1 files changed, 51 insertions, 0 deletions
diff --git a/src/isa.ads b/src/isa.ads
new file mode 100644
index 0000000..656fcbf
--- /dev/null
+++ b/src/isa.ads
@@ -0,0 +1,51 @@
+package ISA is
+   type Byte           is mod 2 ** 8;
+   type Address        is mod 2 ** 12;
+   type Register_Index is mod 2 ** 4;
+   type Bank           is array (Address) of Byte;
+   type Register_Bank  is array (Register_Index) of Byte;
+   type Pixel          is array (0 .. 7) of Boolean;
+   pragma Pack (Pixel);
+
+   type Opcode_Value is mod 2 ** 12;
+   type Opcode_Class is (
+      Flow, Jump, Call, Equal, Not_Equal, Compare, Set_Register, Add, Math,
+      Not_Compare, Set_Address, Jump_Relative, Random, Draw_Sprite, Input, Misc
+   ) with Size => 4;
+   type Opcode_Raw   is mod 2 ** 16;
+   type Opcode is record
+      Value : Opcode_Value;
+      Class : Opcode_Class;
+   end record with
+      Size => 16;
+
+   for Opcode use record
+      Value at 0 range 0 .. 11;
+      Class at 0 range 12 .. 15;
+   end record;
+
+   for Opcode_Class use (
+      Flow          => 0,
+      Jump          => 1,
+      Call          => 2,
+      Equal         => 3,
+      Not_Equal     => 4,
+      Compare       => 5,
+      Set_Register  => 6,
+      Add           => 7,
+      Math          => 8,
+      Not_Compare   => 9,
+      Set_Address   => 10,
+      Jump_Relative => 11,
+      Random        => 12,
+      Draw_Sprite   => 13,
+      Input         => 14,
+      Misc          => 15);
+
+   Start_Address : constant Address := 16#200#;
+
+   function To_Byte (O : Opcode) return Byte;
+
+   function X_Register (O : Opcode) return Register_Index;
+   function Y_Register (O : Opcode) return Register_Index;
+end ISA;