diff --git a/src/kernel/exception.rs b/src/kernel/exception.rs
index a62042d..cf320d0 100644
--- a/src/kernel/exception.rs
+++ b/src/kernel/exception.rs
@@ -1,7 +1,7 @@
-use crate::simulator::machine::{ExceptionType, Machine};
+use crate::simulator::{machine::{ExceptionType, Machine}, error::{MachineOk, MachineError}};
 
 
-pub const SC_HALT: u8 =	0;
+pub const SC_SHUTDOWN: u8 =	0;
 pub const SC_EXIT: u8 =	1;
 pub const SC_EXEC: u8 =	2;
 pub const SC_JOIN: u8 =	3;
@@ -17,28 +17,28 @@ pub const SC_PERROR: u8 = 12;
 pub const SC_P: u8 = 13;
 pub const SC_V: u8 = 14;
 pub const SC_SEM_CREATE: u8 = 15 ;
-pub const SC_SEM_DESTROY: u8 =   16;
-pub const SC_LOCK_CREATE: u8 =	 17 ;
-pub const SC_LOCK_DESTROY: u8 =	 18 ;
-pub const SC_LOCK_ACQUIRE: u8 =	 19 ;
-pub const SC_LOCK_RELEASE: u8 =	 20 ;
-pub const SC_COND_CREATE: u8 =	 21 ;
-pub const SC_COND_DESTROY: u8 =	 22 ;
-pub const SC_COND_WAIT: u8 =	 23 ;
-pub const SC_COND_SIGNAL: u8 =	 24;
+pub const SC_SEM_DESTROY: u8 = 16;
+pub const SC_LOCK_CREATE: u8 = 17 ;
+pub const SC_LOCK_DESTROY: u8 = 18 ;
+pub const SC_LOCK_ACQUIRE: u8 = 19 ;
+pub const SC_LOCK_RELEASE: u8 = 20 ;
+pub const SC_COND_CREATE: u8 = 21 ;
+pub const SC_COND_DESTROY: u8 = 22 ;
+pub const SC_COND_WAIT: u8 = 23 ;
+pub const SC_COND_SIGNAL: u8 = 24;
 pub const SC_COND_BROADCAST: u8 = 25;
-pub const SC_TTY_SEND: u8 =	 26;
-pub const SC_TTY_RECEIVE: u8 =	 27;
-pub const SC_MKDIR: u8 =	 28;
-pub const SC_RMDIR: u8 =	 29;
-pub const SC_REMOVE: u8 =        30;
-pub const SC_FSLIST: u8 =        31;
-pub const SC_SYS_TIME: u8 =	 32 ;
-pub const SC_MMAP: u8 =		 33;
-pub const SC_DEBUG: u8 =         34;
+pub const SC_TTY_SEND: u8 = 26;
+pub const SC_TTY_RECEIVE: u8 = 27;
+pub const SC_MKDIR: u8 = 28;
+pub const SC_RMDIR: u8 = 29;
+pub const SC_REMOVE: u8 = 30;
+pub const SC_FSLIST: u8 = 31;
+pub const SC_SYS_TIME: u8 = 32 ;
+pub const SC_MMAP: u8 = 33;
+pub const SC_DEBUG: u8 = 34;
 
 
-pub fn call(exception: ExceptionType, machine: &Machine) {
+pub fn call(exception: ExceptionType, machine: &Machine) -> Result<MachineOk, MachineError> {
 
     match exception {
         ExceptionType::NoException => todo!(),
@@ -53,8 +53,45 @@ pub fn call(exception: ExceptionType, machine: &Machine) {
     }
 }
 
-fn syscall(machine: &Machine) {
-    let call_type = machine.read_int_register(17);
+fn syscall(machine: &Machine) -> Result<MachineOk, MachineError> {
+    let call_type = machine.read_int_register(17) as u8;
 
-    todo!()
+    match call_type {
+        SC_SHUTDOWN => Ok(MachineOk::Shutdown),
+        SC_EXIT => todo!(),
+        SC_EXEC => todo!(),
+        SC_JOIN => todo!(),
+        SC_CREATE => todo!(),
+        SC_OPEN => todo!(),
+        SC_READ => todo!(),
+        SC_WRITE => todo!(),
+        SC_SEEK => todo!(),
+        SC_CLOSE => todo!(),
+        SC_NEW_THREAD => todo!(),
+        SC_YIELD => todo!(),
+        SC_PERROR => todo!(),
+        SC_P => todo!(),
+        SC_V => todo!(),
+        SC_SEM_CREATE => todo!(),
+        SC_SEM_DESTROY => todo!(),
+        SC_LOCK_CREATE => todo!(),
+        SC_LOCK_DESTROY => todo!(),
+        SC_LOCK_ACQUIRE => todo!(),
+        SC_LOCK_RELEASE => todo!(),
+        SC_COND_CREATE => todo!(),
+        SC_COND_DESTROY => todo!(),
+        SC_COND_WAIT => todo!(),
+        SC_COND_SIGNAL => todo!(),
+        SC_COND_BROADCAST => todo!(),
+        SC_TTY_SEND => todo!(),
+        SC_TTY_RECEIVE => todo!(),
+        SC_MKDIR => todo!(),
+        SC_RMDIR => todo!(),
+        SC_REMOVE => todo!(),
+        SC_FSLIST => todo!(),
+        SC_SYS_TIME => todo!(),
+        SC_MMAP => todo!(),
+        SC_DEBUG => todo!(),
+        _ => todo!()
+    }
 }
\ No newline at end of file
diff --git a/src/simulator/machine.rs b/src/simulator/machine.rs
index a4bcdaa..9e4b4af 100644
--- a/src/simulator/machine.rs
+++ b/src/simulator/machine.rs
@@ -230,7 +230,13 @@ impl Machine {
 
 		self.set_status(MachineStatus::SystemMode);
 		// Handle the interruption
-		exception::call(exception, self); // todo: return error if the syscall code is invalid 
+		match exception::call(exception, self) {
+			Ok(MachineOk::Shutdown) => {
+				self.set_status(MachineStatus::UserMode);
+				return Ok(MachineOk::Shutdown);
+			}
+			_ => ()
+		} // todo: return error if the syscall code is invalid 
 		self.set_status(MachineStatus::UserMode);
 		Ok(MachineOk::Ok)
 	}
@@ -243,7 +249,8 @@ impl Machine {
 	pub fn run(&mut self) {
 		loop {
 			match self.one_instruction() {
-				Ok(_) => println!("hello"),
+				Ok(MachineOk::Ok) => println!("hello"),
+				Ok(MachineOk::Shutdown) => break,
 				Err(e) => { if e.to_string().contains("System") { break; } panic!("FATAL at pc {} -> {}", self.pc, e) }
 			}
 		}