Fix VBL interval disappearing in realtime mode

core/timermanager.cpp

@@ -101,8 +101,14 @@ uint64_t TimerManager::process_timers()
         if (cur_timer->interval_ns) {
             std::lock_guard<std::recursive_mutex> lk(this->timer_queue.get_mtx());
             uint64_t timeout_ns_new = timeout_ns + cur_timer->interval_ns;
-            if (timeout_ns_new <= time_now)
-                timeout_ns_new = time_now + cur_timer->interval_ns;
+            if (timeout_ns_new <= time_now) {
+                // Skip missed periods without changing the timer's phase.
+                // Rebasing deadlines on time_now would align timers that
+                // have the same period.
+                const uint64_t periods_to_skip =
+                    ((time_now - timeout_ns_new) / cur_timer->interval_ns) + 1;
+                timeout_ns_new += periods_to_skip * cur_timer->interval_ns;
+            }
             cur_timer->timeout_ns = timeout_ns_new;
             this->timer_queue.push(cur_timer);
         } else {

devices/video/videoctrl.cpp

@@ -102,27 +102,30 @@ void VideoCtrlBase::start_refresh_task() {
     this->display.configure(this->active_width, this->active_height);
 
     uint64_t refresh_interval = static_cast<uint64_t>(1.0f / refresh_rate * NS_PER_SEC + 0.5);
-    TimerManager::get_instance()->add_cyclic_timer(this->refresh_timer,
-        refresh_interval,
-        [this](uint64_t, uint64_t) {
-            // assert VBL interrupt
-            this->vbl_cb(1);
-            this->update_screen();
-        }
-    );
-
     if (vert_blank == 0) {
         LOG_F(ERROR, "Vertical blank is 0. Using 25 instead.");
         vert_blank = 25;
     }
 
     uint64_t vbl_duration = static_cast<uint64_t>((double)hori_total * vert_blank / this->pixel_clock * NS_PER_SEC + 0.5);
-    TimerManager::get_instance()-> add_cyclic_timer(this->vbl_end_timer,
+    TimerManager::get_instance()->add_cyclic_timer(
+        this->refresh_timer,
         refresh_interval,
-        refresh_interval + vbl_duration,
-        [this](uint64_t, uint64_t) {
-            // deassert VBL interrupt
-            this->vbl_cb(0);
+        [this, vbl_duration](uint64_t, uint64_t) {
+            this->vbl_cb(1); // assert VBL interrupt
+
+            if (this->vbl_end_timer.active) {
+                TimerManager::get_instance()->cancel_timer(this->vbl_end_timer);
+            }
+            TimerManager::get_instance()->add_oneshot_timer(
+                this->vbl_end_timer,
+                vbl_duration,
+                [this](uint64_t, uint64_t) {
+                    this->vbl_cb(0); // deassert VBL interrupt
+                }
+            );
+
+            this->update_screen();
         }
     );
 }