diff --git a/src/kernel/exception.rs b/src/kernel/exception.rs
index 64b7e28..de86c49 100644
--- a/src/kernel/exception.rs
+++ b/src/kernel/exception.rs
@@ -203,7 +203,7 @@ fn syscall(machine: &mut Machine, system: &mut System) -> Result<MachineOk, Mach
         },
         SC_YIELD => todo!(),
         SC_PERROR => todo!(),
-        SC_P => todo!(),
+        SC_P => sc_p(machine, system),
         SC_V => sc_v(machine, system),
         SC_SEM_CREATE => {
             let addr_name = machine.read_int_register(10) as usize;
@@ -240,7 +240,15 @@ fn syscall(machine: &mut Machine, system: &mut System) -> Result<MachineOk, Mach
     }
 }
 
-fn sc_v(machine: &mut Machine, system: &mut System) -> Result<(), Error>{
+fn sc_p(machine: &mut Machine, system: &mut System) -> Result<(), Error> {
+    let id_sema = machine.int_reg.get_reg(10);
+    match system.get_obj_addrs().search_semaphore(id_sema) {
+        Some(sema) => { sema.p(machine, system.get_thread_manager()); Ok(()) }
+        None => Err(format!("Coudn't find semaphore {}", id_sema))
+    }
+}
+
+fn sc_v(machine: &mut Machine, system: &mut System) -> Result<(), Error> {
     let id_sema = machine.int_reg.get_reg(10);
     match system.get_obj_addrs().search_semaphore(id_sema) {
         Some(sema) => { sema.v(machine, system.get_thread_manager()); Ok(()) },