diff --git a/src/cpus/m68k/tests.rs b/src/cpus/m68k/tests.rs
index 0219a00..dae067d 100644
--- a/src/cpus/m68k/tests.rs
+++ b/src/cpus/m68k/tests.rs
@@ -703,8 +703,8 @@ mod execute_tests {
             ins: Instruction::MOVEA(Target::DirectDReg(0), 0, Size::Long),
             data: &[ 0x2040 ],
             cputype: M68kType::MC68010,
-            init: TestState { pc: 0x00000000, msp: 0x00000000, usp: 0x00000000, d0: 0xFEDCBA98, d1: 0x00000000, a0: 0x00000000, a1: 0x00000000, sr: 0x2700 },
-            fini: TestState { pc: 0x00000002, msp: 0x00000000, usp: 0x00000000, d0: 0xFEDCBA98, d1: 0x00000000, a0: 0xFEDCBA98, a1: 0x00000000, sr: 0x2700 },
+            init: TestState { pc: 0x00000000, msp: 0x00000000, usp: 0x00000000, d0: 0xFEDCBA98, d1: 0x00000000, a0: 0x00000000, a1: 0x00000000, sr: 0x27FF },
+            fini: TestState { pc: 0x00000002, msp: 0x00000000, usp: 0x00000000, d0: 0xFEDCBA98, d1: 0x00000000, a0: 0xFEDCBA98, a1: 0x00000000, sr: 0x27FF },
         },
         TestCase {
             name: "neg",
diff --git a/src/host/traits.rs b/src/host/traits.rs
index f7144fa..8a83868 100644
--- a/src/host/traits.rs
+++ b/src/host/traits.rs
@@ -1,4 +1,6 @@
 
+use std::sync::{Arc, Mutex, MutexGuard};
+
 use crate::error::Error;
 use crate::host::keys::Key;
 
@@ -43,3 +45,26 @@ pub trait BlitableSurface {
 }
 
 
+#[derive(Clone, Debug)]
+pub struct SharedData<T>(Arc<Mutex<T>>);
+
+impl<T> SharedData<T> {
+    pub fn new(init: T) -> SharedData<T> {
+        SharedData(Arc::new(Mutex::new(init)))
+    }
+
+    pub fn lock(&self) -> MutexGuard<'_, T> {
+        self.0.lock().unwrap()
+    }
+}
+
+impl<T: Copy> SharedData<T> {
+    pub fn set(&mut self, value: T) {
+        *(self.0.lock().unwrap()) = value;
+    }
+
+    pub fn get(&mut self) -> T {
+        *(self.0.lock().unwrap())
+    }
+}
+
diff --git a/src/memory.rs b/src/memory.rs
index 00aad05..6349232 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -130,13 +130,8 @@ impl Bus {
 
     pub fn insert(&mut self, base: Address, length: usize, dev: TransmutableBox) {
         let block = Block { base, length, dev };
-        for i in 0..self.blocks.len() {
-            if self.blocks[i].base > block.base {
-                self.blocks.insert(i, block);
-                return;
-            }
-        }
-        self.blocks.insert(0, block);
+        let i = self.blocks.iter().position(|cur| cur.base > block.base).unwrap_or(0);
+        self.blocks.insert(i, block);
     }
 
     pub fn get_device_at(&self, addr: Address, count: usize) -> Result<(TransmutableBox, Address), Error> {
diff --git a/src/peripherals/genesis/controllers.rs b/src/peripherals/genesis/controllers.rs
index e160c04..7c76520 100644
--- a/src/peripherals/genesis/controllers.rs
+++ b/src/peripherals/genesis/controllers.rs
@@ -1,8 +1,7 @@
 
 use crate::error::Error;
-use crate::signals::SyncSignal;
 use crate::devices::{Address, Addressable, Transmutable};
-use crate::host::traits::{Host, JoystickDevice, JoystickUpdater};
+use crate::host::traits::{Host, JoystickDevice, JoystickUpdater, SharedData};
 
 
 const REG_VERSION: Address      = 0x01;
@@ -23,7 +22,7 @@ pub struct GenesisControllerPort {
     /// Data contains bits:
     /// 11 | 10 | 9 |    8 |     7 | 6 | 5 | 4 |     3 |    2 |    1 |  0
     ///  X |  Y | Z | MODE | START | A | B | C | RIGHT | LEFT | DOWN | UP
-    pub data: SyncSignal<u16>,
+    pub data: SharedData<u16>,
 
     pub ctrl: u8,
     pub th_count: u8,
@@ -35,7 +34,7 @@ pub struct GenesisControllerPort {
 impl GenesisControllerPort {
     pub fn new() -> Self {
         Self {
-            data: SyncSignal::new(0),
+            data: SharedData::new(0),
             ctrl: 0,
             th_count: 0,
             next_read: 0,
@@ -72,7 +71,7 @@ impl GenesisControllerPort {
     }
 }
 
