diff --git a/easy-fs/src/bitmap.rs b/easy-fs/src/bitmap.rs
index 2cea613e..287e8486 100644
--- a/easy-fs/src/bitmap.rs
+++ b/easy-fs/src/bitmap.rs
@@ -1,16 +1,16 @@
 use super::{get_block_cache, BlockDevice, BLOCK_SZ};
 use alloc::sync::Arc;
-
+/// A bitmap block
 type BitmapBlock = [u64; 64];
-
+/// Number of bits in a block
 const BLOCK_BITS: usize = BLOCK_SZ * 8;
-
+/// A bitmap
 pub struct Bitmap {
     start_block_id: usize,
     blocks: usize,
 }
 
-/// Return (block_pos, bits64_pos, inner_pos)
+/// Decompose bits into (block_pos, bits64_pos, inner_pos)
 fn decomposition(mut bit: usize) -> (usize, usize, usize) {
     let block_pos = bit / BLOCK_BITS;
     bit %= BLOCK_BITS;
@@ -18,13 +18,14 @@ fn decomposition(mut bit: usize) -> (usize, usize, usize) {
 }
 
 impl Bitmap {
+    /// A new bitmap from start block id and number of blocks
     pub fn new(start_block_id: usize, blocks: usize) -> Self {
         Self {
             start_block_id,
             blocks,
         }
     }
-
+    /// Allocate a new block from a block device
     pub fn alloc(&self, block_device: &Arc<dyn BlockDevice>) -> Option<usize> {
         for block_id in 0..self.blocks {
             let pos = get_block_cache(
@@ -52,7 +53,7 @@ impl Bitmap {
         }
         None
     }
-
+    /// Deallocate a block
     pub fn dealloc(&self, block_device: &Arc<dyn BlockDevice>, bit: usize) {
         let (block_pos, bits64_pos, inner_pos) = decomposition(bit);
         get_block_cache(block_pos + self.start_block_id, Arc::clone(block_device))
@@ -62,7 +63,7 @@ impl Bitmap {
                 bitmap_block[bits64_pos] -= 1u64 << inner_pos;
             });
     }
-
+    /// Get the max number of allocatable blocks
     pub fn maximum(&self) -> usize {
         self.blocks * BLOCK_BITS
     }
diff --git a/easy-fs/src/block_cache.rs b/easy-fs/src/block_cache.rs
index 4b90294a..c9bfa262 100644
--- a/easy-fs/src/block_cache.rs
+++ b/easy-fs/src/block_cache.rs
@@ -3,11 +3,15 @@ use alloc::collections::VecDeque;
 use alloc::sync::Arc;
 use lazy_static::*;
 use spin::Mutex;
-
+/// Cached block inside memory
 pub struct BlockCache {
+    /// cached block data
     cache: [u8; BLOCK_SZ],
+    /// underlying block id
     block_id: usize,
+    /// underlying block device
     block_device: Arc<dyn BlockDevice>,
+    /// whether the block is dirty
     modified: bool,
 }
 
@@ -23,7 +27,7 @@ impl BlockCache {
             modified: false,
         }
     }
-
+    /// Get the address of an offset inside the cached block data
     fn addr_of_offset(&self, offset: usize) -> usize {
         &self.cache[offset] as *const _ as usize
     }
@@ -70,7 +74,7 @@ impl Drop for BlockCache {
         self.sync()
     }
 }
-
+/// Use a block cache of 16 blocks
 const BLOCK_CACHE_SIZE: usize = 16;
 
 pub struct BlockCacheManager {
@@ -118,10 +122,11 @@ impl BlockCacheManager {
 }
 
 lazy_static! {
+    /// The global block cache manager
     pub static ref BLOCK_CACHE_MANAGER: Mutex<BlockCacheManager> =
         Mutex::new(BlockCacheManager::new());
 }
-
+/// Get the block cache corresponding to the given block id and block device
 pub fn get_block_cache(
     block_id: usize,
     block_device: Arc<dyn BlockDevice>,
@@ -130,7 +135,7 @@ pub fn get_block_cache(
         .lock()
         .get_block_cache(block_id, block_device)
 }
-
+/// Sync all block cache to block device
 pub fn block_cache_sync_all() {
     let manager = BLOCK_CACHE_MANAGER.lock();
     for (_, cache) in manager.queue.iter() {
diff --git a/easy-fs/src/block_dev.rs b/easy-fs/src/block_dev.rs
index 8a01eddb..555954a6 100644
--- a/easy-fs/src/block_dev.rs
+++ b/easy-fs/src/block_dev.rs
@@ -1,6 +1,9 @@
 use core::any::Any;
-
+/// Trait for block devices
+/// which reads and writes data in the unit of blocks
 pub trait BlockDevice: Send + Sync + Any {
+    ///Read data form block to buffer
     fn read_block(&self, block_id: usize, buf: &mut [u8]);
+    ///Write data from buffer to block
     fn write_block(&self, block_id: usize, buf: &[u8]);
 }
diff --git a/easy-fs/src/efs.rs b/easy-fs/src/efs.rs
index 82e95ae0..202b9eb9 100644
--- a/easy-fs/src/efs.rs
+++ b/easy-fs/src/efs.rs
@@ -5,18 +5,22 @@ use super::{
 use crate::BLOCK_SZ;
 use alloc::sync::Arc;
 use spin::Mutex;
-
+///An easy file system on block
 pub struct EasyFileSystem {
+    ///Real device
     pub block_device: Arc<dyn BlockDevice>,
+    ///Inode bitmap
     pub inode_bitmap: Bitmap,
+    ///Data bitmap
     pub data_bitmap: Bitmap,
     inode_area_start_block: u32,
     data_area_start_block: u32,
 }
 
