RP2040: us_ticker: fix missing interrupts after 32bit wrap

Author: giulcioffi

targets/TARGET_RASPBERRYPI/TARGET_RP2040/us_ticker.c

@@ -53,11 +53,18 @@ const ticker_info_t* us_ticker_get_info()
     return &info;
 }
 
-const uint8_t alarm_num = 0;
+static const uint8_t alarm_num = 0;
+
+static void us_ticker_irq_handler_internal(uint alarm_src) {
+    if (alarm_num == alarm_src) {
+        us_ticker_irq_handler();
+    }
+}
 
 void us_ticker_init(void)
 {
-    hardware_alarm_set_callback(alarm_num, us_ticker_irq_handler);
+    hardware_alarm_claim(alarm_num);
+    hardware_alarm_set_callback(alarm_num, us_ticker_irq_handler_internal);
 }
 
 uint32_t us_ticker_read()
@@ -68,8 +75,25 @@ uint32_t us_ticker_read()
 void us_ticker_set_interrupt(timestamp_t timestamp)
 {
     core_util_critical_section_enter();
-    absolute_time_t target = {timestamp};
+
+    uint64_t _timestamp = (uint64_t)timestamp;
+
+    if (timestamp < time_us_32()) {
+        //32 bit timestamp has been wrapped
+        //We need to provide a 64 bit timestamp able to fire the irq for this round
+        _timestamp = (((time_us_64() >> 32) + 1) << 32) + timestamp;
+    } else {
+        //Then, at the next round, wrap the 64 bit timer to follow the 32 bit one
+        if ((time_us_64() >> 32) > 0) {
+            uint64_t current_time = time_us_64();
+            uint64_t wrapped_time = current_time - 0xFFFFFFFF;
+            timer_hw->timelw = (uint32_t)wrapped_time;
+            timer_hw->timehw = 0;
+        }
+    }
+    absolute_time_t target = { _timestamp };
     hardware_alarm_set_target(alarm_num, target);
+
     core_util_critical_section_exit();
 }
 
@@ -90,4 +114,5 @@ void us_ticker_clear_interrupt(void)
 
 void us_ticker_free(void)
 {
+    hardware_alarm_unclaim(alarm_num);
 }