Cache signals during each kernel tick to make run order more predictable

Kernel.cpp

@@ -30,7 +30,7 @@ void Kernel_setup()
   last_tick_duration = 0;
 }
 
-void Kernel_start(int (*callback)(int, unsigned int), unsigned long interval)
+int Kernel_start(int (*callback)(int, unsigned int), unsigned long interval)
 {
   struct Task *process = Kernel_get_task(0);
   if (process->pid == -1)
@@ -44,6 +44,8 @@ void Kernel_start(int (*callback)(int, unsigned int), unsigned long interval)
   process->run_accumulator = interval;
   process->signal = SIGNAL_START | SIGNAL_TICK;
   process->running = true;
+
+  return process->pid;
 }
 
 void Kernel_enable(int pid)
@@ -86,7 +88,7 @@ void Kernel_signal(unsigned int signal)
   {
     if (tasks[i].pid != 0 && tasks[i].running == true)
     {
-      tasks[i].signal |= signal;
+      tasks[i].signal_pending |= signal;
     }
   }
 }
@@ -96,7 +98,7 @@ void Kernel_signal(int pid, unsigned int signal)
   struct Task *process = Kernel_get_task(pid);
   if (process->pid == pid)
   {
-    process->signal |= signal;
+    process->signal_pending |= signal;
   }
 }
 
@@ -188,7 +190,7 @@ void Kernel_tick()
   unsigned long next_tick_due = ULONG_MAX;
   int running_tasks = 0;
   int last_exit_code = 0;
-  
+
   for (int i=0; i<MAX_TASKS; i++)
   {
     // If the task is initialized (non-zero PID) and is marked as running
@@ -222,14 +224,9 @@ void Kernel_tick()
       // If the process has any non-masked signals pending, run it
       if ((tasks[i].signal & tasks[i].signal_mask) != 0)
       {
-
-        unsigned int signals = tasks[i].signal;
-        tasks[i].signal = SIGNAL_NONE;
-        
         // Run the task
-        int task_return = (*tasks[i].callback)(tasks[i].pid, signals);
+        int task_return = (*tasks[i].callback)(tasks[i].pid, tasks[i].signal);
         
-
         // If the tasks's return value was non-zero, it has exited.
         if (task_return != 0)
         {
@@ -242,7 +239,6 @@ void Kernel_tick()
           last_exit_code = task_return;
         }
       }
-      
 
       // Check each task to see if it's the one scheduled to run on the next closest tick, and track it
       // so we can put the processor to sleep until then.
@@ -260,16 +256,19 @@ void Kernel_tick()
     Kernel_panic(panic_msg);
   }
 
-  // If no signals pending, put processor to sleep until the next scheduled run of a task
-  // Leave the home button enabled to force a wake-up before then
   bool signals_pending = false;
   for (int i=0; i<MAX_TASKS; i++)
   {
+    tasks[i].signal = tasks[i].signal_pending;
+    tasks[i].signal_pending = SIGNAL_NONE;
+    
     if ((tasks[i].signal & tasks[i].signal_mask) != 0)
     {
       signals_pending = true;
     }
   }
+  
+  // If no signals pending, put processor to sleep until the next scheduled run of a task
   if (!signals_pending)
   {
     esp_sleep_enable_timer_wakeup(next_tick_due * 1000);

Kernel.h

@@ -8,6 +8,7 @@ struct Task
   unsigned long run_interval = 0;
   unsigned long run_accumulator = 0;
   unsigned int signal = 0;
+  unsigned int signal_pending = 0;
   unsigned int signal_mask = 0xFFFF;
 };
 
@@ -18,7 +19,7 @@ void Kernel_tick();
 void Kernel_panic(char* message);
 
 // Start a new process
-void Kernel_start(int (*callback)(int, unsigned int), unsigned long interval);
+int Kernel_start(int (*callback)(int, unsigned int), unsigned long interval);
 // Continue execution of a process
 void Kernel_enable(int pid);
 // Pause execution of a process