diff --git a/kern/env.c b/kern/env.c
index df3a9cd..661b8dd 100644
--- a/kern/env.c
+++ b/kern/env.c
@@ -255,6 +255,7 @@ env_alloc(struct Env **newenv_store, envid_t parent_id)
 
 	// Enable interrupts while in user mode.
 	// LAB 4: Your code here.
+	e->env_tf.tf_eflags |= FL_IF;
 
 	// Clear the page fault handler until user installs one.
 	e->env_pgfault_upcall = 0;
diff --git a/kern/sched.c b/kern/sched.c
index cba0cac..3062cdc 100644
--- a/kern/sched.c
+++ b/kern/sched.c
@@ -93,7 +93,7 @@ sched_halt(void)
 		"pushl $0\n"
         // LAB 4:
 		// Uncomment the following line after completing exercise 13
-		//"sti\n"
+		"sti\n"
 		"1:\n"
 		"hlt\n"
 		"jmp 1b\n"
diff --git a/kern/syscall.c b/kern/syscall.c
index ca3a35c..269c9f1 100644
--- a/kern/syscall.c
+++ b/kern/syscall.c
@@ -294,8 +294,38 @@ sys_page_unmap(envid_t envid, void *va)
 static int
 sys_ipc_try_send(envid_t envid, uint32_t value, void *srcva, unsigned perm)
 {
-	// LAB 4: Your code here.
-	panic("sys_ipc_try_send not implemented");
+	struct Env* dest_env;
+	struct Env* src_env;
+	int return_code;
+
+	if((return_code = envid2env(0, &src_env, 0)) < 0)
+		return return_code;
+	if((return_code = envid2env(envid, &dest_env, 0)) < 0)
+		return return_code;
+
+	if(!dest_env->env_ipc_recving)
+		return -E_IPC_NOT_RECV;
+
+	if((uintptr_t) srcva < UTOP && dest_env->env_ipc_dstva) {
+		if(!SYS_CHECKADDR(srcva)) return -E_INVAL;
+		if(!SYS_CHECKPERMS(perm)) return -E_INVAL;
+
+		pte_t* srcpte;
+		struct PageInfo* page = page_lookup(src_env->env_pgdir, srcva, &srcpte);
+		if(page == NULL) return -E_INVAL;
+		if(perm & PTE_W && !(*srcpte & PTE_W)) return -E_INVAL;
+
+		page_insert(dest_env->env_pgdir, page, dest_env->env_ipc_dstva, perm);
+		dest_env->env_ipc_perm = perm;
+	}
+
+	dest_env->env_ipc_from = src_env->env_id;
+	dest_env->env_ipc_value = value;
+	dest_env->env_ipc_recving = false;
+	if(dest_env->env_status == ENV_NOT_RUNNABLE)
+		dest_env->env_status = ENV_RUNNABLE;
+
+	return 0;
 }
 
 // Block until a value is ready.  Record that you want to receive
@@ -312,8 +342,20 @@ sys_ipc_try_send(envid_t envid, uint32_t value, void *srcva, unsigned perm)
 static int
 sys_ipc_recv(void *dstva)
 {
+	struct Env* env;
+	int return_code;
+
+	if((return_code = envid2env(0, &env, 1)) < 0)
+		return return_code;
+
 	// LAB 4: Your code here.
-	panic("sys_ipc_recv not implemented");
+	if((uintptr_t) dstva < UTOP) {
+		if(!SYS_CHECKADDR(dstva)) return -E_INVAL;
+		env->env_ipc_dstva = dstva;
+	}
+	env->env_ipc_recving = true;
+	env->env_status = ENV_NOT_RUNNABLE;
+
 	return 0;
 }
 
@@ -350,6 +392,10 @@ syscall(uint32_t syscallno, uint32_t a1, uint32_t a2, uint32_t a3, uint32_t a4,
 		return sys_page_map(a1, (void*) a2, a3, (void*) a4, a5);
 	case SYS_page_unmap:
 		return sys_page_unmap(a1, (void*) a2);
+	case SYS_ipc_try_send:
+		return sys_ipc_try_send(a1, a2, (void*) a3, a4);
+	case SYS_ipc_recv:
+		return sys_ipc_recv((void*) a1);
 	default:
 		return -E_INVAL;
 	}
diff --git a/kern/trap.c b/kern/trap.c
index 6cf1d88..478149d 100644
--- a/kern/trap.c
+++ b/kern/trap.c
@@ -89,6 +89,13 @@ void t_simderr();
 void t_syscall();
 void t_default();
 
