Fix timer Agptek Rocker (other hosted players)

on timer_unregister callbacks are not removed

It seems (at least on the Rocker) timers continue to fire (for a bit??)

Now we store the registered callback in the sigev structure and check
that the callback matches the one registered when the timer is created.

This should stop the possible case of a new timer getting spurious callbacks
We also now NULL the callbacks on un-register which should stop the segfaults

Added some notes to timer.c and timer.h

Change-Id: Ia155c3a4e4af89f474d55ed845560ccc1fab85aa

1 files changed, 4 insertions, 0 deletions

diff --git a/firmware/timer.c b/firmware/timer.c
index a923290a94..c618f72e02 100644
--- a/firmware/timer.c
+++ b/firmware/timer.c
@@ -42,6 +42,7 @@ bool timer_register(int reg_prio, void (*unregister_callback)(void),
         return false;
 
     pfn_timer = timer_callback;
+    /* NOTE: if unreg cb is defined you are in charge of calling timer_unregister() */
     pfn_unregister = unregister_callback;
     timer_prio = reg_prio;
 
@@ -53,6 +54,9 @@ bool timer_set_period(long cycles)
     return timer_set(cycles, false);
 }
 
+/* NOTE: unregister callbacks are not called by timer_unregister()
+* the unregister_callback only gets called when your timer gets 
+* overwritten by a lower priority timer using timer_register() */
 void timer_unregister(void)
 {
     timer_stop();