 type DataBlock = [u8; BLOCK_SZ];
-
+/// An easy fs over a block device
 impl EasyFileSystem {
+    /// A data block of block size
     pub fn create(
         block_device: Arc<dyn BlockDevice>,
         total_blocks: u32,
@@ -77,7 +81,7 @@ impl EasyFileSystem {
         block_cache_sync_all();
         Arc::new(Mutex::new(efs))
     }
-
+    /// Open a block device as a filesystem
     pub fn open(block_device: Arc<dyn BlockDevice>) -> Arc<Mutex<Self>> {
         // read SuperBlock
         get_block_cache(0, Arc::clone(&block_device))
@@ -99,7 +103,7 @@ impl EasyFileSystem {
                 Arc::new(Mutex::new(efs))
             })
     }
-
+    /// Get the root inode of the filesystem
     pub fn root_inode(efs: &Arc<Mutex<Self>>) -> Inode {
         let block_device = Arc::clone(&efs.lock().block_device);
         // acquire efs lock temporarily
@@ -107,7 +111,7 @@ impl EasyFileSystem {
         // release efs lock
         Inode::new(block_id, block_offset, Arc::clone(efs), block_device)
     }
-
+    /// Get inode by id
     pub fn get_disk_inode_pos(&self, inode_id: u32) -> (u32, usize) {
         let inode_size = core::mem::size_of::<DiskInode>();
         let inodes_per_block = (BLOCK_SZ / inode_size) as u32;
@@ -117,20 +121,20 @@ impl EasyFileSystem {
             (inode_id % inodes_per_block) as usize * inode_size,
         )
     }
-
+    /// Get data block by id
     pub fn get_data_block_id(&self, data_block_id: u32) -> u32 {
         self.data_area_start_block + data_block_id
     }
-
+    /// Allocate a new inode
     pub fn alloc_inode(&mut self) -> u32 {
         self.inode_bitmap.alloc(&self.block_device).unwrap() as u32
     }
 
-    /// Return a block ID not ID in the data area.
+    /// Allocate a data block
     pub fn alloc_data(&mut self) -> u32 {
         self.data_bitmap.alloc(&self.block_device).unwrap() as u32 + self.data_area_start_block
     }
-
+    /// Deallocate a data block
     pub fn dealloc_data(&mut self, block_id: u32) {
         get_block_cache(block_id as usize, Arc::clone(&self.block_device))
             .lock()
diff --git a/easy-fs/src/layout.rs b/easy-fs/src/layout.rs
index 618484cf..6daccaf7 100644
--- a/easy-fs/src/layout.rs
+++ b/easy-fs/src/layout.rs
@@ -3,16 +3,24 @@ use alloc::sync::Arc;
 use alloc::vec::Vec;
 use core::fmt::{Debug, Formatter, Result};
 
+/// Magic number for sanity check
 const EFS_MAGIC: u32 = 0x3b800001;
+/// The max number of direct inodes
 const INODE_DIRECT_COUNT: usize = 28;
+/// The max length of inode name
 const NAME_LENGTH_LIMIT: usize = 27;
+/// The max number of indirect1 inodes
 const INODE_INDIRECT1_COUNT: usize = BLOCK_SZ / 4;
+/// The max number of indirect2 inodes
 const INODE_INDIRECT2_COUNT: usize = INODE_INDIRECT1_COUNT * INODE_INDIRECT1_COUNT;
+/// The upper bound of direct inode index
 const DIRECT_BOUND: usize = INODE_DIRECT_COUNT;
+/// The upper bound of indirect1 inode index
 const INDIRECT1_BOUND: usize = DIRECT_BOUND + INODE_INDIRECT1_COUNT;
+/// The upper bound of indirect2 inode indexs
 #[allow(unused)]
 const INDIRECT2_BOUND: usize = INDIRECT1_BOUND + INODE_INDIRECT2_COUNT;
-
+/// Super block of a filesystem
 #[repr(C)]
 pub struct SuperBlock {
     magic: u32,
@@ -36,6 +44,7 @@ impl Debug for SuperBlock {
 }
 
 impl SuperBlock {
+    /// Initialize a super block
     pub fn initialize(
         &mut self,
         total_blocks: u32,
@@ -53,20 +62,23 @@ impl SuperBlock {
             data_area_blocks,
         }
     }
+    /// Check if a super block is valid using efs magic
     pub fn is_valid(&self) -> bool {
         self.magic == EFS_MAGIC
     }
 }
-
+/// Type of a disk inode
 #[derive(PartialEq)]
 pub enum DiskInodeType {
     File,
     Directory,
 }
 
