From: idgay <idgay>
Date: Fri, 11 Aug 2006 20:46:23 +0000 (+0000)
Subject: a bug fix got lost
X-Git-Tag: tinyos/2.0.1~290
X-Git-Url: https://oss.titaniummirror.com/gitweb/?a=commitdiff_plain;h=7c08ae5f79c9791d10a7798df5ebfb80505d91f2;p=tinyos-2.x.git

a bug fix got lost
simplify logic
---

diff --git a/tos/chips/atm128/timer/Atm128AlarmC.nc b/tos/chips/atm128/timer/Atm128AlarmC.nc
index 4bd2e7ac..b16f7844 100644
--- a/tos/chips/atm128/timer/Atm128AlarmC.nc
+++ b/tos/chips/atm128/timer/Atm128AlarmC.nc
@@ -72,43 +72,31 @@ implementation
   }
 
   async command void Alarm.startAt( timer_size t0, timer_size dt ) {
-    /* We don't set an interrupt before "now" + mindt to avoid setting an
-       interrupt which is in the past by the time we actually set
-       it. mindt should always be at least 2, because you cannot set an
-       interrupt one cycle in the future. mindt should also be large enough
-       to cover the execution time of this function. */
+    /* We don't set an interrupt before "now" + mindt to avoid setting
+       an interrupt which is in the past by the time we actually set
+       it. mindt should always be at least 2, because you cannot
+       reliably set an interrupt one cycle in the future. mindt should
+       also be large enough to cover the execution time of this
+       function. */
     atomic
       {
-	timer_size now, expires, minExpires, guardedExpires;
+	timer_size now, elapsed, expires;
 
-	dbg("Atm128AlarmC", "   starting timer at %llu with dt %llu\n", (uint64_t)t0, (uint64_t) dt);
+	dbg("Atm128AlarmC", "   starting timer at %llu with dt %llu\n",
+	    (uint64_t)t0, (uint64_t) dt);
 
-	if (dt < mindt) /* guardedExpires should not be less than t0 */
-	  dt = mindt;
-	expires = t0 + dt;
-	guardedExpires = expires - mindt;
 	now = call HplAtm128Timer.get();
-	minExpires = now + mindt;
-
-	/* t0 is assumed to be in the past. If it's numerically greater
-	   than now, that just represents a time one wrap-around
-	   ago. This requires handling the t0 <= now and t0 > now cases
-	   separately. */
-	if (t0 <= now)
-	  {
-	    /* if it's in the past or the near future, fire now (i.e., test
-	       guardedExpires <= now in wrap-around arithmetic). */
-	    if (guardedExpires >= t0 && // if it wraps, it's > now
-		guardedExpires <= now)
-	      expires = minExpires;
-	  }
+	elapsed = now + mindt - t0;
+	if (elapsed >= dt)
+	  expires = now + mindt;
 	else
-	  {
-	    /* again, guardedExpires <= now in wrap-around arithmetic */
-	    if (guardedExpires >= t0 || // didn't wrap so < now
-		guardedExpires <= now)
-	      expires = minExpires;
-	  }
+	  expires = t0 + dt;
+
+	/* Setting the compare register to "-1" is a bad idea
+	   (interrupt fires before counter overflow is detected, and all
+	   the "current time" stuff goes bad) */
+	if (expires == 0)
+	  expires = 1;
 
 	/* Note: all HplAtm128Compare.set values have one subtracted,
 	   because the comparisons are continuous, but the actual