Update the Watchdog example

examples/C/src/watchdog/Watchdog.lf

@@ -1,18 +1,23 @@
 /**
  * @brief Demonstration of watchdogs in LF.
  *
- * This program has a periodic source that triggers events every 500 ms, but where every fourth
- * event is delayed before being delivered to the downstream Watcher. This delay models either
- * communication or computation time.
+ * This program has a periodic source that sends events every 500 ms, but where every fourth event
+ * is delayed 300ms in physical time before being delivered to the downstream Watcher. This delay
+ * models either communication or computation time.
  *
- * The Watcher has a deadline of 200 ms. It wants to see events within 200 ms of their logical time,
- * but, because of the delay every fourth event, the deadline will be violated. The deadline
- * violation handler is invoked in this case, but it is only invoked after the event arrives, which
- * is late. What if we need to react to the deadline violation sooner, e.g. in order to drive an
- * actuator?
+ * The Watcher has a deadline of 250 ms. It wants to see events within 250 ms of their logical time,
+ * but, because of the delay every fourth event, the deadline will be violated by those events. The
+ * deadline violation handler is invoked in this case, but it is only invoked after the event
+ * arrives, which is more than 800 ms in physical time after the previous input. What if this input
+ * never arrives or we need to react to the deadline violation sooner, e.g. in order to drive an
+ * actuator? This program ensures that the Watcher will produce an output no later than about 750 ms
+ * in physical time after the previous output. The logical time of the output will be offset by 250
+ * ms.
  *
- * To handle this, the Watcher includes watchdog named "dog" that triggers if any input event is
- * more than 250 ms late.
+ * To handle this, the Watcher includes watchdog named `dog` that triggers if 750 ms have elapsed in
+ * physical time since the last input. When the watchdog triggers, it prints a message and produces
+ * an output immediately, which is 750 ms in logical time (and roughly the same in physical time)
+ * after the previous output.
  *
  * @author Benjamin Asch
  * @author Edward A. Lee
@@ -39,42 +44,40 @@ reactor Watcher {
   input in: int
   output out: int
   state count: int = 1
-  logical action a(500 ms)
 
-  watchdog dog(750 ms) {=
+  watchdog dog(0 ms) {=
     instant_t p = lf_time_physical_elapsed();
     lf_print("******** Watchdog timed out at elapsed physical time: " PRINTF_TIME, p);
   =}
 
   reaction(in) -> dog, out {=
     // Reset the watchdog.  The next event is expected in 500 ms.
     // This watchdog will trigger if the event does not arrive within 750 ms from now,
-    // or is more than 250 ms late.
-    lf_watchdog_start(dog, 0);
+    // (is more than 250 ms late).
+    lf_watchdog_start(dog, MSEC(750));
+    lf_print("Watcher received input %d. Count: %d. Logical time: " PRINTF_TIME,
+        in->value, self->count, lf_time_logical_elapsed());
     lf_print("Watchdog started at physical time " PRINTF_TIME, lf_time_physical_elapsed());
-    lf_print("Will expire at " PRINTF_TIME, lf_time_logical_elapsed() + MSEC(750));
+    lf_print("Will expire at physical time " PRINTF_TIME, lf_time_logical_elapsed() + MSEC(750));
     lf_set(out, in->value);
     self->count++;
-  =} deadline(200 ms) {=
-    // This input is more than 200 ms late. It must have been from the slow cycles.
+  =} deadline(250 ms) {=
+    // This input is more than 250 ms late. It must have been from the slow cycles.
     lf_print("Watcher received late input %d. Ignoring it.", in->value);
   =}
 
-  reaction(dog) -> a {=
+  reaction(dog) -> out, dog {=
     // Note that this reaction will trigger at the earliest available tag, which
-    // will be one microstep later than the most recent input or watchdog violation.
-    lf_print("******** Watchdog triggered. Scheduling output for next logical time.");
-    // Use a logical action so that the logical time of the output aligns.
-    lf_schedule(a, 0);
-  =}
-
-  reaction(a) -> out, dog {=
-    lf_print("******** Backup output being produced.");
+    // will be one microstep later than the most recent input.
+    tag_t tag = lf_tag();
+    instant_t start = lf_time_start();
+    lf_print("******** Watchdog triggered reaction at " PRINTF_TAG ". Producing backup output %d." PRINTF_TIME,
+        tag.time - start, tag.microstep, self->count);
     lf_set(out, self->count++);
     // Start another watchdog cycle in case the very next input is also delayed.
-    lf_watchdog_start(dog, 0);
+    lf_watchdog_start(dog, MSEC(500));
     lf_print("Watchdog started at physical time " PRINTF_TIME, lf_time_physical_elapsed());
-    lf_print("Will expire at " PRINTF_TIME, lf_time_logical_elapsed() + MSEC(750));
+    lf_print("Will expire at physical time " PRINTF_TIME, lf_time_logical_elapsed() + MSEC(500));
   =}
 
   reaction(shutdown) -> dog {=