+/// A indirect block
 type IndirectBlock = [u32; BLOCK_SZ / 4];
+/// A data block
 type DataBlock = [u8; BLOCK_SZ];
-
+/// A disk inode
 #[repr(C)]
 pub struct DiskInode {
     pub size: u32,
@@ -77,7 +89,8 @@ pub struct DiskInode {
 }
 
 impl DiskInode {
-    /// indirect1 and indirect2 block are allocated only when they are needed.
+    /// Initialize a disk inode, as well as all direct inodes under it
+    /// indirect1 and indirect2 block are allocated only when they are needed
     pub fn initialize(&mut self, type_: DiskInodeType) {
         self.size = 0;
         self.direct.iter_mut().for_each(|v| *v = 0);
@@ -85,9 +98,11 @@ impl DiskInode {
         self.indirect2 = 0;
         self.type_ = type_;
     }
+    /// Whether this inode is a directory
     pub fn is_dir(&self) -> bool {
         self.type_ == DiskInodeType::Directory
     }
+    /// Whether this inode is a file
     #[allow(unused)]
     pub fn is_file(&self) -> bool {
         self.type_ == DiskInodeType::File
@@ -116,10 +131,12 @@ impl DiskInode {
         }
         total as u32
     }
+    /// Get the number of data blocks that have to be allocated given the new size of data
     pub fn blocks_num_needed(&self, new_size: u32) -> u32 {
         assert!(new_size >= self.size);
         Self::total_blocks(new_size) - Self::total_blocks(self.size)
     }
+    /// Get id of block given inner id
     pub fn get_block_id(&self, inner_id: u32, block_device: &Arc<dyn BlockDevice>) -> u32 {
         let inner_id = inner_id as usize;
         if inner_id < INODE_DIRECT_COUNT {
@@ -144,6 +161,7 @@ impl DiskInode {
                 })
         }
     }
+    /// Inncrease the size of current disk inode
     pub fn increase_size(
         &mut self,
         new_size: u32,
@@ -218,7 +236,6 @@ impl DiskInode {
     }
 
     /// Clear size to zero and return blocks that should be deallocated.
-    ///
     /// We will clear the block contents to zero later.
     pub fn clear_size(&mut self, block_device: &Arc<dyn BlockDevice>) -> Vec<u32> {
         let mut v: Vec<u32> = Vec::new();
@@ -291,6 +308,7 @@ impl DiskInode {
         self.indirect2 = 0;
         v
     }
+    /// Read data from current disk inode
     pub fn read_at(
         &self,
         offset: usize,
@@ -330,7 +348,8 @@ impl DiskInode {
         }
         read_size
     }
-    /// File size must be adjusted before.
+    /// Write data into current disk inode
+    /// size must be adjusted properly beforehand
     pub fn write_at(
         &mut self,
         offset: usize,
@@ -369,22 +388,24 @@ impl DiskInode {
         write_size
     }
 }
-
+/// A directory entry
 #[repr(C)]
 pub struct DirEntry {
     name: [u8; NAME_LENGTH_LIMIT + 1],
     inode_number: u32,
 }
-
+/// Size of a directory entry
 pub const DIRENT_SZ: usize = 32;
 
 impl DirEntry {
+    /// Create an empty directory entry
     pub fn empty() -> Self {
         Self {
             name: [0u8; NAME_LENGTH_LIMIT + 1],
             inode_number: 0,
         }
     }
+    /// Crate a directory entry from name and inode number
     pub fn new(name: &str, inode_number: u32) -> Self {
         let mut bytes = [0u8; NAME_LENGTH_LIMIT + 1];
         bytes[..name.len()].copy_from_slice(name.as_bytes());
@@ -393,16 +414,20 @@ impl DirEntry {
             inode_number,
         }
     }
+    /// Serialize into bytes
     pub fn as_bytes(&self) -> &[u8] {
         unsafe { core::slice::from_raw_parts(self as *const _ as usize as *const u8, DIRENT_SZ) }
     }
+    /// Serialize into mutable bytes
     pub fn as_bytes_mut(&mut self) -> &mut [u8] {
         unsafe { core::slice::from_raw_parts_mut(self as *mut _ as usize as *mut u8, DIRENT_SZ) }
     }
+    /// Get name of the entry
     pub fn name(&self) -> &str {
         let len = (0usize..).find(|i| self.name[*i] == 0).unwrap();
         core::str::from_utf8(&self.name[..len]).unwrap()
     }
+    /// Get inode number of the entry
     pub fn inode_number(&self) -> u32 {
         self.inode_number
     }
diff --git a/easy-fs/src/lib.rs b/easy-fs/src/lib.rs
index fa36e6b7..822c237e 100644
--- a/easy-fs/src/lib.rs
+++ b/easy-fs/src/lib.rs
@@ -1,14 +1,14 @@
+//!An easy file system isolated from the kernel
 #![no_std]
-
+#![deny(missing_docs)]
 extern crate alloc;
-
 mod bitmap;
 mod block_cache;
 mod block_dev;
 mod efs;
 mod layout;
 mod vfs;
-
+/// Use a block size of 512 bytes
 pub const BLOCK_SZ: usize = 512;
 use bitmap::Bitmap;
 use block_cache::{block_cache_sync_all, get_block_cache};
diff --git a/easy-fs/src/vfs.rs b/easy-fs/src/vfs.rs
index d67948f5..9f90c50d 100644
--- a/easy-fs/src/vfs.rs
+++ b/easy-fs/src/vfs.rs
@@ -6,7 +6,7 @@ use alloc::string::String;
 use alloc::sync::Arc;
 use alloc::vec::Vec;
 use spin::{Mutex, MutexGuard};
-
+/// Virtual filesystem layer over easy-fs
 pub struct Inode {
     block_id: usize,
     block_offset: usize,
@@ -15,7 +15,7 @@ pub struct Inode {
 }
 
