Merge pull request #178 from redraw/fix/simulator-watch-rtc-counter

Improved simulator watch RTC counter precision

watch-library/simulator/watch/watch_rtc.c

@@ -22,6 +22,7 @@
  * SOFTWARE.
  */
 #include <limits.h>
+#include <stdbool.h>
 
 #include "watch_rtc.h"
 #include "watch_main_loop.h"
@@ -35,9 +36,10 @@ static const uint32_t RTC_CNT_SUBSECOND_MASK = RTC_CNT_HZ - 1;
 static const uint32_t RTC_CNT_DIV = 7;
 static const uint32_t RTC_CNT_TICKS_PER_MINUTE = RTC_CNT_HZ * 60;
 
-static uint32_t counter_interval;
+static bool rtc_enabled;
 static uint32_t counter;
 static uint32_t reference_timestamp;
+static double next_tick_time;
 
 #define WATCH_RTC_N_COMP_CB 8
 
@@ -66,7 +68,7 @@ static void _watch_process_periodic_callbacks(void);
 static void _watch_process_comp_callbacks(void);
 
 bool _watch_rtc_is_enabled(void) {
-    return counter_interval;
+    return rtc_enabled;
 }
 
 void _watch_rtc_init(void) {
@@ -82,7 +84,7 @@ void _watch_rtc_init(void) {
 
     scheduled_comp_counter = 0;
     counter = 0;
-    counter_interval = 0;
+    rtc_enabled = false;
 
     watch_rtc_set_date_time(watch_get_init_date_time());
     watch_rtc_enable(true);
@@ -164,6 +166,27 @@ void watch_rtc_disable_tick_callback(void) {
     watch_rtc_disable_periodic_callback(1);
 }
 
+static void _watch_schedule_next_tick(void) {
+    if (!rtc_enabled) return;
+
+    double now = EM_ASM_DOUBLE({ return performance.now(); });
+
+    // Target interval in ms
+    double ms = 1000.0 / (double)RTC_CNT_HZ;
+
+    // Schedule next tick, correcting for drift
+    next_tick_time += ms;
+    double delay = next_tick_time - now;
+
+    // If we're behind, reset timing
+    if (delay < 0) {
+        next_tick_time = now + ms;
+        delay = ms;
+    }
+
+    emscripten_async_call(_watch_increase_counter, NULL, delay);
+}
+
 static void _watch_increase_counter(void *userData) {
     (void) userData;
 
@@ -174,6 +197,9 @@ static void _watch_increase_counter(void *userData) {
     _watch_process_comp_callbacks();
 
     resume_main_loop();
+
+    // Schedule the next tick with drift correction
+    _watch_schedule_next_tick();
 }
 
 static void _watch_process_periodic_callbacks(void) {
@@ -338,17 +364,17 @@ void watch_rtc_schedule_next_comp(void) {
 void watch_rtc_enable(bool en)
 {
     // Nothing to do cases
-    if ((en && counter_interval) || (!en && !counter_interval)) {
+    if ((en && rtc_enabled) || (!en && !rtc_enabled)) {
         return;
     }
 
     if (en) {
-        // Very bad way to keep time, but okay way to emulates the hardware.
+        // Use drift-correcting timer instead of fixed setInterval
-        double ms = 1000.0 / (double)RTC_CNT_HZ; // in msec
+        rtc_enabled = true;
-        counter_interval = emscripten_set_interval(_watch_increase_counter, ms, NULL);
+        next_tick_time = EM_ASM_DOUBLE({ return performance.now(); });
+        _watch_schedule_next_tick();
     } else {
-        emscripten_clear_interval(counter_interval);
+        rtc_enabled = false;
-        counter_interval = 0;
     }
 }