-pub struct GenesisControllerUpdater(SyncSignal<u16>, SyncSignal<bool>);
+pub struct GenesisControllerUpdater(SharedData<u16>, SharedData<bool>);
 
 impl JoystickUpdater for GenesisControllerUpdater {
     fn update_joystick(&mut self, modifiers: u16) {
@@ -89,7 +88,7 @@ pub struct GenesisController {
     pub port_1: GenesisControllerPort,
     pub port_2: GenesisControllerPort,
     pub expansion: GenesisControllerPort,
-    pub interrupt: SyncSignal<bool>,
+    pub interrupt: SharedData<bool>,
 }
 
 impl GenesisController {
@@ -98,7 +97,7 @@ impl GenesisController {
             port_1: GenesisControllerPort::new(),
             port_2: GenesisControllerPort::new(),
             expansion: GenesisControllerPort::new(),
-            interrupt: SyncSignal::new(false),
+            interrupt: SharedData::new(false),
         }
     }
 
@@ -113,7 +112,7 @@ impl GenesisController {
         Ok(controller)
     }
 
-    pub fn get_interrupt_signal(&self) -> SyncSignal<bool> {
+    pub fn get_interrupt_signal(&self) -> SharedData<bool> {
         self.interrupt.clone()
     }
 }
diff --git a/src/peripherals/genesis/ym7101.rs b/src/peripherals/genesis/ym7101.rs
index 458c43e..37707b9 100644
--- a/src/peripherals/genesis/ym7101.rs
+++ b/src/peripherals/genesis/ym7101.rs
@@ -4,9 +4,8 @@ use std::sync::{Arc, Mutex};
 
 use crate::error::Error;
 use crate::system::System;
-use crate::signals::SyncSignal;
 use crate::devices::{Clock, ClockElapsed, Address, Addressable, Steppable, Transmutable, read_beu16, read_beu32, write_beu16};
-use crate::host::traits::{Host, BlitableSurface};
+use crate::host::traits::{Host, BlitableSurface, SharedData};
 use crate::host::gfx::{Frame, FrameSwapper};
 
 
@@ -410,11 +409,11 @@ impl<'a> Iterator for PatternIterator<'a> {
 pub struct Ym7101 {
     pub swapper: Arc<Mutex<FrameSwapper>>,
     pub state: Ym7101State,
-    pub external_interrupt: SyncSignal<bool>,
+    pub external_interrupt: SharedData<bool>,
 }
 
 impl Ym7101 {
-    pub fn new<H: Host>(host: &mut H, external_interrupt: SyncSignal<bool>) -> Ym7101 {
+    pub fn new<H: Host>(host: &mut H, external_interrupt: SharedData<bool>) -> Ym7101 {
         let swapper = FrameSwapper::new_shared(320, 224);
 
         host.add_window(FrameSwapper::to_boxed(swapper.clone())).unwrap();
diff --git a/src/peripherals/mc68681.rs b/src/peripherals/mc68681.rs
index e92db0d..0b1c64c 100644
--- a/src/peripherals/mc68681.rs
+++ b/src/peripherals/mc68681.rs
@@ -252,7 +252,7 @@ impl Steppable for MC68681 {
             self.set_interrupt_flag(ISR_CH_B_TX_READY, true);
         }
 
-        Ok(1_000_000_000 / 3_646_800)
+        Ok(1_000_000_000 / 3_686_400)
     }
 }
 
diff --git a/src/signals.rs b/src/signals.rs
index cbceb58..9a63395 100644
--- a/src/signals.rs
+++ b/src/signals.rs
@@ -1,7 +1,6 @@
 
 use std::rc::Rc;
-use std::cell::Cell;
-use std::sync::{Arc, Mutex};
+use std::cell::{Cell, RefCell, RefMut};
 
 #[derive(Clone, Debug)]
 pub struct Signal<T: Copy>(Rc<Cell<T>>);
@@ -20,22 +19,16 @@ impl<T: Copy> Signal<T> {
     }
 }
 
-
 #[derive(Clone, Debug)]
-pub struct SyncSignal<T: Copy>(Arc<Mutex<T>>);
+pub struct Latch<T>(Rc<RefCell<T>>);
 
-impl<T: Copy> SyncSignal<T> {
-    pub fn new(init: T) -> SyncSignal<T> {
-        SyncSignal(Arc::new(Mutex::new(init)))
+impl<T> Latch<T> {
+    pub fn new(init: T) -> Latch<T> {
+        Latch(Rc::new(RefCell::new(init)))
     }
 
-    pub fn set(&mut self, value: T) {
-        *(self.0.lock().unwrap()) = value;
-    }
-
-    pub fn get(&mut self) -> T {
-        *(self.0.lock().unwrap())
+    pub fn borrow_mut(&self) -> RefMut<'_, T> {
+        self.0.borrow_mut()
     }
 }
 
-
diff --git a/todo.txt b/todo.txt
index f5bfbc1..c0406be 100644
--- a/todo.txt
+++ b/todo.txt
@@ -30,7 +30,7 @@ Genesis/Mega Drive:
     * make tests for each instruction
     * check all instructions in the docs
 
-    * unimplemented: ABCD, ADDX, BFFFO, BFINS, BKPT, CHK, EXG, ILLEGAL, MOVEfromCCR, MOVEP, RTR, RTD, SBCD, SUBX
+    * unimplemented: ABCD, ADDX, BFFFO, BFINS, BKPT, CHK, ILLEGAL, MOVEfromCCR,, RTR, RTD, SBCD, SUBX
     * >=MC68020 undecoded & unimplemented: CALLM, CAS, CAS2, CHK2, CMP2, RTM, PACK, TRAPcc, UNPK
 
     * add support for MMU