score: Port large time delta support to RTEMS

1 files changed, 37 insertions, 5 deletions

diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
index 096de85880..c013c16f87 100644
--- a/cpukit/score/src/kern_tc.c
+++ b/cpukit/score/src/kern_tc.c
@@ -170,7 +170,7 @@ struct timehands {
 	int64_t			th_adjustment;
 #endif /* __rtems__ */
 	uint64_t		th_scale;
-	u_int			th_large_delta;
+	uint32_t		th_large_delta;
 	uint32_t	 	th_offset_count;
 	struct bintime		th_offset;
 	struct bintime		th_bintime;
@@ -226,6 +226,7 @@ static struct timehands th0 = {
 	.th_counter = &dummy_timecounter,
 	.th_scale = (uint64_t)-1 / 1000000,
 	.th_offset = { .sec = 1 },
+	.th_large_delta = 1000000,
 	.th_generation = UINT_MAX,
 #ifdef __rtems__
 	.th_bintime = { .sec = TOD_SECONDS_1970_THROUGH_1988 },
@@ -381,7 +382,12 @@ bintime_off(struct bintime *bt, u_int off)
 	struct timehands *th;
 	struct bintime *btp;
 	uint64_t scale, x;
+#ifndef __rtems__
 	u_int delta, gen, large_delta;
+#else /* __rtems__ */
+	uint32_t delta, large_delta;
+	u_int gen;
+#endif /* __rtems__ */
 
 	do {
 		th = timehands;
@@ -544,17 +550,30 @@ sbintime_t
 _Timecounter_Sbinuptime(void)
 {
 	struct timehands *th;
-	uint32_t gen;
 	sbintime_t sbt;
+	uint64_t scale;
+	uint32_t delta;
+	uint32_t large_delta;
+	u_int gen;
 
 	do {
 		th = timehands;
 		gen = atomic_load_acq_int(&th->th_generation);
 		sbt = bttosbt(th->th_offset);
-		sbt += (th->th_scale * tc_delta(th)) >> 32;
+		scale = th->th_scale;
+		delta = tc_delta(th);
+		large_delta = th->th_large_delta;
 		atomic_thread_fence_acq();
 	} while (gen == 0 || gen != th->th_generation);
 
+	if (__predict_false(delta >= large_delta)) {
+		/* Avoid overflow for scale * delta. */
+		sbt += (scale >> 32) * delta;
+		sbt += ((scale & 0xffffffff) * delta) >> 32;
+	} else {
+		sbt += (scale * delta) >> 32;
+	}
+
 	return (sbt);
 }
 #endif /* __rtems__ */
@@ -1649,12 +1668,24 @@ _Timecounter_Windup(struct bintime *new_boottimebin,
 #ifndef __rtems__
 		tc_min_ticktock_freq = max(1, timecounter->tc_frequency /
 		    (((uint64_t)timecounter->tc_counter_mask + 1) / 3));
+#else /* __rtems__ */
+		/*
+		 * For RTEMS, we can do the scale and large delta calculation
+		 * here, since we do not support th_adjustment.  It is
+		 * condsidered to be zero.
+		 */
+		scale = (uint64_t)1 << 63;
+		scale /= th->th_counter->tc_frequency;
+		th->th_scale = scale * 2;
+		th->th_large_delta = MIN(((uint64_t)1 << 63) / scale,
+		    UINT_MAX);
 #endif /* __rtems__ */
 #ifdef FFCLOCK
 		ffclock_change_tc(th);
 #endif
 	}
 
+#ifndef __rtems__
 	/*-
 	 * Recalculate the scaling factor.  We want the number of 1/2^64
 	 * fractions of a second per period of the hardware counter, taking
@@ -1679,12 +1710,13 @@ _Timecounter_Windup(struct bintime *new_boottimebin,
 	 *
 	 */
 	scale = (uint64_t)1 << 63;
-#ifndef __rtems__
 	scale += (th->th_adjustment / 1024) * 2199;
-#endif /* __rtems__ */
 	scale /= th->th_counter->tc_frequency;
 	th->th_scale = scale * 2;
 	th->th_large_delta = MIN(((uint64_t)1 << 63) / scale, UINT_MAX);
+#else
+	/* See above "Now is a good time to change timecounters." */
+#endif /* __rtems__ */
 
 	/*
 	 * Now that the struct timehands is again consistent, set the new