From 033f63ec4209490c634893aa5625528f2c2c7a30 Mon Sep 17 00:00:00 2001
From: Fabien Freling <public@ffreling.com>
Date: Mon, 29 Feb 2016 23:07:42 +0100
Subject: [PATCH] Add interrupt handlers in cpu

---
 src/cpu.ml       | 66 ++++++++++++++++++++++++++++++++++++++++++++----
 src/interrupt.ml | 15 ++++++-----
 2 files changed, 69 insertions(+), 12 deletions(-)

diff --git a/src/cpu.ml b/src/cpu.ml
index 4215bf1..a860504 100644
--- a/src/cpu.ml
+++ b/src/cpu.ml
@@ -130,6 +130,11 @@ let read_pc_2bytes cpu mem =
   inc_pc cpu 2;
   word
 
+(*************************************************
+ *
+ *  Stack manipulation
+ *
+ ************************************************)
 let pop_stack cpu mem =
   let low = Memory.get mem cpu.reg.sp in
   cpu.reg.sp <- (cpu.reg.sp + 1) mod 0xFFFF;
@@ -137,11 +142,23 @@ let pop_stack cpu mem =
   cpu.reg.sp <- (cpu.reg.sp + 1) mod 0xFFFF;
   merge_bytes low high
 
+let push_pc_stack cpu mem =
+  let (high, low) = split_2B cpu.reg.pc in
+  cpu.reg.sp <- pred cpu.reg.sp;
+  Memory.set mem cpu.reg.sp high;
+  cpu.reg.sp <- pred cpu.reg.sp;
+  Memory.set mem cpu.reg.sp low
 
-(**
-  http://imrannazar.com/GameBoy-Z80-Opcode-Map
-  https://github.com/sinamas/gambatte/blob/master/libgambatte/src/cpu.cpp
-*)
+
+
+
+(*************************************************
+ *
+ *  CPU instructions
+ *
+ ************************************************)
+(** http://imrannazar.com/GameBoy-Z80-Opcode-Map
+    https://github.com/sinamas/gambatte/blob/master/libgambatte/src/cpu.cpp *)
 let run cpu (mem: Memory.map) =
   print_cpu_state cpu;
   let opcode = read_pc_byte cpu mem |> char_of_int in
@@ -294,7 +311,8 @@ let run cpu (mem: Memory.map) =
               inst, 8
 
   | '\xFB' -> let inst = sprintf "EI" in
-              (* enable interrupts, IME=1 *)
+              (* enable interrupts *)
+              Interrupt.ime := true;
               inst, 4
 
   |  x -> eprintf "opcode 0x%02X\n" (int_of_char x);
@@ -304,3 +322,41 @@ let run cpu (mem: Memory.map) =
   in
   inc_cycles cpu cycles;
   inst, cycles
+
+
+(*************************************************
+ *
+ *  Interrupt handlers
+ *
+ ************************************************)
+let handle_interrupt cpu mem flag =
+  let int_vector = match flag with
+  | Interrupt.V_Blank  -> 0x40
+  | Interrupt.LCD_Stat -> 0x48
+  | Interrupt.Timer    -> 0x50
+  | Interrupt.Serial   -> 0x58
+  | Interrupt.Joypad   -> 0x60 in
+
+  (* TODO: reset IF flag *)
+  Interrupt.ime := false;
+
+  push_pc_stack cpu mem;
+  cpu.reg.pc <- int_vector
+
+  (* TODO: run cpu until RETI is called *)
+
+
+
+let handle_interrupts cpu mem ie if_ =
+  if not !Interrupt.ime then 
+    () (* Interrupt Master Enable flag set to false, nothing to do *)
+  else
+  begin
+    (* N.B.: flags are precomputed once but an interrupt could be requested
+       during that time *)
+    let interrupts = ie land if_ in
+    let flags = Interrupt.get_flags interrupts in
+    match flags with
+    | [] -> () (* No interrupt *)
+    | _ -> List.iter (fun x -> handle_interrupt cpu mem x) flags
+  end
diff --git a/src/interrupt.ml b/src/interrupt.ml
index b175557..3e28847 100644
--- a/src/interrupt.ml
+++ b/src/interrupt.ml
@@ -6,15 +6,16 @@
  * LICENSE file at the top level directory of this source tree.
  *)
 
-(* let IME = ref false;; *)
+let ime = ref false;;
 
 type t =
-  |  V_Blank
-  |  LCD_Stat
-  |  Timer
-  |  Serial
-  |  Joypad
+  | V_Blank
+  | LCD_Stat
+  | Timer
+  | Serial
+  | Joypad
 
+(** Return the list of interrupt flags sorted by priority. *)
 let get_flags byte =
 
   let nth_interrupt i =
@@ -34,6 +35,6 @@ let get_flags byte =
         get_flag byte (i + 1) (interrupt :: accu)
       else
         get_flag byte (i + 1) accu
-    | _ -> accu in
+    | _ -> List.rev accu in
 
   get_flag byte 0 []