The mbed ports used wrong time computations for the (#1642)

'jerry_port_get_current_time' function. Microseconds was used instead of
milliseconds.

A quick fix has been done in the Yotta-based mbed port, and an extended one
- with correction - works in the mbed OS 5 port now.

JerryScript-DCO-1.0-Signed-off-by: Gabor Loki loki@inf.u-szeged.hu

targets/mbed/source/port/jerry_port.c

@@ -76,10 +76,12 @@ jerry_port_get_time_zone (jerry_time_zone_t *tz_p) /**< timezone pointer */
 /**
  * Implementation of jerry_port_get_current_time.
  *
- * @return current timer's counter value in microseconds 
+ * @return current timer's counter value in milliseconds
  */
 double
 jerry_port_get_current_time (void)
 {
-  return (double) us_ticker_read ();
+  /* Note: if the target has its own RTC, this value should be extended by the
+   * RTC's one. */
+  return (double) us_ticker_read () / 1000;
 } /* jerry_port_get_current_time */

targets/mbedos5/source/jerry_port_mbed.c

@@ -90,10 +90,34 @@ jerry_port_get_time_zone (jerry_time_zone_t *tz_p) /**< timezone pointer */
 /**
  * Implementation of jerry_port_get_current_time.
  *
- * @return current timer's counter value in microseconds
+ * @return current timer's counter value in milliseconds
  */
 double
 jerry_port_get_current_time (void)
 {
-  return (double) us_ticker_read ();
+  static uint64_t last_tick = 0;
+  static time_t last_time = 0;
+  static uint32_t skew = 0;
+
+  uint64_t curr_tick = us_ticker_read (); /* The value is in microseconds. */
+  time_t curr_time = time(NULL); /*  The value is in seconds. */
+  double result = curr_time * 1000;
+
+  /* The us_ticker_read () has an overflow for each UINT_MAX microseconds
+   * (~71 mins). For each overflow event the ticker-based clock is about 33
+   * milliseconds fast. Without a timer thread the milliseconds part of the
+   * time can be corrected if the difference of two get_current_time calls
+   * are within the mentioned 71 mins. Above that interval we can assume
+   * that the milliseconds part of the time is negligibe.
+   */
+  if (curr_time - last_time > (time_t)(((uint32_t)-1) / 1000000)) {
+    skew = 0;
+  } else if (last_tick > curr_tick) {
+    skew = (skew + 33) % 1000;
+  }
+  result += (curr_tick / 1000 - skew) % 1000;
+
+  last_tick = curr_tick;
+  last_time = curr_time;
+  return result;
 } /* jerry_port_get_current_time */