app_scheduler and app_timer

Question

I've searched and the majority of answers seem to be years old. 
 I have an existing app_timer event handler that works perfectly, blinking LEDs. 
 I will soon have another that needs to do some I/O and thus needs not to be running out of an ISR. 
 I enabled APP_SCHEDULER_ENABLED and APP_TIMER_CONFIG_USE_SCHEDULER 
 I put the following code into my "init" 
 
 #define SCHED_QUEUE_SIZE 16 
 #define SCHED_MAX_EVENT_DATA_SIZE 192

APP_SCHED_INIT(APP_TIMER_SCHED_EVENT_DATA_SIZE, SCHED_QUEUE_SIZE);

ret = app_timer_init ();
 APP_ERROR_CHECK (ret); and in my "main loop" I put this to make sure that things got called every 50 milliseconds or so. 
 
 do 
 { 
 /* 
 ** read from the input stream. 
 */ 
 serial_ret_code = nrf_serial_read (&serial0_uart, &c, 1 , NULL , 50 );
 if (NRF_SUCCESS != serial_ret_code)
 { 
 app_sched_execute();

continue ;
 } 
 else 
 { 
 app_sched_execute();

break ;
 }

} while ( true );



A couple of things happen. 

First, the event handler never gets called (again, this works fine without the app_scheduler) and second I get this in my debugger:


Stopped by vector catch

In the Call Stack window it shows me at address 0x8C4 - somewhere in the softdevice

MartinBL · Accepted Answer

I might be missing something here, but that first while(true) loop doesn't make sense to me. The point of the scheduler is to schedule operations to be run in the main context. So it would make more sense to do something like: 
 some_isr()
{
	... 
	app_sched_event_put(..., ..., read_serial)
}

main_while_loop()
{
	app_sched_execute();
	__WFE();
	__SEV();
	__WFE();
} 
 
 Furthermore, if you run the app_timer library using the scheduler, then the app_timer's event handlers are already scheduled and executed from the main context. Hence, there is no need to schedule even more things from within these timer handlers. 
 
 What I'd *really* like is some way to have app_sched_execute() run periodically... If you use 
 main_while_loop()
{
	app_sched_execute();
	whatever_go_to_sleep_method_you_want();
} 
 then app_sched_execute() will be called whenever it is necessary. No more, no less. It gets called whenever any interrupt occurs, but if the scheduler's queue is empty it returns immediately. If the system is sleeping while waiting for some serial input for example, it will wake up when the serial data is ready, then you queue whatever code you want to run in the main context from within the serial ISR, then the system exits the ISR, then the code returns to main context and executes all the queued code with app_sched_execute(). There is no need to call it periodically to make sure the queue is empty since all the scheduled code is executed immediately anyway.

app_scheduler and app_timer

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