diff --git a/ch3-coop/user/src/bin/00hello_world.rs b/ch3-coop/user/src/bin/00hello_world.rs
deleted file mode 100644
index e1391d7..0000000
--- a/ch3-coop/user/src/bin/00hello_world.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-#![no_std]
-#![no_main]
-
-use user_lib::*;
-
-#[no_mangle]
-fn main() -> i32 {
-    println!("hello 1");
-    0
-}
\ No newline at end of file
diff --git a/ch3-coop/user/src/bin/00write_a.rs b/ch3-coop/user/src/bin/00write_a.rs
new file mode 100644
index 0000000..8bebc9d
--- /dev/null
+++ b/ch3-coop/user/src/bin/00write_a.rs
@@ -0,0 +1,23 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::yield_;
+
+const WIDTH: usize = 10;
+const HEIGHT: usize = 5;
+
+#[no_mangle]
+fn main() -> i32 {
+    for i in 0..HEIGHT {
+        for _ in 0..WIDTH {
+            print!("A");
+        }
+        println!(" [{}/{}]", i + 1, HEIGHT);
+        yield_();
+    }
+    println!("Test write_a OK!");
+    0
+}
diff --git a/ch3-coop/user/src/bin/01store_fault.rs b/ch3-coop/user/src/bin/01store_fault.rs
deleted file mode 100644
index f8023eb..0000000
--- a/ch3-coop/user/src/bin/01store_fault.rs
+++ /dev/null
@@ -1,15 +0,0 @@
-#![no_std]
-#![no_main]
-
-#[macro_use]
-extern crate user_lib;
-
-#[no_mangle]
-fn main() -> i32 {
-    println!("Into Test store_fault, we will insert an invalid store operation...");
-    println!("Kernel should kill this application!");
-    unsafe {
-        core::ptr::null_mut::<u8>().write_volatile(0);
-    }
-    0
-}
diff --git a/ch3-coop/user/src/bin/01write_b.rs b/ch3-coop/user/src/bin/01write_b.rs
new file mode 100644
index 0000000..652d5dd
--- /dev/null
+++ b/ch3-coop/user/src/bin/01write_b.rs
@@ -0,0 +1,23 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::yield_;
+
+const WIDTH: usize = 10;
+const HEIGHT: usize = 2;
+
+#[no_mangle]
+fn main() -> i32 {
+    for i in 0..HEIGHT {
+        for _ in 0..WIDTH {
+            print!("B");
+        }
+        println!(" [{}/{}]", i + 1, HEIGHT);
+        yield_();
+    }
+    println!("Test write_b OK!");
+    0
+}
diff --git a/ch3-coop/user/src/bin/02power.rs b/ch3-coop/user/src/bin/02power.rs
deleted file mode 100644
index f628f34..0000000
--- a/ch3-coop/user/src/bin/02power.rs
+++ /dev/null
@@ -1,27 +0,0 @@
-#![no_std]
-#![no_main]
-
-#[macro_use]
-extern crate user_lib;
-
-const SIZE: usize = 10;
-const P: u32 = 3;
-const STEP: usize = 100000;
-const MOD: u32 = 10007;
-
-#[no_mangle]
-fn main() -> i32 {
-    let mut pow = [0u32; SIZE];
-    let mut index: usize = 0;
-    pow[index] = 1;
-    for i in 1..=STEP {
-        let last = pow[index];
-        index = (index + 1) % SIZE;
-        pow[index] = last * P % MOD;
-        if i % 10000 == 0 {
-            println!("{}^{}={}(MOD {})", P, i, pow[index], MOD);
-        }
-    }
-    println!("Test power OK!");
-    0
-}
diff --git a/ch3-coop/user/src/bin/02write_c.rs b/ch3-coop/user/src/bin/02write_c.rs
new file mode 100644
index 0000000..9bed4da
--- /dev/null
+++ b/ch3-coop/user/src/bin/02write_c.rs
@@ -0,0 +1,23 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::yield_;
+
+const WIDTH: usize = 10;
+const HEIGHT: usize = 3;
+
+#[no_mangle]
+fn main() -> i32 {
+    for i in 0..HEIGHT {
+        for _ in 0..WIDTH {
+            print!("C");
+        }
+        println!(" [{}/{}]", i + 1, HEIGHT);
+        yield_();
+    }
+    println!("Test write_c OK!");
+    0
+}
diff --git a/ch3-coop/user/src/bin/03priv_inst.rs b/ch3-coop/user/src/bin/03priv_inst.rs
deleted file mode 100644
index 04dac37..0000000
--- a/ch3-coop/user/src/bin/03priv_inst.rs
+++ /dev/null
@@ -1,17 +0,0 @@
-#![no_std]
-#![no_main]
-
-#[macro_use]
-extern crate user_lib;
-
-use core::arch::asm;
-
-#[no_mangle]
-fn main() -> i32 {
-    println!("Try to execute privileged instruction in U Mode");
-    println!("Kernel should kill this application!");
-    unsafe {
-        asm!("sret");
-    }
-    0
-}
diff --git a/ch3-coop/user/src/bin/04priv_csr.rs b/ch3-coop/user/src/bin/04priv_csr.rs
deleted file mode 100644
index fbd678f..0000000
--- a/ch3-coop/user/src/bin/04priv_csr.rs
+++ /dev/null
@@ -1,17 +0,0 @@
-#![no_std]
-#![no_main]
-
-#[macro_use]
-extern crate user_lib;
-
-use riscv::register::sstatus::{self, SPP};
-
-#[no_mangle]
-fn main() -> i32 {
-    println!("Try to access privileged CSR in U Mode");
-    println!("Kernel should kill this application!");
-    unsafe {
-        sstatus::set_spp(SPP::User);
-    }
-    0
-}