 impl Inode {
-    /// We should not acquire efs lock here.
+    /// Create a vfs inode
     pub fn new(
         block_id: u32,
         block_offset: usize,
@@ -29,19 +29,19 @@ impl Inode {
             block_device,
         }
     }
-
+    /// Call a function over a disk inode to read it
     fn read_disk_inode<V>(&self, f: impl FnOnce(&DiskInode) -> V) -> V {
         get_block_cache(self.block_id, Arc::clone(&self.block_device))
             .lock()
             .read(self.block_offset, f)
     }
-
+    /// Call a function over a disk inode to modify it
     fn modify_disk_inode<V>(&self, f: impl FnOnce(&mut DiskInode) -> V) -> V {
         get_block_cache(self.block_id, Arc::clone(&self.block_device))
             .lock()
             .modify(self.block_offset, f)
     }
-
+    /// Find inode under a disk inode by name
     fn find_inode_id(&self, name: &str, disk_inode: &DiskInode) -> Option<u32> {
         // assert it is a directory
         assert!(disk_inode.is_dir());
@@ -58,7 +58,7 @@ impl Inode {
         }
         None
     }
-
+    /// Find inode under current inode by name
     pub fn find(&self, name: &str) -> Option<Arc<Inode>> {
         let fs = self.fs.lock();
         self.read_disk_inode(|disk_inode| {
@@ -73,7 +73,7 @@ impl Inode {
             })
         })
     }
-
+    /// Increase the size of a disk inode
     fn increase_size(
         &self,
         new_size: u32,
@@ -90,7 +90,7 @@ impl Inode {
         }
         disk_inode.increase_size(new_size, v, &self.block_device);
     }
-
+    /// Create inode under current inode by name
     pub fn create(&self, name: &str) -> Option<Arc<Inode>> {
         let mut fs = self.fs.lock();
         let op = |root_inode: &DiskInode| {
@@ -138,7 +138,7 @@ impl Inode {
         )))
         // release efs lock automatically by compiler
     }
-
+    /// List inodes under current inode
     pub fn ls(&self) -> Vec<String> {
         let _fs = self.fs.lock();
         self.read_disk_inode(|disk_inode| {
@@ -155,12 +155,12 @@ impl Inode {
             v
         })
     }
-
+    /// Read data from current inode
     pub fn read_at(&self, offset: usize, buf: &mut [u8]) -> usize {
         let _fs = self.fs.lock();
         self.read_disk_inode(|disk_inode| disk_inode.read_at(offset, buf, &self.block_device))
     }
-
+    /// Write data to current inode
     pub fn write_at(&self, offset: usize, buf: &[u8]) -> usize {
         let mut fs = self.fs.lock();
         let size = self.modify_disk_inode(|disk_inode| {
@@ -170,7 +170,7 @@ impl Inode {
         block_cache_sync_all();
         size
     }
-
+    /// Clear the data in current inode
     pub fn clear(&self) {
         let mut fs = self.fs.lock();
         self.modify_disk_inode(|disk_inode| {
diff --git a/os/src/config.rs b/os/src/config.rs
index e7adf538..3e349ecc 100644
--- a/os/src/config.rs
+++ b/os/src/config.rs
@@ -1,3 +1,4 @@
+//! Constants used in rCore
 #[allow(unused)]
 
 pub const USER_STACK_SIZE: usize = 4096 * 2;
diff --git a/os/src/console.rs b/os/src/console.rs
index dda4911a..5435310b 100644
--- a/os/src/console.rs
+++ b/os/src/console.rs
@@ -1,3 +1,4 @@
+//! SBI console driver, for text output
 use crate::sbi::console_putchar;
 use core::fmt::{self, Write};
 
@@ -17,6 +18,7 @@ pub fn print(args: fmt::Arguments) {
 }
 
 #[macro_export]
+/// print string macro
 macro_rules! print {
     ($fmt: literal $(, $($arg: tt)+)?) => {
         $crate::console::print(format_args!($fmt $(, $($arg)+)?));
@@ -24,6 +26,7 @@ macro_rules! print {
 }
 
 #[macro_export]
+/// println string macro
 macro_rules! println {
     ($fmt: literal $(, $($arg: tt)+)?) => {
         $crate::console::print(format_args!(concat!($fmt, "\n") $(, $($arg)+)?));
diff --git a/os/src/fs/inode.rs b/os/src/fs/inode.rs
index ad22ca58..89f957f7 100644
--- a/os/src/fs/inode.rs
+++ b/os/src/fs/inode.rs
@@ -1,3 +1,9 @@
+//! `Arc<Inode>` -> `OSInodeInner`: In order to open files concurrently 
+//! we need to wrap `Inode` into `Arc`,but `Mutex` in `Inode` prevents 
+//! file systems from being accessed simultaneously 
+//! 
+//! `UPSafeCell<OSInodeInner>` -> `OSInode`: for static `ROOT_INODE`,we 
+//! need to wrap `OSInodeInner` into `UPSafeCell`
 use super::File;
 use crate::drivers::BLOCK_DEVICE;
 use crate::mm::UserBuffer;
@@ -7,19 +13,21 @@ use alloc::vec::Vec;
 use bitflags::*;
 use easy_fs::{EasyFileSystem, Inode};
 use lazy_static::*;
-
+/// A wrapper around a filesystem inode
+/// to implement File trait atop 
 pub struct OSInode {
     readable: bool,
     writable: bool,
     inner: UPSafeCell<OSInodeInner>,
 }
-
+/// The OS inode inner in 'UPSafeCell'
 pub struct OSInodeInner {
     offset: usize,
     inode: Arc<Inode>,
 }
 
