fix the represntation of at_the_end_of_time to be 63 one bits rather than 32

src/common/pico_time/include/pico/time.h

@@ -155,7 +155,9 @@ static inline int64_t absolute_time_diff_us(absolute_time_t from, absolute_time_
     return (int64_t)(to_us_since_boot(to) - to_us_since_boot(from));
 }
 
-/*! \brief The timestamp representing the end of time; no timestamp is after this
+/*! \brief The timestamp representing the end of time; this is actually not the maximum possible
+ * timestamp, but is set to 0x7fffffff_ffffffff microseconds to avoid sign overflows with time
+ * arithmetic. This is still over 7 million years, so should be sufficient.
  * \ingroup timestamp
  */
 extern const absolute_time_t at_the_end_of_time;

src/common/pico_time/time.c

@@ -11,10 +11,9 @@
 #include "pico/time.h"
 #include "pico/util/pheap.h"
 #include "hardware/sync.h"
-#include "hardware/gpio.h"
 
 const absolute_time_t ABSOLUTE_TIME_INITIALIZED_VAR(nil_time, 0);
-const absolute_time_t ABSOLUTE_TIME_INITIALIZED_VAR(at_the_end_of_time, ULONG_MAX);
+const absolute_time_t ABSOLUTE_TIME_INITIALIZED_VAR(at_the_end_of_time, INT64_MAX);
 
 typedef struct alarm_pool_entry {
     absolute_time_t target;