diff --git a/os/Cargo.lock b/os/Cargo.lock
index b85588b1..85e21762 100644
--- a/os/Cargo.lock
+++ b/os/Cargo.lock
@@ -1,5 +1,132 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "aho-corasick"
+version = "0.7.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7404febffaa47dac81aa44dba71523c9d069b1bdc50a77db41195149e17f68e5"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "bare-metal"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5deb64efa5bd81e31fcd1938615a6d98c82eafcbcd787162b6f63b91d6bac5b3"
+dependencies = [
+ "rustc_version",
+]
+
+[[package]]
+name = "bit_field"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dcb6dd1c2376d2e096796e234a70e17e94cc2d5d54ff8ce42b28cef1d0d359a4"
+
+[[package]]
+name = "bitflags"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
+
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+dependencies = [
+ "spin",
+]
+
+[[package]]
+name = "memchr"
+version = "2.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ee1c47aaa256ecabcaea351eae4a9b01ef39ed810004e298d2511ed284b1525"
+
 [[package]]
 name = "os"
 version = "0.1.0"
+dependencies = [
+ "lazy_static",
+ "riscv",
+]
+
+[[package]]
+name = "regex"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38cf2c13ed4745de91a5eb834e11c00bcc3709e773173b2ce4c56c9fbde04b9c"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+ "thread_local",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.6.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3b181ba2dcf07aaccad5448e8ead58db5b742cf85dfe035e2227f137a539a189"
+
+[[package]]
+name = "riscv"
+version = "0.6.0"
+source = "git+https://github.com/rcore-os/riscv#21e32ee1dc786cc0d5006ceee0040ce4f8398575"
+dependencies = [
+ "bare-metal",
+ "bit_field",
+ "bitflags",
+ "riscv-target",
+]
+
+[[package]]
+name = "riscv-target"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "88aa938cda42a0cf62a20cfe8d139ff1af20c2e681212b5b34adb5a58333f222"
+dependencies = [
+ "lazy_static",
+ "regex",
+]
+
+[[package]]
+name = "rustc_version"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
+dependencies = [
+ "semver",
+]
+
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
+dependencies = [
+ "semver-parser",
+]
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
+
+[[package]]
+name = "spin"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
+
+[[package]]
+name = "thread_local"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d40c6d1b69745a6ec6fb1ca717914848da4b44ae29d9b3080cbee91d72a69b14"
+dependencies = [
+ "lazy_static",
+]
diff --git a/os/Cargo.toml b/os/Cargo.toml
index b6770dc1..43768d78 100644
--- a/os/Cargo.toml
+++ b/os/Cargo.toml
@@ -7,3 +7,5 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+riscv = { git = "https://github.com/rcore-os/riscv", features = ["inline-asm"] }
+lazy_static = { version = "1.4.0", features = ["spin_no_std"] }
\ No newline at end of file
diff --git a/os/build.rs b/os/build.rs
index a358a266..3794b21a 100644
--- a/os/build.rs
+++ b/os/build.rs
@@ -37,7 +37,8 @@ _num_app:
     .quad app_{}_end
     "#, apps.len() - 1)?;
 
