	u_char	rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
 static 	char	timer0_state = 0;
 static	char	timer2_state = 0;
 static 	void	(*timer_func) __P((struct clockframe *frame)) = hardclock;
@@ -559,7 +561,7 @@ resettodr()
 	writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */
 
 	/* Reenable RTC updates and interrupts. */
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 /*
@@ -570,8 +572,20 @@ cpu_initclocks()
 {
 	int diag;
 
-	stathz = RTC_NOPROFRATE;
+	if (statclock_disable) {
-	profhz = RTC_PROFRATE;
+		/*
+		 * The stat interrupt mask is different without the
+		 * statistics clock.  Also, don't set the interrupt
+		 * flag which would normally cause the RTC to generate
+		 * interrupts.
+		 */
+		stat_imask = HWI_MASK | SWI_MASK;
+		rtc_statusb = RTCSB_24HR;
+	} else {
+	        /* Setting stathz to nonzero early helps avoid races. */
+		stathz = RTC_NOPROFRATE;
+		profhz = RTC_PROFRATE;
+        }
 
 	/* Finish initializing 8253 timer 0. */
 	register_intr(/* irq */ 0, /* XXX id */ 0, /* flags */ 0,
@@ -591,6 +605,10 @@ cpu_initclocks()
 	/* Initialize RTC. */
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
+
+	/* Don't bother enabling the statistics clock. */
+	if (statclock_disable)
+		return;
 	diag = rtcin(RTC_DIAG);
 	if (diag != 0)
 		printf("RTC BIOS diagnostic error %b\n", diag, RTCDG_BITS);
@@ -598,7 +616,7 @@ cpu_initclocks()
 		      /* XXX */ (inthand2_t *)rtcintr, &stat_imask,
 		      /* unit */ 0);
 	INTREN(IRQ8);
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 void

sys/isa/atrtc.c

@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)clock.c	7.2 (Berkeley) 5/12/91
- *	$Id: clock.c,v 1.55 1996/04/05 03:36:31 ache Exp $
+ *	$Id: clock.c,v 1.56 1996/04/05 18:56:10 ache Exp $
  */
 
 /*
@@ -103,6 +103,7 @@ long long	i586_ctr_bias;
 long long	i586_last_tick;
 unsigned long	i586_avg_tick;
 #endif
+int	statclock_disable;
 u_int	stat_imask = SWI_CLOCK_MASK;
 int 	timer0_max_count;
 u_int 	timer0_overflow_threshold;
@@ -123,6 +124,7 @@ static 	u_int	hardclock_max_count;
 static 	void	(*new_function) __P((struct clockframe *frame));
 static 	u_int	new_rate;
 static	u_char	rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
+static	u_char	rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
 static 	char	timer0_state = 0;
 static	char	timer2_state = 0;
 static 	void	(*timer_func) __P((struct clockframe *frame)) = hardclock;
@@ -559,7 +561,7 @@ resettodr()
 	writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */
 
 	/* Reenable RTC updates and interrupts. */
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 /*
@@ -570,8 +572,20 @@ cpu_initclocks()
 {
 	int diag;
 
-	stathz = RTC_NOPROFRATE;
+	if (statclock_disable) {
-	profhz = RTC_PROFRATE;
+		/*
+		 * The stat interrupt mask is different without the
+		 * statistics clock.  Also, don't set the interrupt
+		 * flag which would normally cause the RTC to generate
+		 * interrupts.
+		 */
+		stat_imask = HWI_MASK | SWI_MASK;
+		rtc_statusb = RTCSB_24HR;
+	} else {
+	        /* Setting stathz to nonzero early helps avoid races. */
+		stathz = RTC_NOPROFRATE;
+		profhz = RTC_PROFRATE;
+        }
 
 	/* Finish initializing 8253 timer 0. */
 	register_intr(/* irq */ 0, /* XXX id */ 0, /* flags */ 0,
@@ -591,6 +605,10 @@ cpu_initclocks()
 	/* Initialize RTC. */
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
+
+	/* Don't bother enabling the statistics clock. */
+	if (statclock_disable)
+		return;
 	diag = rtcin(RTC_DIAG);
 	if (diag != 0)
 		printf("RTC BIOS diagnostic error %b\n", diag, RTCDG_BITS);
@@ -598,7 +616,7 @@ cpu_initclocks()
 		      /* XXX */ (inthand2_t *)rtcintr, &stat_imask,
 		      /* unit */ 0);
 	INTREN(IRQ8);
-	writertc(RTC_STATUSB, RTCSB_24HR | RTCSB_PINTR);
+	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 void