diff --git a/13_day/bootpack.h b/13_day/bootpack.h
index 1ca75e6..dc74f6f 100644
--- a/13_day/bootpack.h
+++ b/13_day/bootpack.h
@@ -169,13 +169,14 @@ void sheet_free(struct SHEET *sht);
 /* timer.c */
 #define MAX_TIMER 500
 struct TIMER {
+	struct TIMER *next;
 	unsigned int timeout, flags;
 	struct FIFO32 *fifo;
 	int data;
 };
 struct TIMERCTL {
 	unsigned int count, next, using;
-	struct TIMER *timers[MAX_TIMER];
+	struct TIMER *t0;
 	struct TIMER timers0[MAX_TIMER];
 };
 extern struct TIMERCTL timerctl;
diff --git a/13_day/timer.c b/13_day/timer.c
index a987db8..11ed780 100644
--- a/13_day/timer.c
+++ b/13_day/timer.c
@@ -52,53 +52,79 @@ void timer_init(struct TIMER *timer, struct FIFO32 *fifo, int data)
 
 void timer_settime(struct TIMER *timer, unsigned int timeout)
 {
-	int e, i, j;
+	int e;
+	struct TIMER *t, *s;
 	timer->timeout = timeout + timerctl.count;
 	timer->flags = TIMER_FLAGS_USING;
 	e = io_load_eflags();
 	io_cli();
-	/* 搜索注册位置 */
-	for (i = 0; i < timerctl.using; i++) {
-		if (timerctl.timers[i]->timeout >= timer->timeout) {
-			break;
+	timerctl.using++;
+	if (timerctl.using == 1) {
+	/* 处于运行状态的定时器只有这一个时 */
+		timerctl.t0 = timer;
+		timer->next = 0; /* 没有下一个 */
+		timerctl.next = timer->timeout;
+		io_store_eflags(e);
+		return;
+	}
+	t = timerctl.t0;
+	if (timer->timeout <= t->timeout) {
+	/* 插入最前面的情况下 */
+		timerctl.t0 = timer;
+		timer->next = t; /* 下面是t */
+		timerctl.next = timer->timeout;
+		io_store_eflags(e);
+		return;
+	}
+	/* 搜寻插入位置 */
+	for (;;) {
+		s = t;
+		t = t->next;
+		if (t == 0) {
+			break; /* 最后面*/
+		}
+		if (timer->timeout <= t->timeout) {
+		/* 插入到s和t之间时 */
+			s->next = timer; /* s的下一个是timer */
+			timer->next = t; /* timer的下一个是t */
+			io_store_eflags(e);
+			return;
 		}
 	}
-	/* i号之后全部后移一位 */
-	for (j = timerctl.using; j > i; j--) {
-		timerctl.timers[j] = timerctl.timers[j - 1];
-	}
-	timerctl.using++;
-	/* 插入到空位上 */
-	timerctl.timers[i] = timer;
-	timerctl.next = timerctl.timers[0]->timeout;
+	/* 插入最后面的情况下 */
+	s->next = timer;
+	timer->next = 0;
 	io_store_eflags(e);
 	return;
 }
 
 void inthandler20(int *esp)
 {
-	int i, j;
+	int i;
+	struct TIMER *timer;
 	io_out8(PIC0_OCW2, 0x60); /* 把IRQ-00信号接收完了的信息通知给PIC */
 	timerctl.count++;
 	if (timerctl.next > timerctl.count) {
 		return; /* 还不到下一个时刻，所以结束*/
 	}
+	timer = timerctl.t0; /* 首先把最前面的地址赋给timer */
 	for (i = 0; i < timerctl.using; i++) {
-		/* timers的定时器都处于动作中，所以不确认flags */
-		if (timerctl.timers[i]->timeout > timerctl.count) {
+		/* 因为timers的定时器都处于运行状态，所以不确认flags */
+		if (timer->timeout > timerctl.count) {
 			break;
 		}
 		/* 超时*/
-		timerctl.timers[i]->flags = TIMER_FLAGS_ALLOC;
-		fifo32_put(timerctl.timers[i]->fifo, timerctl.timers[i]->data);
+		timer->flags = TIMER_FLAGS_ALLOC;
+		fifo32_put(timer->fifo, timer->data);
+		timer = timer->next; /* 下一定时器的地址赋给timer */
 	}
 	/* 正好有i个定时器超时了。其余的进行移位。 */
 	timerctl.using -= i;
-	for (j = 0; j < timerctl.using; j++) {
-		timerctl.timers[j] = timerctl.timers[i + j];
-	}
+	/* 新移位 */
+	timerctl.t0 = timer;
+	/* timerctl.next的设定 */
 	if (timerctl.using > 0) {
-		timerctl.next = timerctl.timers[0]->timeout;
+		timerctl.next = timerctl.t0->timeout;
 	} else {
 		timerctl.next = 0xffffffff;
 	}