wip

src/core/memory.ml

@@ -94,7 +94,6 @@ let inc mem addr =
   Bytes.set m x c;
   overflow
 
-
 let update_timers mem cycles =
   let should_inc_div = Timer.update mem.timer_div cycles in
   if should_inc_div then ignore (inc mem.map gDIV);
@@ -109,13 +108,26 @@ let update_timers mem cycles =
     end
   end
 
+(* A tile is 8x8, with each pixel encoded in 2 bits:
+ * - the whole tile takes 16 bytes
+ * - each line takes 2 bytes
+ *   - the first byte contains the least significant bit for the row
+ *   - the second byte contains the upper bit
+ *   - 8th bit is the leftmost
+ *   - 1st bit is the rigthmost *)
 let background_map mem n =
   let bg_map = Array2.create Bigarray.int8_unsigned Bigarray.c_layout 8 8 in
+  let offset = match n with
+  | 0 -> 0x1800 (* VRAM starts at 0x8000 *)
+  | 1 -> 0x1C00
+  | _ -> failwith "Invalid background map index" in
   Array2.fill bg_map 0;
   for j = 0 to (Array2.dim2 bg_map) - 1 do
     for i = 0 to (Array2.dim1 bg_map) - 1 do
       (* bg_map.{i, j} <- (i + j * Array2.dim1 bg_map) mod 4 *)
-      bg_map.{i, j} <- n
+      let mem_addr = i + j * Array2.dim1 bg_map in
+      let tile_index = Bytes.get mem.map.vram mem_addr |> int_of_char in
+      bg_map.{i, j} <- tile_index mod 4
     done
   done;
   bg_map