+void irq_timer();
+void irq_kbd();
+void irq_serial();
+void irq_spurious();
+void irq_ide();
+void irq_error();
+
 void
 trap_init(void)
 {
@@ -125,6 +132,13 @@ trap_init(void)
 	SETGATE(idt[T_SYSCALL], 0, GD_KT, t_syscall, 3);
 	SETGATE(idt[T_DEFAULT], 0, GD_KT, t_default, 0);
 
+	SETGATE(idt[IRQ_OFFSET + IRQ_TIMER], 0, GD_KT, irq_timer, 0);
+	SETGATE(idt[IRQ_OFFSET + IRQ_KBD], 0, GD_KT, irq_kbd, 0);
+	SETGATE(idt[IRQ_OFFSET + IRQ_SERIAL], 0, GD_KT, irq_serial, 0);
+	SETGATE(idt[IRQ_OFFSET + IRQ_SPURIOUS], 0, GD_KT, irq_spurious, 0);
+	SETGATE(idt[IRQ_OFFSET + IRQ_IDE], 0, GD_KT, irq_ide, 0);
+	SETGATE(idt[IRQ_OFFSET + IRQ_ERROR], 0, GD_KT, irq_error, 0);
+
 	// Per-CPU setup
 	trap_init_percpu();
 }
@@ -243,6 +257,9 @@ trap_dispatch(struct Trapframe *tf)
 				tf->tf_regs.reg_esi);
 		tf->tf_regs.reg_eax = returned;
 		return;
+	} else if (tf->tf_trapno == IRQ_OFFSET + IRQ_TIMER) {
+		lapic_eoi();
+		sched_yield();
 	}
 
 	// Handle spurious interrupts
diff --git a/kern/trapentry.S b/kern/trapentry.S
index fb2a3c7..180061a 100644
--- a/kern/trapentry.S
+++ b/kern/trapentry.S
@@ -82,6 +82,12 @@ TRAPHANDLER_NOEC(t_mchk, T_MCHK);
 TRAPHANDLER_NOEC(t_simderr, T_SIMDERR);
 TRAPHANDLER_NOEC(t_syscall, T_SYSCALL);
 TRAPHANDLER(t_default, T_DEFAULT);
+TRAPHANDLER_NOEC(irq_timer, IRQ_OFFSET + IRQ_TIMER);
+TRAPHANDLER_NOEC(irq_kbd, IRQ_OFFSET + IRQ_KBD);
+TRAPHANDLER_NOEC(irq_serial, IRQ_OFFSET + IRQ_SERIAL);
+TRAPHANDLER_NOEC(irq_spurious, IRQ_OFFSET + IRQ_SPURIOUS);
+TRAPHANDLER_NOEC(irq_ide, IRQ_OFFSET + IRQ_IDE);
+TRAPHANDLER_NOEC(irq_error, IRQ_OFFSET + IRQ_ERROR);
 
 // HINT 1 : TRAPHANDLER_NOEC(t_divide, T_DIVIDE);
 //          Do something like this if there is no error code for the trap
diff --git a/lib/ipc.c b/lib/ipc.c
index 2e222b9..fba6247 100644
--- a/lib/ipc.c
+++ b/lib/ipc.c
@@ -22,9 +22,14 @@
 int32_t
 ipc_recv(envid_t *from_env_store, void *pg, int *perm_store)
 {
-	// LAB 4: Your code here.
-	panic("ipc_recv not implemented");
-	return 0;
+	int return_code;
+	if((return_code = sys_ipc_recv(pg ? pg : (void*) ~0)) < 0)
+		return return_code;
+
+	if(from_env_store) *from_env_store = thisenv->env_ipc_from;
+	if(perm_store) *perm_store = thisenv->env_ipc_perm;
+
+	return thisenv->env_ipc_value;
 }
 
 // Send 'val' (and 'pg' with 'perm', if 'pg' is nonnull) to 'toenv'.
@@ -38,8 +43,12 @@ ipc_recv(envid_t *from_env_store, void *pg, int *perm_store)
 void
 ipc_send(envid_t to_env, uint32_t val, void *pg, int perm)
 {
-	// LAB 4: Your code here.
-	panic("ipc_send not implemented");
+	int return_code = -E_IPC_NOT_RECV;
+	while(return_code == -E_IPC_NOT_RECV) {
+		return_code = sys_ipc_try_send(to_env, val, pg ? pg : (void*) ~0, perm);
+		sys_yield();
+	}
+	if(return_code != 0) panic("failed to send\n");
 }
 
 // Find the first environment of the given type.  We'll use this to