esp8266: Fix ticks_ms to correctly handle wraparound of system counter.
Fixes issue #4795.
diff --git a/ports/esp8266/ets_alt_task.h b/ports/esp8266/ets_alt_task.h
index e7a15c3..7eb8ff3 100644
--- a/ports/esp8266/ets_alt_task.h
+++ b/ports/esp8266/ets_alt_task.h
@@ -3,8 +3,10 @@
extern int ets_loop_iter_disable;
extern int ets_loop_dont_feed_sw_wdt;
+extern uint32_t system_time_low_word;
extern uint32_t system_time_high_word;
+void system_time_update(void);
bool ets_loop_iter(void);
#endif // MICROPY_INCLUDED_ESP8266_ETS_ALT_TASK_H