diff --git a/src/arm7tdmi/arm/exec.rs b/src/arm7tdmi/arm/exec.rs
index 3453bdb..8427968 100644
--- a/src/arm7tdmi/arm/exec.rs
+++ b/src/arm7tdmi/arm/exec.rs
@@ -13,7 +13,7 @@ use super::{
 };
 
 impl Core {
-    pub fn exec_arm(&mut self, sysbus: &mut SysBus, insn: ArmInstruction) -> CpuExecResult {
+    pub fn exec_arm(&mut self, sysbus: &mut Bus, insn: ArmInstruction) -> CpuExecResult {
         if !self.check_arm_cond(insn.cond) {
             self.add_cycles(
                 insn.pc + (self.word_size() as u32),
@@ -41,7 +41,7 @@ impl Core {
     /// Cycles 2S+1N
     fn exec_b_bl(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
         insn: ArmInstruction,
     ) -> CpuResult<CpuPipelineAction> {
         if insn.link_flag() {
@@ -67,7 +67,7 @@ impl Core {
     /// Cycles 2S+1N
     fn exec_bx(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
         insn: ArmInstruction,
     ) -> CpuResult<CpuPipelineAction> {
         let rn = self.get_reg(insn.rn());
@@ -95,7 +95,7 @@ impl Core {
 
     fn exec_swi(
         &mut self,
-        _sysbus: &mut SysBus,
+        _sysbus: &mut Bus,
         _insn: ArmInstruction,
     ) -> CpuResult<CpuPipelineAction> {
         self.exception(Exception::SoftwareInterrupt);
@@ -104,7 +104,7 @@ impl Core {
 
     fn exec_msr_reg(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
         insn: ArmInstruction,
     ) -> CpuResult<CpuPipelineAction> {
         let new_psr = RegPSR::new(self.get_reg(insn.rm()));
@@ -202,7 +202,7 @@ impl Core {
     ///         Add x=1I cycles if Op2 shifted-by-register. Add y=1S+1N cycles if Rd=R15.
     fn exec_data_processing(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
         insn: ArmInstruction,
     ) -> CpuResult<CpuPipelineAction> {
         // TODO handle carry flag
@@ -287,7 +287,7 @@ impl Core {
     /// For LDR, add y=1S+1N if Rd=R15.
     fn exec_ldr_str(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
         insn: ArmInstruction,
     ) -> CpuResult<CpuPipelineAction> {
         if insn.write_back_flag() && insn.rd() == insn.rn() {
diff --git a/src/arm7tdmi/cpu.rs b/src/arm7tdmi/cpu.rs
index 6d493b3..0c8203b 100644
--- a/src/arm7tdmi/cpu.rs
+++ b/src/arm7tdmi/cpu.rs
@@ -183,7 +183,7 @@ impl Core {
         self.cycles += 1;
     }
 
-    pub fn add_cycles(&mut self, addr: Addr, sysbus: &SysBus, access: MemoryAccess) {
+    pub fn add_cycles(&mut self, addr: Addr, sysbus: &Bus, access: MemoryAccess) {
         self.cycles += sysbus.get_cycles(addr, access);
     }
 
@@ -210,7 +210,7 @@ impl Core {
 
     fn step_thumb(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
     ) -> CpuResult<(Option<DecodedInstruction>, CpuPipelineAction)> {
         // fetch
         let new_fetched = sysbus.read_16(self.pc);
@@ -244,7 +244,7 @@ impl Core {
 
     fn step_arm(
         &mut self,
-        sysbus: &mut SysBus,
+        sysbus: &mut Bus,
     ) -> CpuResult<(Option<DecodedInstruction>, CpuPipelineAction)> {
         // fetch
         let new_fetched = sysbus.read_32(self.pc);
@@ -278,7 +278,7 @@ impl Core {
 
     /// Perform a pipeline step
     /// If an instruction was executed in this step, return it.
-    pub fn step(&mut self, sysbus: &mut SysBus) -> CpuResult<Option<DecodedInstruction>> {
+    pub fn step(&mut self, sysbus: &mut Bus) -> CpuResult<Option<DecodedInstruction>> {
         let (executed_instruction, pipeline_action) = match self.cpsr.state() {
             CpuState::ARM => self.step_arm(sysbus),
             CpuState::THUMB => self.step_thumb(sysbus),
@@ -326,7 +326,7 @@ impl Core {
     /// A step that returns only once an instruction was executed.
     /// Returns the address of PC before executing an instruction,
     /// and the address of the next instruction to be executed;
-    pub fn step_debugger(&mut self, sysbus: &mut SysBus) -> CpuResult<DecodedInstruction> {
+    pub fn step_debugger(&mut self, sysbus: &mut Bus) -> CpuResult<DecodedInstruction> {
         loop {
             if let Some(i) = self.step(sysbus)? {
                 return Ok(i);
diff --git a/src/arm7tdmi/thumb/exec.rs b/src/arm7tdmi/thumb/exec.rs
index 63b8d97..bbfe2ff 100644
--- a/src/arm7tdmi/thumb/exec.rs
+++ b/src/arm7tdmi/thumb/exec.rs
@@ -1,9 +1,9 @@
-use super::super::super::sysbus::SysBus;
 use super::super::cpu::{Core, CpuExecResult};
 use super::ThumbInstruction;
+use crate::arm7tdmi::bus::Bus;
 
 impl Core {
-    pub fn exec_thumb(&mut self, sysbus: &mut SysBus, insn: ThumbInstruction) -> CpuExecResult {
+    pub fn exec_thumb(&mut self, sysbus: &mut Bus, insn: ThumbInstruction) -> CpuExecResult {
         unimplemented!("thumb not implemented {:#}", insn)
     }
 }
diff --git a/src/sysbus.rs b/src/sysbus.rs
index c56db7c..00dc3b8 100644
--- a/src/sysbus.rs
+++ b/src/sysbus.rs
@@ -92,7 +92,7 @@ impl SysBus {
         }
     }
 
-    fn map(&self, addr: Addr) -> &impl Bus {
+    fn map(&self, addr: Addr) -> & Bus {
         match addr as usize {
             0x0000_0000...0x0000_3fff => &self.bios,
             0x0200_0000...0x0203_ffff => &self.onboard_work_ram,
@@ -107,7 +107,7 @@ impl SysBus {
     }
 
     /// TODO proc-macro for generating this function
-    fn map_mut(&mut self, addr: Addr) -> &mut impl Bus {
+    fn map_mut(&mut self, addr: Addr) -> &mut Bus {
         match addr as usize {
             0x0000_0000...0x0000_3fff => &mut self.bios,
             0x0200_0000...0x0203_ffff => &mut self.onboard_work_ram,