diff --git a/src/mem.rs b/src/mem.rs
index 21cabec..5576905 100644
--- a/src/mem.rs
+++ b/src/mem.rs
@@ -349,17 +349,38 @@ pub struct DeviceEntry {
     pub interface: Arc<dyn MemDeviceInterface>,
 }
 
+#[allow(unused_variables)]
 pub trait MemDeviceInterface {
-    fn write_dword(&self, page: PageNum, offset: u16, value: DWord) -> Result<(), ExceptionType>;
-    fn write_word(&self, page: PageNum, offset: u16, value: Word) -> Result<(), ExceptionType>;
-    fn write_hword(&self, page: PageNum, offset: u16, value: HWord) -> Result<(), ExceptionType>;
-    fn write_byte(&self, page: PageNum, offset: u16, value: Byte) -> Result<(), ExceptionType>;
+    fn write_dword(&self, page: PageNum, offset: u16, value: DWord) -> Result<(), ExceptionType> {
+        Err(ExceptionType::StoreAmoAccessFault)
+    }
+    fn write_word(&self, page: PageNum, offset: u16, value: Word) -> Result<(), ExceptionType> {
+        Err(ExceptionType::StoreAmoAccessFault)
+    }
+    fn write_hword(&self, page: PageNum, offset: u16, value: HWord) -> Result<(), ExceptionType> {
+        Err(ExceptionType::StoreAmoAccessFault)
+    }
+    fn write_byte(&self, page: PageNum, offset: u16, value: Byte) -> Result<(), ExceptionType> {
+        Err(ExceptionType::StoreAmoAccessFault)
+    }
 
-    fn read_dword(&self, page: PageNum, offset: u16) -> Result<DWord, ExceptionType>;
-    fn read_word(&self, page: PageNum, offset: u16) -> Result<Word, ExceptionType>;
-    fn read_hword(&self, page: PageNum, offset: u16) -> Result<HWord, ExceptionType>;
-    fn read_byte(&self, page: PageNum, offset: u16) -> Result<Byte, ExceptionType>;
+    fn read_dword(&self, page: PageNum, offset: u16) -> Result<DWord, ExceptionType> {
+        Err(ExceptionType::LoadAccessFault)
+    }
+    fn read_word(&self, page: PageNum, offset: u16) -> Result<Word, ExceptionType> {
+        Err(ExceptionType::LoadAccessFault)
+    }
+    fn read_hword(&self, page: PageNum, offset: u16) -> Result<HWord, ExceptionType> {
+        Err(ExceptionType::LoadAccessFault)
+    }
+    fn read_byte(&self, page: PageNum, offset: u16) -> Result<Byte, ExceptionType> {
+        Err(ExceptionType::LoadAccessFault)
+    }
 
-    fn get_atomic_word(&self, page: PageNum, offset: u16) -> Result<&AtomicU32, ExceptionType>;
-    fn get_atomic_dword(&self, page: PageNum, offset: u16) -> Result<&AtomicU64, ExceptionType>;
+    fn get_atomic_word(&self, page: PageNum, offset: u16) -> Result<&AtomicU32, ExceptionType> {
+        Err(ExceptionType::StoreAmoAccessFault)
+    }
+    fn get_atomic_dword(&self, page: PageNum, offset: u16) -> Result<&AtomicU64, ExceptionType> {
+        Err(ExceptionType::StoreAmoAccessFault)
+    }
 }