Perform reset only when there is no work to be done

When the application schedules a reset, we need to postpone the reset
until the main loop (thread) has no more work to do to give ongoing
tasks, e.g., NVM update, a chance to finish. The main thread has no more
work to when the application has no sleep lock active.

Fixes a bug introduced by the fix for #53

src/main.c

@@ -50,7 +50,13 @@ int main(void)
         sysconf_process();
 
         CRITICAL_SECTION_BEGIN();
-        if (schedule_reset) system_reset();
+
+        // If the application scheduled a reset, perform it as soon as the MCU
+        // is allowed to sleep, which indicates that there is no more work to be
+        // done (e.g., NVM updates).
+        if (schedule_reset && system_sleep_allowed())
+            system_reset();
+
         else if (sysconf.sleep) system_low_power();
         CRITICAL_SECTION_END();
     }

src/system.c

@@ -105,6 +105,11 @@ unsigned system_get_stop_mode_mask(void)
     return mask;
 }
 
+int system_sleep_allowed(void)
+{
+    return sleep_mask == 0;
+}
+
 void system_allow_sleep(system_module_t module)
 {
     irq_disable();

src/system.h

@@ -45,6 +45,8 @@ bool system_is_stop_mode_allowed(void);
 
 unsigned system_get_stop_mode_mask(void);
 
+int system_sleep_allowed(void);
+
 void system_allow_sleep(system_module_t module);
 
 void system_disallow_sleep(system_module_t module);