 impl OSInode {
+    /// Construct an OS inode from a inode
     pub fn new(readable: bool, writable: bool, inode: Arc<Inode>) -> Self {
         Self {
             readable,
@@ -27,6 +35,7 @@ impl OSInode {
             inner: unsafe { UPSafeCell::new(OSInodeInner { offset: 0, inode }) },
         }
     }
+    /// Read all data inside a inode into vector
     pub fn read_all(&self) -> Vec<u8> {
         let mut inner = self.inner.exclusive_access();
         let mut buffer = [0u8; 512];
@@ -49,7 +58,7 @@ lazy_static! {
         Arc::new(EasyFileSystem::root_inode(&efs))
     };
 }
-
+/// List all files in the filesystems
 pub fn list_apps() {
     println!("/**** APPS ****");
     for app in ROOT_INODE.ls() {
@@ -58,12 +67,18 @@ pub fn list_apps() {
     println!("**************/");
 }
 
-bitflags! {
+bitflags! {    
+    ///Open file flags
     pub struct OpenFlags: u32 {
+        ///Read only
         const RDONLY = 0;
+        ///Write only
         const WRONLY = 1 << 0;
+        ///Read & Write
         const RDWR = 1 << 1;
+        ///Allow create
         const CREATE = 1 << 9;
+        ///Clear file and return an empty one
         const TRUNC = 1 << 10;
     }
 }
@@ -81,7 +96,7 @@ impl OpenFlags {
         }
     }
 }
-
+///Open file with flags
 pub fn open_file(name: &str, flags: OpenFlags) -> Option<Arc<OSInode>> {
     let (readable, writable) = flags.read_write();
     if flags.contains(OpenFlags::CREATE) {
diff --git a/os/src/fs/mod.rs b/os/src/fs/mod.rs
index ce88f287..ab91cc1d 100644
--- a/os/src/fs/mod.rs
+++ b/os/src/fs/mod.rs
@@ -1,12 +1,17 @@
+//! File system in os
 mod inode;
 mod stdio;
 
 use crate::mm::UserBuffer;
-
+/// File trait 
 pub trait File: Send + Sync {
+    /// If readable
     fn readable(&self) -> bool;
+    /// If writable
     fn writable(&self) -> bool;
+    /// Read file to `UserBuffer`
     fn read(&self, buf: UserBuffer) -> usize;
+    /// Write `UserBuffer` to file
     fn write(&self, buf: UserBuffer) -> usize;
 }
 
diff --git a/os/src/fs/stdio.rs b/os/src/fs/stdio.rs
index 7c74d3e1..8375ac90 100644
--- a/os/src/fs/stdio.rs
+++ b/os/src/fs/stdio.rs
@@ -1,10 +1,11 @@
+//!Stdin & Stdout
 use super::File;
 use crate::mm::UserBuffer;
 use crate::sbi::console_getchar;
 use crate::task::suspend_current_and_run_next;
-
+///Standard input
 pub struct Stdin;
-
+///Standard output
 pub struct Stdout;
 
 impl File for Stdin {
diff --git a/os/src/lang_items.rs b/os/src/lang_items.rs
index af3e5152..49b16a2e 100644
--- a/os/src/lang_items.rs
+++ b/os/src/lang_items.rs
@@ -1,3 +1,4 @@
+//! The panic handler
 use crate::sbi::shutdown;
 use core::panic::PanicInfo;
 
diff --git a/os/src/main.rs b/os/src/main.rs
index cbc4ab40..85df7bc4 100644
--- a/os/src/main.rs
+++ b/os/src/main.rs
@@ -1,3 +1,25 @@
+//! The main module and entrypoint
+//!
+//! Various facilities of the kernels are implemented as submodules. The most
+//! important ones are:
+//!
+//! - [`trap`]: Handles all cases of switching from userspace to the kernel
+//! - [`task`]: Task management
+//! - [`syscall`]: System call handling and implementation
+//! - [`mm`]: Address map using SV39
+//! - [`sync`]: Wrap a static data structure inside it so that we are able to access it without any `unsafe`.
+//! - [`fs`]: Separate user from file system with some structures
+//! The operating system also starts in this module. Kernel code starts
+//! executing from `entry.asm`, after which [`rust_main()`] is called to
+//! initialize various pieces of functionality. (See its source code for
+//! details.)
+//!
+//! We then call [`task::run_tasks()`] and for the first time go to
+//! userspace.
+
+#![deny(missing_docs)]
+#![deny(warnings)]
+#![allow(unused_imports)]
 #![no_std]
 #![no_main]
 #![feature(panic_info_message)]
@@ -19,20 +41,20 @@ mod board;
 mod console;
 mod config;
 mod drivers;
-mod fs;
-mod lang_items;
-mod mm;
-mod sbi;
-mod sync;
-mod syscall;
-mod task;
-mod timer;
-mod trap;
+pub mod fs;
+pub mod lang_items;
+pub mod mm;
+pub mod sbi;
+pub mod sync;
+pub mod syscall;
+pub mod task;
+pub mod timer;
+pub mod trap;
 
 use core::arch::global_asm;
 
 global_asm!(include_str!("entry.asm"));
-
+/// clear BSS segment
 fn clear_bss() {
     extern "C" {
         fn sbss();
@@ -45,6 +67,7 @@ fn clear_bss() {
 }
 
