diff --git a/src/cpu/mod.rs b/src/cpu/mod.rs
index d09bfdc..327650a 100644
--- a/src/cpu/mod.rs
+++ b/src/cpu/mod.rs
@@ -1,8 +1,8 @@
 use std::{cell::RefCell, rc::Rc};
-use crate::bus::*;
-use crate::ram;
+use crate::system::bus::*;
+use crate::system::ram;
+use crate::system::rv32;
 use crate::inst;
-use crate::rv32;
 
 // Register ABI         Description             Saver
 // x0       zero        Zero                    Immutable
diff --git a/src/ext/decode.rs b/src/ext/decode.rs
new file mode 100644
index 0000000..7b262f7
--- /dev/null
+++ b/src/ext/decode.rs
@@ -0,0 +1,36 @@
+use crate::system::rv32;
+use crate::cpu;
+
+macro_rules! match_mask {
+    ($int:expr, $($bit:expr)+) => { 'scope: {
+        let mut int = $int;
+
+        $({
+            let msb = int & (1 << 31);
+            let bit = $bit;
+            if (bit == 0 || bit == 1) && bit != msb.reverse_bits() {
+                break 'scope false;
+            }
+            int <<= 1;
+        })+
+
+        true
+    }};
+}
+
+trait Instruction {
+    fn get_mask() -> rv32::Word;
+    fn step(&self, inst: rv32::Word, state: &mut cpu::CPU);
+}
+
+struct ADDI {}
+impl Instruction for ADDI  {
+    fn get_mask() -> rv32::Word {
+    }
+}
+
+pub fn decode_inst(inst: rv32::WORD) -> fn() {
+    // loop over all bitmasks
+    // 
+
+}
diff --git a/src/ext/mod.rs b/src/ext/mod.rs
index c730e33..5331d4b 100644
--- a/src/ext/mod.rs
+++ b/src/ext/mod.rs
@@ -1 +1,12 @@
-use crate::
+use crate::system::rv32;
+
+mod decode;
+
+// Instruction bitmasks
+//      This will be awkward as the instruction types
+//      are sometimes shared accross modules (float / double)
+// Instruction parsing
+// Extensibility
+
+type Instruction = rv32::Word;
+
diff --git a/src/inst.rs b/src/inst.rs
index 22238b8..92de238 100644
--- a/src/inst.rs
+++ b/src/inst.rs
@@ -1,6 +1,6 @@
 use modular_bitfield::prelude::*;
 
-use crate::rv32;
+use crate::system::rv32;
 
 pub const R_TYPE: u8 = 0b00110011;
 pub const I_TYPE: u8 = 0b00010011;
diff --git a/src/main.rs b/src/main.rs
index 55b2599..3c3df4a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,13 +3,12 @@ use std::io::BufReader;
 use std::io::Read;
 use std::{cell::RefCell, rc::Rc};
 
-mod bus;
 mod cpu;
+mod ext;
+mod system;
 mod inst;
-mod ram;
-mod rv32;
 
-use crate::bus::*;
+use crate::system::bus;
 use crate::cpu::*;
 
 struct VMRV32I {
@@ -19,7 +18,7 @@ struct VMRV32I {
 
 impl VMRV32I {
     fn new() -> VMRV32I {
-        let bus = Rc::new(RefCell::new(Bus::new()));
+        let bus = Rc::new(RefCell::new(bus::Bus::new()));
         let mut cpu = CPU::new(Rc::clone(&bus));
         cpu.init();
         VMRV32I { cpu, bus }
diff --git a/src/bus.rs b/src/system/bus.rs
similarity index 98%
rename from src/bus.rs
rename to src/system/bus.rs
index 4cc8be6..198a058 100644
--- a/src/bus.rs
+++ b/src/system/bus.rs
@@ -1,7 +1,7 @@
 pub const DRAM_BASE: u32 = 0x80000000;
 
-use crate::rv32;
-use crate::ram;
+use crate::system::rv32;
+use crate::system::ram;
 
 pub struct Bus {
     memory: ram::RAM,
diff --git a/src/system/mod.rs b/src/system/mod.rs
new file mode 100644
index 0000000..5695648
--- /dev/null
+++ b/src/system/mod.rs
@@ -0,0 +1,3 @@
+pub mod bus;
+pub mod ram;
+pub mod rv32;
diff --git a/src/ram.rs b/src/system/ram.rs
similarity index 97%
rename from src/ram.rs
rename to src/system/ram.rs
index d9440af..da9b6c3 100644
--- a/src/ram.rs
+++ b/src/system/ram.rs
@@ -1,5 +1,5 @@
-use crate::bus;
-use crate::rv32;
+use crate::system::bus;
+use crate::system::rv32;
 
 //pub const DRAM_SIZE: u32 = 1 * 1024 * 1024 * 1024; // 1GB
 //pub const DRAM_SIZE: u32 = 1 * 1024; // 1KB
diff --git a/src/rv32.rs b/src/system/rv32.rs
similarity index 100%
rename from src/rv32.rs
rename to src/system/rv32.rs