diff --git a/src/list/src/list.h b/src/list/src/list.h
index c0075dd..b3214ad 100644
--- a/src/list/src/list.h
+++ b/src/list/src/list.h
@@ -120,6 +120,9 @@ list_iterator_new_from_node(list_node_t *node, list_direction_t direction);
 list_node_t *
 list_iterator_next(list_iterator_t *self);
 
+list_node_t *
+list_iterator_prev(list_iterator_t *self);
+
 void
 list_iterator_destroy(list_iterator_t *self);
 
diff --git a/src/list/src/list_iterator.c b/src/list/src/list_iterator.c
index f1363b2..c0edbc6 100644
--- a/src/list/src/list_iterator.c
+++ b/src/list/src/list_iterator.c
@@ -51,6 +51,22 @@ list_iterator_next(list_iterator_t *self) {
   return curr;
 }
 
+/*
+ * Return the previous list_node_t or NULL when no more
+ * nodes remain in the list.
+ */
+
+list_node_t *
+list_iterator_prev(list_iterator_t *self) {
+  list_node_t *curr = self->next;
+  if (curr) {
+    self->next = self->direction == LIST_HEAD
+      ? curr->prev
+      : curr->next;
+  }
+  return curr;
+}
+
 /*
  * Free the list iterator.
  */
diff --git a/testline.c b/testline.c
index f952b28..69d342b 100644
--- a/testline.c
+++ b/testline.c
@@ -2,6 +2,12 @@
 #include <string.h>
 #include "src/list/src/list.h"
 
+typedef enum InfoRet {
+  IR_UNKNOWN = -1,
+  IR_NORMAL = 0,
+  IR_UNSUCCESS
+} InfoRet;
+
 
 typedef struct InfoState {
   char* info;
@@ -100,10 +106,9 @@ void initInfoState(InfoState* st, char* text) {
   st->pos2 = st->pos3 = NULL;
 }
 
-int initInfoScreen(InfoState* st, char* text) {
+InfoRet initInfoScreen(InfoState* st, char* text) {
   initInfoState(st, text);
   printf("%d\n", st->wrap->len);
-  int retn = 0;
   //lcd.setCursor(0, 0);
   if ((st->pos2 = list_iterator_next(st->it))) {
     //printf("hello\n");
@@ -123,12 +128,34 @@ int initInfoScreen(InfoState* st, char* text) {
       lcd_blank_line();
     }
   } else {
-    retn = 1;
+    return IR_UNKNOWN;
   }
-  return retn;
+  return IR_NORMAL;
 }
 
-int scrollDown(InfoState* st) {
+InfoRet scrollDown(InfoState* st) {
+  if (st->pos2) {
+    st->pos1 = st->pos2;
+  } else {
+    return IR_UNKNOWN;
+  }
+  if (st->pos3) {
+    st->pos2 = st->pos3;
+  } else {
+    return IR_UNSUCCESS;
+  }
+  int tmp = lcd_print_between(st->info, (int)st->pos1->val, (int)st->pos2->val);
+  if ((st->pos3 = list_iterator_next(st->it))) {
+    printf("\n");
+    int tmp = lcd_print_between(st->info, (int)st->pos2->val, (int)st->pos3->val);
+  } else {
+    printf("\n");
+    lcd_blank_line();
+  }
+  return IR_NORMAL;
+}
+
+InfoRet scrollUp(InfoState* st) {
   
 }
 
@@ -208,8 +235,25 @@ int main() {
   list_node_t *node;
   list_iterator_t *it = list_iterator_new(wrap, LIST_HEAD);
   
+  node = list_iterator_next(it);
+  printf("node val: %d\n", node->val);
+  node = list_iterator_next(it);
+  printf("node val: %d\n", node->val);
+  node = list_iterator_prev(it);
+  printf("node val: %d\n", node->val);
+  node = list_iterator_prev(it);
+  printf("node val: %d\n", node->val);
+  node = list_iterator_prev(it);
+  printf("node val: %d\n", node->val);
+  
+  InfoRet ret_code;
   InfoState st;
   initInfoScreen(&st, cinfo);
+  for (int i = 0; i < 10; ++i) {
+    printf("\n");
+    ret_code = scrollDown(&st);
+    printf("\n%d\n", ret_code);
+  }
   
  /* 
   while ((node = list_iterator_next(it))) {