20060303

1 files changed, 283 insertions, 0 deletions

diff --git a/os/port/tod.c b/os/port/tod.c
new file mode 100644
index 00000000..55486453
--- /dev/null
+++ b/os/port/tod.c
@@ -0,0 +1,283 @@
+#include	"u.h"
+#include	"../port/lib.h"
+#include	"mem.h"
+#include	"dat.h"
+#include	"fns.h"
+#include	"../port/error.h"
+
+/* compute nanosecond epoch time from the fastest ticking clock
+ * on the system.  converting the time to nanoseconds requires
+ * the following formula
+ *
+ *	t = (((1000000000<<31)/f)*ticks)>>31
+ *
+ *  where
+ *
+ *	'f'		is the clock frequency
+ *	'ticks'		are clock ticks
+ *
+ *  to avoid too much calculation in todget(), we calculate
+ *
+ *	mult = (1000000000<<32)/f
+ *
+ *  each time f is set.  f is normally set by a user level
+ *  program writing to /dev/fastclock.  mul64fract will then
+ *  take that fractional multiplier and a 64 bit integer and
+ *  return the resulting integer product.
+ *
+ *  We assume that the cpu's of a multiprocessor are synchronized.
+ *  This assumption needs to be questioned with each new architecture.
+ */
+
+/* frequency of the tod clock */
+#define TODFREQ	1000000000ULL
+
+struct {
+	int		init;		// true if initialized
+	ulong	cnt;
+	Lock;
+	uvlong	multiplier;	// t = off + (multiplier*ticks)>>31
+	uvlong	divider;	// ticks = (divider*(ticks-off))>>31
+	vlong	hz;		// frequency of fast clock
+	vlong	last;		// last reading of fast clock
+	vlong	off;		// offset from epoch to last
+	vlong	lasttime;	// last return value from todget
+	vlong	delta;		// add 'delta' each slow clock tick from sstart to send
+	ulong	sstart;		// ...
+	ulong	send;		// ...
+} tod;
+
+void
+todinit(void)
+{
+	if(tod.init)
+		return;
+	ilock(&tod);
+	tod.last = fastticks((uvlong*)&tod.hz);
+	iunlock(&tod);
+	todsetfreq(tod.hz);
+	tod.init = 1;
+	addclock0link(todfix, 100);
+}
+
+/*
+ *  calculate multiplier
+ */
+void
+todsetfreq(vlong f)
+{
+	ilock(&tod);
+	tod.hz = f;
+
+	/* calculate multiplier for time conversion */
+	tod.multiplier = mk64fract(TODFREQ, f);
+	tod.divider = mk64fract(f, TODFREQ);
+
+	iunlock(&tod);
+}
+
+/*
+ *  Set the time of day struct
+ */
+void
+todset(vlong t, vlong delta, int n)
+{
+	if(!tod.init)
+		todinit();
+
+	ilock(&tod);
+	if(t >= 0){
+		tod.off = t;
+		tod.last = fastticks(nil);
+		tod.lasttime = 0;
+		tod.delta = 0;
+		tod.sstart = tod.send;
+	} else {
+		if(n <= 0)
+			n = 1;
+		n *= HZ;
+		if(delta < 0 && n > -delta)
+			n = -delta;
+		if(delta > 0 && n > delta)
+			n = delta;
+		delta = delta/n;
+		tod.sstart = MACHP(0)->ticks;
+		tod.send = tod.sstart + n;
+		tod.delta = delta;
+	}
+	iunlock(&tod);
+}
+
+/*
+ *  get time of day
+ */
+vlong
+todget(vlong *ticksp)
+{
+	uvlong x;
+	vlong ticks, diff;
+	ulong t;
+
+	if(!tod.init)
+		todinit();
+
+	// we don't want time to pass twixt the measuring of fastticks
+	// and grabbing tod.last.  Also none of the vlongs are atomic so
+	// we have to look at them inside the lock.
+	ilock(&tod);
+	tod.cnt++;
+	ticks = fastticks(nil);
+
+	// add in correction
+	if(tod.sstart != tod.send){
+		t = MACHP(0)->ticks;
+		if(t >= tod.send)
+			t = tod.send;
+		tod.off = tod.off + tod.delta*(t - tod.sstart);
+		tod.sstart = t;
+	}
+
+	// convert to epoch
+	diff = ticks - tod.last;
+	if(diff < 0)
+		diff = 0;
+	mul64fract(&x, diff, tod.multiplier);
+	x += tod.off;
+
+	// time can't go backwards
+	if(x < tod.lasttime)
+		x = tod.lasttime;
+	else
+		tod.lasttime = x;
+
+	iunlock(&tod);
+
+	if(ticksp != nil)
+		*ticksp = ticks;
+
+	return x;
+}
+
+/*
+ *  convert time of day to ticks
+ */
+uvlong
+tod2fastticks(vlong ns)
+{
+	uvlong x;
+
+	ilock(&tod);
+	mul64fract(&x, ns-tod.off, tod.divider);
+	x += tod.last;
+	iunlock(&tod);
+	return x;
+}
+
+/*
+ *  called regularly to avoid calculation overflows
+ */
+void
+todfix(void)
+{
+	vlong ticks, diff;
+	uvlong x;
+
+	ticks = fastticks(nil);
+
+	diff = ticks - tod.last;
+	if(diff > tod.hz){
+		ilock(&tod);
+	
+		// convert to epoch
+		mul64fract(&x, diff, tod.multiplier);
+if(x > 30000000000ULL) print("todfix %llud\n", x);
+		x += tod.off;
+	
+		// protect against overflows
+		tod.last = ticks;
+		tod.off = x;
+	
+		iunlock(&tod);
+	}
+}
+
+long
+tseconds(void)
+{
+	vlong x;
+	int i;
+
+	x = todget(nil);
+	x = x/TODFREQ;
+	i = x;
+	return i;
+}
+
+//  convert milliseconds to fast ticks
+//
+uvlong
+ms2fastticks(ulong ms)
+{
+	if(!tod.init)
+		todinit();
+	return (tod.hz*ms)/1000ULL;
+}
+
+/*
+ *  convert nanoseconds to fast ticks
+ */
+uvlong
+ns2fastticks(uvlong ns)
+{
+	uvlong res;
+
+	if(!tod.init)
+		todinit();
+	mul64fract(&res, ns, tod.divider);
+	return res;
+}
+
+/*
+ *  convert fast ticks to ns
+ */
+uvlong
+fastticks2ns(uvlong ticks)
+{
+	uvlong res;
+
+	if(!tod.init)
+		todinit();
+	mul64fract(&res, ticks, tod.multiplier);
+	return res;
+}
+
+/*
+ * Make a 64 bit fixed point number that has a decimal point
+ * to the left of the low order 32 bits.  This is used with
+ * mul64fract for converting twixt nanoseconds and fastticks.
+ *
+ *	multiplier = (to<<32)/from
+ */
+uvlong
+mk64fract(uvlong to, uvlong from)
+{
+/*
+	int shift;
+
+	if(to == 0ULL)
+		return 0ULL;
+
+	shift = 0;
+	while(shift < 32 && to < (1ULL<<(32+24))){
+		to <<= 8;
+		shift += 8;
+	}
+	while(shift < 32 && to < (1ULL<<(32+31))){
+		to <<= 1;
+		shift += 1;
+	}
+
+	return (to/from)<<(32-shift);
+*/
+	return (to<<32)/from;
+}