py/scheduler: Add optional port hook for when something is scheduled.

So that a port can "wake up" when there is work to do.

Signed-off-by: Damien George <damien@micropython.org>

py/mpconfig.h

@@ -550,6 +550,12 @@
 #define MICROPY_VM_HOOK_RETURN
 #endif
 
+// Hook for mp_sched_schedule when a function gets scheduled on sched_queue
+// (this macro executes within an atomic section)
+#ifndef MICROPY_SCHED_HOOK_SCHEDULED
+#define MICROPY_SCHED_HOOK_SCHEDULED
+#endif
+
 // Whether to include the garbage collector
 #ifndef MICROPY_ENABLE_GC
 #define MICROPY_ENABLE_GC (0)

py/scheduler.c

@@ -134,6 +134,7 @@ bool MICROPY_WRAP_MP_SCHED_SCHEDULE(mp_sched_schedule)(mp_obj_t function, mp_obj
         uint8_t iput = IDX_MASK(MP_STATE_VM(sched_idx) + MP_STATE_VM(sched_len)++);
         MP_STATE_VM(sched_queue)[iput].func = function;
         MP_STATE_VM(sched_queue)[iput].arg = arg;
+        MICROPY_SCHED_HOOK_SCHEDULED;
         ret = true;
     } else {
         // schedule queue is full