$SYS updates are now aligned to `sys_interval` seconds.

This means that if set to 10, for example, updates will be sent at times
matching x0 seconds. Previously update intervals were aligned to the
time the broker was started.

ChangeLog.txt

@@ -65,6 +65,9 @@ Broker:
   preferred websockets implementation.
 - Add support for X-Forwarded-For header for built in websockets.
 - Report persistence stats when starting.
+- $SYS updates are now aligned to `sys_interval` seconds, meaning that if set
+  to 10, for example, updates will be sent at times matching x0 seconds.
+  Previously update intervals were aligned to the time the broker was started.
 
 Plugins / plugin interface:
 - Add persist-sqlite plugin.

src/sys_tree.c

@@ -226,9 +226,10 @@ void sys_tree__update(void)
 	uint32_t len;
 	bool initial_publish;
 	time_t next_event;
+	static time_t last_update_real = 0;
 
 	if(db.config->sys_interval){
-		next_event = last_update - db.now_s + db.config->sys_interval;
+		next_event = db.config->sys_interval - db.now_real_s % db.config->sys_interval - 1;
 		if(next_event <= 0){
 			next_event = db.config->sys_interval;
 		}
@@ -236,7 +237,7 @@ void sys_tree__update(void)
 	}
 
 	if(db.config->sys_interval
-			&& db.now_s - db.config->sys_interval >= last_update){
+			&& db.now_real_s % db.config->sys_interval == 0 && last_update_real != db.now_real_s){
 
 		uptime = db.now_s - start_time;
 		len = (uint32_t)snprintf(buf, BUFLEN, "%" PRIu64 " seconds", (uint64_t)uptime);
@@ -408,6 +409,7 @@ void sys_tree__update(void)
 		}
 
 		last_update = db.now_s;
+		last_update_real = db.now_real_s;
 	}
 }