 #[no_mangle]
+/// the rust entry-point of os
 pub fn rust_main() -> ! {
     clear_bss();
     println!("[kernel] Hello, world!");
diff --git a/os/src/mm/address.rs b/os/src/mm/address.rs
index dc5d08a8..2b7c5863 100644
--- a/os/src/mm/address.rs
+++ b/os/src/mm/address.rs
@@ -1,3 +1,4 @@
+//! Implementation of physical and virtual address and page number.
 use super::PageTableEntry;
 use crate::config::{PAGE_SIZE, PAGE_SIZE_BITS};
 use core::fmt::{self, Debug, Formatter};
@@ -14,14 +15,17 @@ pub struct PhysAddr(pub usize);
 
 #[repr(C)]
 #[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+///virtual address
 pub struct VirtAddr(pub usize);
 
 #[repr(C)]
 #[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+///phiscal page number
 pub struct PhysPageNum(pub usize);
 
 #[repr(C)]
 #[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+///virtual page number
 pub struct VirtPageNum(pub usize);
 
 /// Debugging
@@ -91,17 +95,21 @@ impl From<VirtPageNum> for usize {
         v.0
     }
 }
-
+///
 impl VirtAddr {
+    ///`VirtAddr`->`VirtPageNum`
     pub fn floor(&self) -> VirtPageNum {
         VirtPageNum(self.0 / PAGE_SIZE)
     }
+    ///`VirtAddr`->`VirtPageNum`
     pub fn ceil(&self) -> VirtPageNum {
         VirtPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
     }
+    ///Get page offset 
     pub fn page_offset(&self) -> usize {
         self.0 & (PAGE_SIZE - 1)
     }
+    ///Check page aligned 
     pub fn aligned(&self) -> bool {
         self.page_offset() == 0
     }
@@ -118,15 +126,19 @@ impl From<VirtPageNum> for VirtAddr {
     }
 }
 impl PhysAddr {
+    ///`PhysAddr`->`PhysPageNum`
     pub fn floor(&self) -> PhysPageNum {
         PhysPageNum(self.0 / PAGE_SIZE)
     }
+    ///`PhysAddr`->`PhysPageNum`
     pub fn ceil(&self) -> PhysPageNum {
         PhysPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
     }
+    ///Get page offset 
     pub fn page_offset(&self) -> usize {
         self.0 & (PAGE_SIZE - 1)
     }
+    ///Check page aligned 
     pub fn aligned(&self) -> bool {
         self.page_offset() == 0
     }
@@ -144,6 +156,7 @@ impl From<PhysPageNum> for PhysAddr {
 }
 
 impl VirtPageNum {
+    ///Return VPN 3 level index 
     pub fn indexes(&self) -> [usize; 3] {
         let mut vpn = self.0;
         let mut idx = [0usize; 3];
@@ -156,29 +169,35 @@ impl VirtPageNum {
 }
 
 impl PhysAddr {
+    ///Get reference to `PhysAddr` value 
     pub fn get_ref<T>(&self) -> &'static T {
         unsafe { (self.0 as *const T).as_ref().unwrap() }
     }
+    ///Get mutable reference to `PhysAddr` value 
     pub fn get_mut<T>(&self) -> &'static mut T {
         unsafe { (self.0 as *mut T).as_mut().unwrap() }
     }
 }
 impl PhysPageNum {
+    ///Get `PageTableEntry` on `PhysPageNum`
     pub fn get_pte_array(&self) -> &'static mut [PageTableEntry] {
         let pa: PhysAddr = (*self).into();
         unsafe { core::slice::from_raw_parts_mut(pa.0 as *mut PageTableEntry, 512) }
     }
+    ///Get u8 array on `PhysPageNum`
     pub fn get_bytes_array(&self) -> &'static mut [u8] {
         let pa: PhysAddr = (*self).into();
         unsafe { core::slice::from_raw_parts_mut(pa.0 as *mut u8, 4096) }
     }
+    ///Get Get mutable reference to `PhysAddr` value on `PhysPageNum`
     pub fn get_mut<T>(&self) -> &'static mut T {
         let pa: PhysAddr = (*self).into();
         pa.get_mut()
     }
 }
-
+///Add value by one
 pub trait StepByOne {
+    ///Add value by one
     fn step(&mut self);
 }
 impl StepByOne for VirtPageNum {
@@ -193,6 +212,7 @@ impl StepByOne for PhysPageNum {
 }
 
 #[derive(Copy, Clone)]
+/// a simple range structure for type T
 pub struct SimpleRange<T>
 where
     T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
@@ -225,6 +245,7 @@ where
         SimpleRangeIterator::new(self.l, self.r)
     }
 }
+/// iterator for the simple range structure
 pub struct SimpleRangeIterator<T>
 where
     T: StepByOne + Copy + PartialEq + PartialOrd + Debug,
@@ -255,4 +276,5 @@ where
         }
     }
 }
+/// a simple range structure for virtual page number
 pub type VPNRange = SimpleRange<VirtPageNum>;
diff --git a/os/src/mm/frame_allocator.rs b/os/src/mm/frame_allocator.rs
index 4bc7db26..ed398977 100644
--- a/os/src/mm/frame_allocator.rs
+++ b/os/src/mm/frame_allocator.rs
@@ -1,3 +1,5 @@
+//! Implementation of [`FrameAllocator`] which 
+//! controls all the frames in the operating system.
 use super::{PhysAddr, PhysPageNum};
 use crate::config::MEMORY_END;
 use crate::sync::UPSafeCell;
@@ -5,11 +7,14 @@ use alloc::vec::Vec;
 use core::fmt::{self, Debug, Formatter};
 use lazy_static::*;
 
