Make sure the timer wraps around correctly independent of the os tick frequency

tmk_core/common/chibios/timer.c

@@ -2,26 +2,40 @@
 
 #include "timer.h"
 
-void timer_init(void) {}
+static systime_t last_systime = 0;
+static systime_t overflow = 0;
+static uint32_t current_time_ms = 0;
 
-void timer_clear(void) {}
+void timer_init(void) {
+  timer_clear();
+}
+
+void timer_clear(void) {
+  last_systime = chVTGetSystemTime();
+  overflow = 0;
+  current_time_ms = 0;
+}
 
-uint16_t timer_read(void)
-{
-    return (uint16_t)ST2MS(chVTGetSystemTime());
+uint16_t timer_read(void) {
+  return (uint16_t)timer_read32();
 }
 
-uint32_t timer_read32(void)
-{
-    return ST2MS(chVTGetSystemTime());
+uint32_t timer_read32(void) {
+  // Note: We assume that the timer update is called at least once betweeen every wrap around of the system time
+  systime_t current_systime = chVTGetSystemTime();
+  systime_t elapsed = current_systime - last_systime + overflow;
+  uint32_t elapsed_ms = ST2MS(elapsed);
+  current_time_ms += elapsed_ms;
+  overflow = elapsed - MS2ST(elapsed_ms);
+  last_systime = current_systime;
+
+  return current_time_ms;
 }
 
-uint16_t timer_elapsed(uint16_t last)
-{
-    return (uint16_t)(ST2MS(chVTTimeElapsedSinceX(MS2ST(last))));
+uint16_t timer_elapsed(uint16_t last) {
+  return timer_read() - last;
 }
 
-uint32_t timer_elapsed32(uint32_t last)
-{
-    return ST2MS(chVTTimeElapsedSinceX(MS2ST(last)));
+uint32_t timer_elapsed32(uint32_t last) {
+  return timer_read32() - last;
 }