esp8266: Fix ticks_ms to correctly handle wraparound of system counter.

Fixes issue #4795.

1 files changed, 14 insertions, 9 deletions

diff --git a/ports/esp8266/ets_alt_task.c b/ports/esp8266/ets_alt_task.c
index b724b8f14..0b1615d65 100644
--- a/ports/esp8266/ets_alt_task.c
+++ b/ports/esp8266/ets_alt_task.c
@@ -112,22 +112,27 @@ int ets_loop_iter_disable = 0;
 int ets_loop_dont_feed_sw_wdt = 0;
 
 // to implement a 64-bit wide microsecond counter
-static uint32_t system_time_prev = 0;
+uint32_t system_time_low_word = 0;
 uint32_t system_time_high_word = 0;
 
-bool ets_loop_iter(void) {
-    if (ets_loop_iter_disable) {
-        return false;
-    }
-
-    // handle overflow of system microsecond counter
+void system_time_update(void) {
+    // Handle overflow of system microsecond counter
     ets_intr_lock();
     uint32_t system_time_cur = system_get_time();
-    if (system_time_cur < system_time_prev) {
+    if (system_time_cur < system_time_low_word) {
         system_time_high_word += 1; // record overflow of low 32-bits
     }
-    system_time_prev = system_time_cur;
+    system_time_low_word = system_time_cur;
     ets_intr_unlock();
+}
+
+bool ets_loop_iter(void) {
+    if (ets_loop_iter_disable) {
+        return false;
+    }
+
+    // Update 64-bit microsecond counter
+    system_time_update();
 
     // 6 words before pend_flag_noise_check is a variable that is used by
     // the software WDT.  A 1.6 second period timer will increment this