+/// manage a frame which has the same lifecycle as the tracker
 pub struct FrameTracker {
+    ///
     pub ppn: PhysPageNum,
 }
 
 impl FrameTracker {
+    ///Create an empty `FrameTracker`
     pub fn new(ppn: PhysPageNum) -> Self {
         // page cleaning
         let bytes_array = ppn.get_bytes_array();
@@ -37,7 +42,7 @@ trait FrameAllocator {
     fn alloc(&mut self) -> Option<PhysPageNum>;
     fn dealloc(&mut self, ppn: PhysPageNum);
 }
-
+/// an implementation for frame allocator
 pub struct StackFrameAllocator {
     current: usize,
     end: usize,
@@ -83,10 +88,11 @@ impl FrameAllocator for StackFrameAllocator {
 type FrameAllocatorImpl = StackFrameAllocator;
 
 lazy_static! {
+    /// frame allocator instance through lazy_static!
     pub static ref FRAME_ALLOCATOR: UPSafeCell<FrameAllocatorImpl> =
         unsafe { UPSafeCell::new(FrameAllocatorImpl::new()) };
 }
-
+/// initiate the frame allocator using `ekernel` and `MEMORY_END`
 pub fn init_frame_allocator() {
     extern "C" {
         fn ekernel();
@@ -96,19 +102,20 @@ pub fn init_frame_allocator() {
         PhysAddr::from(MEMORY_END).floor(),
     );
 }
-
+/// allocate a frame
 pub fn frame_alloc() -> Option<FrameTracker> {
     FRAME_ALLOCATOR
         .exclusive_access()
         .alloc()
         .map(FrameTracker::new)
 }
-
+/// deallocate a frame
 pub fn frame_dealloc(ppn: PhysPageNum) {
     FRAME_ALLOCATOR.exclusive_access().dealloc(ppn);
 }
 
 #[allow(unused)]
+/// a simple test for frame allocator
 pub fn frame_allocator_test() {
     let mut v: Vec<FrameTracker> = Vec::new();
     for i in 0..5 {
diff --git a/os/src/mm/heap_allocator.rs b/os/src/mm/heap_allocator.rs
index 42a6d769..e5f8b304 100644
--- a/os/src/mm/heap_allocator.rs
+++ b/os/src/mm/heap_allocator.rs
@@ -1,16 +1,19 @@
+//! The global allocator
 use crate::config::KERNEL_HEAP_SIZE;
 use buddy_system_allocator::LockedHeap;
 
 #[global_allocator]
+/// heap allocator instance
 static HEAP_ALLOCATOR: LockedHeap = LockedHeap::empty();
 
 #[alloc_error_handler]
+/// panic when heap allocation error occurs
 pub fn handle_alloc_error(layout: core::alloc::Layout) -> ! {
     panic!("Heap allocation error, layout = {:?}", layout);
 }
-
+/// heap space ([u8; KERNEL_HEAP_SIZE])
 static mut HEAP_SPACE: [u8; KERNEL_HEAP_SIZE] = [0; KERNEL_HEAP_SIZE];
-
+/// initiate heap allocator
 pub fn init_heap() {
     unsafe {
         HEAP_ALLOCATOR
diff --git a/os/src/mm/memory_set.rs b/os/src/mm/memory_set.rs
index 8d97e848..9b28bfff 100644
--- a/os/src/mm/memory_set.rs
+++ b/os/src/mm/memory_set.rs
@@ -1,3 +1,4 @@
+//! Implementation of [`MapArea`] and [`MemorySet`].
 use super::{frame_alloc, FrameTracker};
 use super::{PTEFlags, PageTable, PageTableEntry};
 use super::{PhysAddr, PhysPageNum, VirtAddr, VirtPageNum};
@@ -25,26 +26,29 @@ extern "C" {
 }
 
 lazy_static! {
+    /// a memory set instance through lazy_static! managing kernel space
     pub static ref KERNEL_SPACE: Arc<UPSafeCell<MemorySet>> =
         Arc::new(unsafe { UPSafeCell::new(MemorySet::new_kernel()) });
 }
-
+///Get kernelspace root ppn
 pub fn kernel_token() -> usize {
     KERNEL_SPACE.exclusive_access().token()
 }
-
+/// memory set structure, controls virtual-memory space
 pub struct MemorySet {
     page_table: PageTable,
     areas: Vec<MapArea>,
 }
 