-    for (idx, app_with_extension) in apps.iter().enumerate() {
+    for (idx, app) in apps.iter().enumerate() {
+        println!("app_{}: {}", idx, app);
         writeln!(f, r#"
     .section .data
     .global app_{0}_start
@@ -45,7 +46,7 @@ _num_app:
 app_{0}_start:
     .incbin "{2}{1}.bin"
 app_{0}_end:
-        "#, idx, app_with_extension, TARGET_PATH)?;
+        "#, idx, app, TARGET_PATH)?;
     }
     Ok(())
 }
\ No newline at end of file
diff --git a/os/src/batch.rs b/os/src/batch.rs
new file mode 100644
index 00000000..567b4b30
--- /dev/null
+++ b/os/src/batch.rs
@@ -0,0 +1,117 @@
+use core::cell::RefCell;
+use lazy_static::*;
+use crate::trap::TrapContext;
+
+const USER_STACK_SIZE: usize = 4096 * 2;
+const KERNEL_STACK_SIZE: usize = 4096 * 2;
+const MAX_APP_NUM: usize = 16;
+const APP_BASE_ADDRESS: usize = 0x80040000;
+const APP_SIZE_LIMIT: usize = 0x20000;
+
+#[repr(align(4096))]
+struct KernelStack {
+    data: [u8; KERNEL_STACK_SIZE],
+}
+
+#[repr(align(4096))]
+struct UserStack {
+    data: [u8; USER_STACK_SIZE],
+}
+
+static KERNEL_STACK: KernelStack = KernelStack { data: [0; KERNEL_STACK_SIZE] };
+static USER_STACK: UserStack = UserStack { data: [0; USER_STACK_SIZE] };
+
+impl KernelStack {
+    fn get_sp(&self) -> usize {
+        self.data.as_ptr() as usize + KERNEL_STACK_SIZE
+    }
+    pub fn push_context(&self, cx: TrapContext) -> &'static mut TrapContext {
+        let cx_ptr = (self.get_sp() - core::mem::size_of::<TrapContext>()) as *mut TrapContext;
+        unsafe { *cx_ptr = cx; }
+        unsafe { cx_ptr.as_mut().unwrap() }
+    }
+}
+
+impl UserStack {
+    fn get_sp(&self) -> usize {
+        self.data.as_ptr() as usize + USER_STACK_SIZE
+    }
+}
+
+struct AppManager {
+    inner: RefCell<AppManagerInner>,
+}
+struct AppManagerInner {
+    num_app: usize,
+    next_app: usize,
+    app_start: [usize; MAX_APP_NUM + 1],
+}
+unsafe impl Sync for AppManager {}
+
+impl AppManagerInner {
+    pub fn print_app_info(&self) {
+        println!("num_app = {}", self.num_app);
+        for i in 0..self.num_app {
+            println!("app_{} [{:#x}, {:#x})", i, self.app_start[i], self.app_start[i + 1]);
+        }
+    }
+
+    unsafe fn load_app(&self, app_id: usize) {
+        // clear app area
+        (APP_BASE_ADDRESS..APP_BASE_ADDRESS + APP_SIZE_LIMIT).for_each(|addr| {
+            (addr as *mut u8).write_volatile(0);
+        });
+        let app_src = core::slice::from_raw_parts(
+            self.app_start[app_id] as *const u8,
+            self.app_start[app_id + 1] - self.app_start[app_id]
+        );
+        let app_dst = core::slice::from_raw_parts_mut(
+            APP_BASE_ADDRESS as *mut u8,
+            app_src.len()
+        );
+        app_dst.copy_from_slice(app_src);
+    }
+
+    pub fn run_next_app(&mut self) {
+        unsafe { self.load_app(self.next_app); }
+        self.next_app += 1;
+        extern "C" { fn __restore(cx: &mut TrapContext); }
+        unsafe {
+            __restore(KERNEL_STACK.push_context(
+                TrapContext::app_init_context(APP_BASE_ADDRESS, USER_STACK.get_sp())
+            ));
+        }
+    }
+}
+
+lazy_static! {
+    static ref APP_MANAGER: AppManager = AppManager {
+        inner: RefCell::new({
+            extern "C" { fn _num_app(); }
+            let num_app_ptr = _num_app as usize as *const usize;
+            let num_app = unsafe { num_app_ptr.read_volatile() };
+            let mut app_start: [usize; MAX_APP_NUM + 1] = [0; MAX_APP_NUM + 1];
+            let app_start_raw: &[usize] = unsafe {
+                core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1)
+            };
+            &app_start[..=num_app].copy_from_slice(app_start_raw);
+            AppManagerInner {
+                num_app,
+                next_app: 0,
+                app_start,
+            }
+        }),
+    };
+}
+
+pub fn init() {
+    print_app_info();
+}
+
+pub fn print_app_info() {
+    APP_MANAGER.inner.borrow().print_app_info();
+}
+
+pub fn run_next_app() {
+    APP_MANAGER.inner.borrow_mut().run_next_app();
+}
diff --git a/os/src/main.rs b/os/src/main.rs
index d571e81f..67b32312 100644
--- a/os/src/main.rs
+++ b/os/src/main.rs
@@ -10,6 +10,7 @@ mod lang_items;
 mod sbi;
 mod syscall;
 mod trap;
+mod batch;
 
