app_scheduler and app_timer

[Rob Philip]

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 

[Rob Philip]

Well I have a beginning of an understanding. nrf_serial_read uses app_timer and so *it* is not timing out and returning to me.

I basically stole my UART code from the SDK, and for its "sleep_function" it really was putting the processor to sleep, 

By telling it to wait for an interrupt of any sort, and then running the app_scheduler things seem to be working. 

I'm unsure if this is a "good" way to solve the problem, though.

Perhaps an alternate solution would be to use one of the hardware timers and have it run call app_sched_execute() on a periodic basis. Every 100 milliseconds or so. None of my app_timer events need to be services more often than every 250 milliseconds. But no - that won't work because the hardware timer callback is in ISR space rather than userland. For now, leaving the __SWI(); and app_sched_execute together in the sleep function of the nrf_serial abstraction will work for me, and I'll need to find a way to insert app_sched_execute into any other long-ish loops I end up running when I (today) start using the softdevice for BLE. 

Or is there a "better" way to do this? 

Below is my change to the sleep handler to support app_scheduler

uint32_t sleep_handler_count = 0;

static void sleep_handler(void)
{
   sleep_handler_count++;

#ifdef _USE_EXAMPLE_SLEEP_HANDLER_
   /*
   ** this shuts things down by allowing the processor to go into
   ** low power mode.
   */
   __WFE();
   __SEV();
   __WFE();
#else
   /*
   ** wait for an interrupt of any sort, and
   ** run the app_scheduler
   */
   __WFI();
   app_sched_execute();
#endif
}