how is APP_timer running? like a thread?

Question

hi, i was just wondering whether the app_timer works like a function or like a thread. 
 e.g. lets say i got my mainloop 
 while(1)
{
start_timer(...);
//DO SOMETHING
} 
 and my timer function 
 void dummy_timer_handler(...)
{
//DO SOMETHING ELSE
} 
 when the timer expires and the handler function is called, is my main loop paused? or does it run in parallel?

Nathan · Accepted Answer

It is interrupt based. By default, as soon as the timer expires, the main loop pauses on the next instruction and the handler is run. When the handler returns, the main loop resumes where it left off. 
 If you want it to behave more like a thread where you tell an OS when it is safe to run the handler, you can somewhat fake it by using the APP scheduler version of APP timer (also in the Nordic SDK). The main loop will still pause momentarily at timeout, but it just sends a message to the scheduler that you want the timeout function to be run later. It will run the next time you call the app_sched_execute() function. This requires you to build app_timer_appsh.c and app_scheduler.c. Both of their header files will need to be included, and you will have to initialize the scheduler and tell the app timer that you want it to use the scheduler. Quick example code (not guaranteed to work as is, but should be close) (I recommend making max buffered messages at least OP_QUEUE_SIZE or larger, and making max scheduler message size needs to be at minimum sizeof(app_timer_event_t)): 
 #include <stdint.h>
#include "app_scheduler.h"
#include "app_timer.h"
#include "app_timer_appsh.h"

#define OP_QUEUE_SIZE 6

void main(void)
{
 static uint32_t APP_TIMER_BUF[CEIL_DIV(APP_TIMER_BUF_SIZE(OP_QUEUE_SIZE),
 sizeof(uint32_t))];
 APP_SCHED_INIT(/*Insert max scheduler message size here*/, /*Insert max buffered messages here*/);
 (void)app_timer_init((APP_TIMER_PRESCALER), OP_QUEUE_SIZE, APP_TIMER_BUF, app_timer_evt_schedule);
 
 // Add app timer create here, no different from normal
 
 while(1) {
 app_sched_execute(); // Timer timeout handler functions called here, when appropriate
 
 /* Do stuff here */
 /* Start timer on conditions whenever in here */
 }
}

how is APP_timer running? like a thread?

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