 global_asm!(include_str!("entry.asm"));
 global_asm!(include_str!("link_app.S"));
@@ -28,17 +29,7 @@ fn clear_bss() {
 pub fn rust_main() -> ! {
     clear_bss();
     println!("Hello, world!");
-    extern "C" {
-        fn _num_app();
-    }
-    let num_app_ptr = _num_app as usize as *const usize;
-    let num_app = unsafe { num_app_ptr.read_volatile() };
-    println!("num_app = {}", num_app);
-    let app_start: &[usize] = unsafe {
-        core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1)
-    };
-    for i in 0..num_app {
-        println!("app_{} [{:#x}, {:#x})", i, app_start[i], app_start[i + 1]);
-    }
+    batch::init();
+    batch::run_next_app();
     panic!("Shutdown machine!");
 }
\ No newline at end of file
diff --git a/os/src/trap.rs b/os/src/trap.rs
deleted file mode 100644
index e69de29b..00000000
diff --git a/os/src/trap/context.rs b/os/src/trap/context.rs
new file mode 100644
index 00000000..b4245227
--- /dev/null
+++ b/os/src/trap/context.rs
@@ -0,0 +1,23 @@
+use riscv::register::sstatus::{Sstatus, self, SPP};
+
+#[repr(C)]
+pub struct TrapContext {
+    x: [usize; 32],
+    sstatus: Sstatus,
+    sepc: usize,
+}
+
+impl TrapContext {
+    pub fn set_sp(&mut self, sp: usize) { self.x[2] = sp; }
+    pub fn app_init_context(entry: usize, sp: usize) -> Self {
+        let mut sstatus = sstatus::read();
+        sstatus.set_spp(SPP::User);
+        let mut cx = Self {
+            x: [0; 32],
+            sstatus,
+            sepc: entry,
+        };
+        cx.set_sp(sp);
+        cx
+    }
+}
diff --git a/os/src/trap/mod.rs b/os/src/trap/mod.rs
new file mode 100644
index 00000000..2d7db829
--- /dev/null
+++ b/os/src/trap/mod.rs
@@ -0,0 +1,38 @@
+mod context;
+
+use riscv::register::{
+    mtvec::TrapMode,
+    stvec,
+    scause::{
+        self,
+        Trap,
+        Exception,
+    },
+    stval,
+};
+
+global_asm!(include_str!("trap.S"));
+
+pub fn init() {
+    extern "C" { fn __alltraps(); }
+    unsafe {
+        stvec::write(__alltraps as usize, TrapMode::Direct);
+    }
+}
+
+#[no_mangle]
+pub fn trap_handler(cx: &mut TrapContext) -> &mut TrapContext {
+    let scause = scause::read();
+    let stval = stval::read();
+    match scause.cause() {
+        Trap::Exception(Exception::UserEnvCall) => {
+            panic!("Triggered UserEnvCall!");
+        }
+        _ => {
+            panic!("Unsupported trap!");
+        }
+    }
+    cx
+}
+
+pub use context::TrapContext;
\ No newline at end of file
diff --git a/os/src/trap/trap.S b/os/src/trap/trap.S
new file mode 100644
index 00000000..9d6967cb
--- /dev/null
+++ b/os/src/trap/trap.S
@@ -0,0 +1,64 @@
+.altmacro
+.macro SAVE_GP n
+    sd x\n, \n*8(sp)
+.endm
+.macro LOAD_GP n
+    ld x\n, \n*8(sp)
+.endm
+    .section .text
+    .globl __alltraps
+    .globl __restore
+    .align 2
+__alltraps:
+    csrrw sp, sscratch, sp
+    # now sp->kernel stack, sscratch->user stack
+    # allocate a TrapContext on kernel stack
+    addi sp, sp, -34*8
+    # save general-purpose registers
+    sd x1, 1*8(sp)
+    # skip sp(x2), we will save it later
+    sd x3, 3*8(sp)
+    # skip tp(x4), application does not use it
+    # save x5~x31
+    .set n, 5
+    .rept 27
+        SAVE_GP %n
+        .set n, n+1
+    .endr
+    # we can use t0/t1/t2 freely, because they were saved on kernel stack
+    csrr t0, sstatus
+    csrr t1, sepc
+    sd t0, 32*8(sp)
+    sd t1, 33*8(sp)
+    # read user stack from sscratch and save it on the kernel stack
+    csrr t2, sscratch
+    sd t2, 2*8(sp)
+    # set input argument of trap_handler(cx: &mut TrapContext)
+    mv a0, sp
+    call trap_handler
+
+__restore:
+    # case1: start running app by __restore
+    # case2: back to U after handling trap
+    mv sp, a0
+    # now sp->kernel stack(after allocated), sscratch->user stack
+    # restore sstatus/sepc
+    ld t0, 32*8(sp)
+    ld t1, 33*8(sp)
+    ld t2, 2*8(sp)
+    csrw sstatus, t0
+    csrw sepc, t1
+    csrw sscratch, t2
+    # restore general-purpuse registers except sp/tp
+    ld x1, 1*8(sp)
+    ld x3, 3*8(sp)
+    .set n, 5
+    .rept 27
+        LOAD_GP %n
+        .set n, n+1
+    .endr
+    # release TrapContext on kernel stack
+    addi sp, sp, 34*8
+    # now sp->kernel stack, sscratch->user stack
+    csrrw sp, sscratch, sp
+    sret
diff --git a/user/src/lib.rs b/user/src/lib.rs
index 0a6eb264..c905e412 100644
--- a/user/src/lib.rs
+++ b/user/src/lib.rs
@@ -11,8 +11,8 @@ mod lang_items;
 #[no_mangle]
 #[link_section = ".text.entry"]
 pub extern "C" fn _start() -> ! {
-    main();
-    loop {}
+    syscall::sys_exit(main());
+    panic!("unreachable after sys_exit!");
 }
 
 #[linkage = "weak"]
diff --git a/user/src/syscall.rs b/user/src/syscall.rs
index fbd743ea..edb26d77 100644
--- a/user/src/syscall.rs
+++ b/user/src/syscall.rs
@@ -1,6 +1,7 @@
 pub const STDOUT: usize = 1;
 
 const SYSCALL_WRITE: usize = 64;
+const SYSCALL_EXIT: usize = 93;
 
 fn syscall(id: usize, args: [usize; 3]) -> isize {
     let mut ret: isize;
@@ -17,4 +18,8 @@ fn syscall(id: usize, args: [usize; 3]) -> isize {
 
 pub fn sys_write(fd: usize, buffer: &[u8]) -> isize {
     syscall(SYSCALL_WRITE, [fd, buffer.as_ptr() as usize, buffer.len()])
-}
\ No newline at end of file
+}
+
+pub fn sys_exit(xstate: i32) -> isize {
+    syscall(SYSCALL_EXIT, [xstate as usize, 0, 0])
+}