App_timer stops working

[Nate]

I have a timer that is coming every 100ms. I use it as a system clock to time and manage events. The main function has a loop that calls sd_app_evt_wait() When woken up by the interrupt it reads an accelerometer through i2c.

It works for a while and then it stops working. What would cause the timer to stop working? I even changed the code to stop the timer, do the accelerometer read and then start the timer again and it still gets to a point where the timer stops firing.

//setting up timer APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_MAX_TIMERS, APP_TIMER_OP_QUEUE_SIZE, false);

err_code = app_timer_create(&m_timer_systemTick_id,APP_TIMER_MODE_REPEATED,systemTick);

//command to start timer app_timer_start(m_timer_systemTick_id,APP_TIMER_TICKS(100,APP_TIMER_PRESCALER),NULL);

[Dave_couling]

Does your app_timer use the scheduler or not?

Add app_sched_execute(); in your main loop to assure that scheduled events are executed

[Susheel Nuguru]

nothing looks wrong in your timer code. Like Dave_couling pointed out, use this along with scheduler. There will be many examples in SDK, search for APP_TIMER_APPSH_INIT

[Nate]

Is there a good place to read about how the scheduler works and examples? Thanks

[Dave_couling]

How the scheduler works isn't entirely clear in the documentation. I'll try my best to explain. With all MCU's there is the main loop and there are interrupts. Interrupts can be trigger from various sources, and depending on the source will have different priority for execution. Also as you know an interrupt is a blocking operation, blocking whatever code was executing, to run the ISR.

The scheduler allows your application to issue an event using app_sched_event_put. What this does is in the main loop if there are not Interrupts being handled and the system is idle it will execute any scheduler events via app_sched_execute(). If there any multiple pending scheduler events, they are processes in the order they are received (FIFO).

[Dave_couling]

Again a scheduler event is issued via app_sched_event_put:

app_sched_event_put(void * p_event_data, uint16_t event_size, app_sched_event_handler_t handler)

The handler parameter passed is a function, whose code is run when this event is executed.

The nice thing about using the scheduler with app_timers is that the app timeout handler is automatically used as the event handler. So if you initialize your APP_TIMER as using the scheduler, the timeout handler function will be handled as mentioned above. This is the safest order of execute for app_timers.

I am using SDK 6.1, as Aryan mentioned SDK 8.0 sets up the app_timers and scheduler slightly differently but the general concept of usage and execution is pretty much the same.