Add Sys_Tick example application

src/application/sys_tick/main.cc

@@ -0,0 +1,47 @@
+#include <array>
+
+extern "C" {
+    #include "nrf52.h"
+}
+
+#include "platform/nrf52/gpio.h"
+#include "platform/nrf52/InterruptHandler.h"
+#include "platform/nrf52/InterruptGuardian.h"
+#include "platform/cm4/SystemTick.h"
+
+using namespace pinetime::platform::nrf52;
+
+enum {
+    PIN_NUMBER_LED_1 = 17,
+    PIN_NUMBER_LED_2 = 18,
+    PIN_NUMBER_LED_3 = 19,
+    PIN_NUMBER_LED_4 = 20
+};
+
+Gpio led_1(PIN_NUMBER_LED_1);
+Gpio led_2(PIN_NUMBER_LED_2);
+Gpio led_3(PIN_NUMBER_LED_3);
+Gpio led_4(PIN_NUMBER_LED_4);
+
+std::array<Gpio *, 4> leds = {&led_1, &led_2, &led_3, &led_4};
+
+InterruptGuardian InterruptGuardian::instance;
+
+pinetime::platform::cm4::SystemTick ticker;
+
+int main(void)
+{
+    ticker.enable();
+    uint32_t last_tick = 0;
+    while(true) {
+        for(auto it = std::begin(leds); it != std::end(leds); ++it) {
+            uint32_t tick = ticker.tick() / 1000;
+            if(tick != last_tick) {
+                Gpio * tmp = *it;
+                tmp->toggle();
+                last_tick = tick;
+            }
+        }
+    }
+    return 0;
+}