Scheduler refactor Pt. 1

* Simplifies scheduling logic, specifically regarding thread status. It should be much clearer which statuses are valid
for a thread at any given point in the system.
* Removes dead code from thread.cpp.
* Moves the implementation of resetting a ThreadContext to the corresponding core's implementation.

Other changes:
* Fixed comments in arm interfaces.
* Updated comments in thread.cpp
* Removed confusing, useless, functions like MakeReady() and ChangeStatus() from thread.cpp.
* Removed stack_size from Thread. In the CTR kernel, the thread's stack would be allocated before thread creation.

src/core/arm/arm_interface.h

@@ -85,6 +85,15 @@ public:
      */
     virtual void AddTicks(u64 ticks) = 0;
 
+    /**
+     * Initializes a CPU context for use on this CPU
+     * @param context Thread context to reset
+     * @param stack_top Pointer to the top of the stack
+     * @param entry_point Entry point for execution
+     * @param arg User argument for thread
+     */
+    virtual void ResetContext(Core::ThreadContext& context, u32 stack_top, u32 entry_point, u32 arg) = 0;
+
     /**
      * Saves the current CPU context
      * @param ctx Thread context to save

src/core/arm/dyncom/arm_dyncom.cpp

@@ -93,6 +93,16 @@ void ARM_DynCom::ExecuteInstructions(int num_instructions) {
     AddTicks(ticks_executed);
 }
 
+void ARM_DynCom::ResetContext(Core::ThreadContext& context, u32 stack_top, u32 entry_point, u32 arg) {
+    memset(&context, 0, sizeof(Core::ThreadContext));
+
+    context.cpu_registers[0] = arg;
+    context.pc = entry_point;
+    context.sp = stack_top;
+    context.cpsr = 0x1F; // Usermode
+    context.mode = 8;    // Instructs dyncom CPU core to start execution as if it's "resuming" a thread.
+}
+
 void ARM_DynCom::SaveContext(Core::ThreadContext& ctx) {
     memcpy(ctx.cpu_registers, state->Reg, sizeof(ctx.cpu_registers));
     memcpy(ctx.fpu_registers, state->ExtReg, sizeof(ctx.fpu_registers));

src/core/arm/dyncom/arm_dyncom.h

@@ -13,79 +13,24 @@
 
 class ARM_DynCom final : virtual public ARM_Interface {
 public:
-
     ARM_DynCom();
     ~ARM_DynCom();
 
-    /**
-     * Set the Program Counter to an address
-     * @param pc Address to set PC to
-     */
     void SetPC(u32 pc) override;
-
-    /*
-     * Get the current Program Counter
-     * @return Returns current PC
-     */
     u32 GetPC() const override;
-
-    /**
-     * Get an ARM register
-     * @param index Register index (0-15)
-     * @return Returns the value in the register
-     */
     u32 GetReg(int index) const override;
-
-    /**
-     * Set an ARM register
-     * @param index Register index (0-15)
-     * @param value Value to set register to
-     */
     void SetReg(int index, u32 value) override;
-
-    /**
-     * Get the current CPSR register
-     * @return Returns the value of the CPSR register
-     */
     u32 GetCPSR() const override;
-
-    /**
-     * Set the current CPSR register
-     * @param cpsr Value to set CPSR to
-     */
     void SetCPSR(u32 cpsr) override;
 
-    /**
-     * Returns the number of clock ticks since the last reset
-     * @return Returns number of clock ticks
-     */
     u64 GetTicks() const override;
-
-    /**
-    * Advance the CPU core by the specified number of ticks (e.g. to simulate CPU execution time)
-    * @param ticks Number of ticks to advance the CPU core
-    */
     void AddTicks(u64 ticks) override;
 
-    /**
-     * Saves the current CPU context
-     * @param ctx Thread context to save
-     */
+    void ResetContext(Core::ThreadContext& context, u32 stack_top, u32 entry_point, u32 arg);
     void SaveContext(Core::ThreadContext& ctx) override;
-
-    /**
-     * Loads a CPU context
-     * @param ctx Thread context to load
-     */
     void LoadContext(const Core::ThreadContext& ctx) override;
 
-    /// Prepare core for thread reschedule (if needed to correctly handle state)
     void PrepareReschedule() override;
-
-    /**
-     * Executes the given number of instructions
-     * @param num_instructions Number of instructions to executes
-     */
     void ExecuteInstructions(int num_instructions) override;
 
 private: