From b38096892ac5ab54dadd7c1aaa11927ac93ae7f3 Mon Sep 17 00:00:00 2001
From: wdk <wdk@NetBSD.org>
Date: Wed, 6 Sep 2000 07:52:47 +0000
Subject: [PATCH] Microtime calculation was seriously incorrect when HZ != 100

Give rest of clock interrupt code a revamp.  Because we are using an external
cycle counter we can now handle loosing several hundred interrupts without
the time slipping.
---
 sys/arch/mipsco/mipsco/machdep.c |  7 ++---
 sys/arch/mipsco/obio/rambo.c     | 49 ++++++++++++++++++++------------
 sys/arch/mipsco/obio/rambo.h     |  5 ++--
 3 files changed, 37 insertions(+), 24 deletions(-)

diff --git a/sys/arch/mipsco/mipsco/machdep.c b/sys/arch/mipsco/mipsco/machdep.c
index fa4b0d4382fd..69596549e750 100644
--- a/sys/arch/mipsco/mipsco/machdep.c
+++ b/sys/arch/mipsco/mipsco/machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: machdep.c,v 1.6 2000/08/29 12:12:59 wdk Exp $	*/
+/*	$NetBSD: machdep.c,v 1.7 2000/09/06 07:52:47 wdk Exp $	*/
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -43,7 +43,7 @@
 
 #include <sys/cdefs.h>			/* RCS ID & Copyright macro defns */
 
-__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.6 2000/08/29 12:12:59 wdk Exp $");
+__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.7 2000/09/06 07:52:47 wdk Exp $");
 
 /* from: Utah Hdr: machdep.c 1.63 91/04/24 */
 
@@ -570,13 +570,12 @@ microtime(tvp)
 {
 	static struct timeval lasttime;
 	int s = splclock();
-	long rambo_getutime();
 
 	*tvp = time;
 
 	tvp->tv_usec += (*platform.clkread)();
 
-	if (tvp->tv_usec >= 1000000) {
+	while (tvp->tv_usec >= 1000000) {
 		tvp->tv_usec -= 1000000;
 		tvp->tv_sec++;
 	}
diff --git a/sys/arch/mipsco/obio/rambo.c b/sys/arch/mipsco/obio/rambo.c
index e30322cc2628..fa826dd76898 100644
--- a/sys/arch/mipsco/obio/rambo.c
+++ b/sys/arch/mipsco/obio/rambo.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: rambo.c,v 1.2 2000/08/15 04:56:47 wdk Exp $	*/
+/*	$NetBSD: rambo.c,v 1.3 2000/09/06 07:52:47 wdk Exp $	*/
 
 /*
  * Copyright (c) 2000 The NetBSD Foundation, Inc.
@@ -104,7 +104,7 @@ rambo_attach(parent, self, aux)
 	/* Setup RAMBO Timer to generate timer interrupts */
 	sc->sc_hzticks = HZ_TO_TICKS(hz);
 
-	sc->sc_tclast = sc->sc_hzticks;
+	sc->sc_tclast = 0;
 	bus_space_write_4(sc->sc_bst, sc->sc_bsh, RB_TCOUNT, 0);
 	bus_space_write_4(sc->sc_bst, sc->sc_bsh, RB_TBREAK, sc->sc_hzticks);
 
@@ -120,36 +120,49 @@ void
 rambo_clkintr(cf)
 	struct clockframe *cf;
 {
-	register u_int32_t tbreak, tclast;
-	register int cycles = 0;
-	
+	register u_int32_t tbreak, tcount;
+	register int delta;
+
 	rambo->sc_intrcnt.ev_count++;
 	tbreak = bus_space_read_4(rambo->sc_bst, rambo->sc_bsh, RB_TBREAK);
-	/* This will also clear the interrupt */
-	while ((tclast=bus_space_read_4(rambo->sc_bst, rambo->sc_bsh,
-					RB_TCOUNT)) >= tbreak) { 
+	tcount = bus_space_read_4(rambo->sc_bst, rambo->sc_bsh,	RB_TCOUNT);
+	delta  = tcount - tbreak;
+
+	if (delta > (rambo->sc_hzticks>>1)) {
+		/*
+		 * Either tcount may overtake the updated tbreak value
+		 * or we have missed several interrupt's
+		 */
+		int cycles = 10 * hz;
+		while (cycles && tbreak < tcount) {
+			hardclock(cf);
+			rambo->sc_tclast = tbreak;
+			tbreak += rambo->sc_hzticks;
+			cycles--;
+		}
+		if (cycles == 0) { /* catchup failed - assume we are in sync */
+			tcount = bus_space_read_4(rambo->sc_bst,
+						  rambo->sc_bsh, RB_TCOUNT);
+			rambo->sc_tclast = tbreak = tcount;
+		}
+	} else {
 		hardclock(cf);
-		tbreak += rambo->sc_hzticks;
-		cycles++;
+		rambo->sc_tclast = tbreak;
 	}
 
+	tbreak += rambo->sc_hzticks;
+
 	bus_space_write_4(rambo->sc_bst, rambo->sc_bsh, RB_TBREAK, tbreak);
-	rambo->sc_tclast = tclast;
 }    
 
 /*
  * Calculate the number of microseconds since the last clock tick
  */
-unsigned
+static unsigned
 rambo_clkread()
 {
         register u_int32_t tcount;
-	register u_int32_t tusec;
 	
-	int s = splclock();
 	tcount = bus_space_read_4(rambo->sc_bst, rambo->sc_bsh, RB_TCOUNT);
-	tusec  = TICKS_TO_USECS(tcount-rambo->sc_tclast, hz);
-	splx(s);
-
-	return tusec;
+	return TICKS_TO_USECS(tcount - rambo->sc_tclast);
 }
diff --git a/sys/arch/mipsco/obio/rambo.h b/sys/arch/mipsco/obio/rambo.h
index bf6b9496c687..0e32f787f60a 100644
--- a/sys/arch/mipsco/obio/rambo.h
+++ b/sys/arch/mipsco/obio/rambo.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: rambo.h,v 1.1 2000/08/12 22:58:58 wdk Exp $	*/
+/*	$NetBSD: rambo.h,v 1.2 2000/09/06 07:52:47 wdk Exp $	*/
 /*-
  * Copyright (c) 2000 The NetBSD Foundation, Inc.
  * All rights reserved.
@@ -115,6 +115,7 @@ struct	rambo_ch {
 #define RB_BMASK	((1<<RB_BSIZE)-1)
 #define	RB_BOUNDRY	(1<<RB_BSIZE)
 
+/* Rambo cycle counter is fed by 25MHz clock then divided by 4 */
 #define	HZ_TO_TICKS(hz)		(6250000L/(hz))
-#define TICKS_TO_USECS(t, hz)	((t)*4/((hz)/4)) /* XXX */
+#define TICKS_TO_USECS(t)	((t*4)/25)
 #endif