 impl MemorySet {
+    ///Create an empty `MemorySet`
     pub fn new_bare() -> Self {
         Self {
             page_table: PageTable::new(),
             areas: Vec::new(),
         }
     }
+    ///Get pagetable `root_ppn`
     pub fn token(&self) -> usize {
         self.page_table.token()
     }
@@ -60,6 +64,7 @@ impl MemorySet {
             None,
         );
     }
+    ///Remove `MapArea` that starts with `start_vpn`
     pub fn remove_area_with_start_vpn(&mut self, start_vpn: VirtPageNum) {
         if let Some((idx, area)) = self
             .areas
@@ -231,6 +236,7 @@ impl MemorySet {
             elf.header.pt2.entry_point() as usize,
         )
     }
+    ///Clone a same `MemorySet`
     pub fn from_existed_user(user_space: &MemorySet) -> MemorySet {
         let mut memory_set = Self::new_bare();
         // map trampoline
@@ -250,6 +256,7 @@ impl MemorySet {
         }
         memory_set
     }
+    ///Refresh TLB with `sfence.vma`
     pub fn activate(&self) {
         let satp = self.page_table.token();
         unsafe {
@@ -257,15 +264,17 @@ impl MemorySet {
             asm!("sfence.vma");
         }
     }
+    ///Translate throuth pagetable
     pub fn translate(&self, vpn: VirtPageNum) -> Option<PageTableEntry> {
         self.page_table.translate(vpn)
     }
+    ///Remove all `MapArea`
     pub fn recycle_data_pages(&mut self) {
         //*self = Self::new_bare();
         self.areas.clear();
     }
 }
-
+/// map area structure, controls a contiguous piece of virtual memory
 pub struct MapArea {
     vpn_range: VPNRange,
     data_frames: BTreeMap<VirtPageNum, FrameTracker>,
@@ -353,21 +362,28 @@ impl MapArea {
 }
 
 #[derive(Copy, Clone, PartialEq, Debug)]
+/// map type for memory set: identical or framed
 pub enum MapType {
     Identical,
     Framed,
 }
 
 bitflags! {
+    /// map permission corresponding to that in pte: `R W X U`
     pub struct MapPermission: u8 {
+        ///Readable
         const R = 1 << 1;
+        ///Writable
         const W = 1 << 2;
+        ///Excutable
         const X = 1 << 3;
+        ///Accessible in U mode
         const U = 1 << 4;
     }
 }
 
 #[allow(unused)]
+///Check PageTable running correctly
 pub fn remap_test() {
     let mut kernel_space = KERNEL_SPACE.exclusive_access();
     let mid_text: VirtAddr = ((stext as usize + etext as usize) / 2).into();
diff --git a/os/src/mm/mod.rs b/os/src/mm/mod.rs
index 34220c4a..5ebf92da 100644
--- a/os/src/mm/mod.rs
+++ b/os/src/mm/mod.rs
@@ -1,3 +1,10 @@
+//! Memory management implementation
+//! 
+//! SV39 page-based virtual-memory architecture for RV64 systems, and
+//! everything about memory management, like frame allocator, page table,
+//! map area and memory set, is implemented here.
+//! 
+//! Every task or process has a memory_set to control its virtual memory.
 mod address;
 mod frame_allocator;
 mod heap_allocator;
@@ -14,7 +21,7 @@ pub use page_table::{
     translated_byte_buffer, translated_ref, translated_refmut, translated_str, PageTable,
     PageTableEntry, UserBuffer, UserBufferIterator,
 };
-
+/// initiate heap allocator, frame allocator and kernel space
 pub fn init() {
     heap_allocator::init_heap();
     frame_allocator::init_frame_allocator();
diff --git a/os/src/mm/page_table.rs b/os/src/mm/page_table.rs
index 04d1894a..a76e938a 100644
--- a/os/src/mm/page_table.rs
+++ b/os/src/mm/page_table.rs
@@ -1,3 +1,4 @@
+//! Implementation of [`PageTableEntry`] and [`PageTable`].
 use super::{frame_alloc, FrameTracker, PhysAddr, PhysPageNum, StepByOne, VirtAddr, VirtPageNum};
 use alloc::string::String;
 use alloc::vec;
@@ -19,39 +20,49 @@ bitflags! {
 
 #[derive(Copy, Clone)]
 #[repr(C)]
+/// page table entry structure
 pub struct PageTableEntry {
+    ///PTE
     pub bits: usize,
 }
 
 impl PageTableEntry {
+    ///Create a PTE from ppn
     pub fn new(ppn: PhysPageNum, flags: PTEFlags) -> Self {
         PageTableEntry {
             bits: ppn.0 << 10 | flags.bits as usize,
         }
     }
+    ///Return an empty PTE
     pub fn empty() -> Self {
         PageTableEntry { bits: 0 }
     }
+    ///Return 44bit ppn 
     pub fn ppn(&self) -> PhysPageNum {
         (self.bits >> 10 & ((1usize << 44) - 1)).into()
     }
+    ///Return 10bit flag
     pub fn flags(&self) -> PTEFlags {
         PTEFlags::from_bits(self.bits as u8).unwrap()
     }
+    ///Check PTE valid
     pub fn is_valid(&self) -> bool {
         (self.flags() & PTEFlags::V) != PTEFlags::empty()
     }
+    ///Check PTE readable
     pub fn readable(&self) -> bool {
         (self.flags() & PTEFlags::R) != PTEFlags::empty()
     }
+    ///Check PTE writable
     pub fn writable(&self) -> bool {
         (self.flags() & PTEFlags::W) != PTEFlags::empty()
     }
+    ///Check PTE executable
     pub fn executable(&self) -> bool {
         (self.flags() & PTEFlags::X) != PTEFlags::empty()
     }
 }
-
+///Record root ppn and has the same lifetime as 1 and 2 level `PageTableEntry`
 pub struct PageTable {
     root_ppn: PhysPageNum,
     frames: Vec<FrameTracker>,
@@ -59,6 +70,7 @@ pub struct PageTable {
 
 /// Assume that it won't oom when creating/mapping.
 impl PageTable {
+    /// Create an empty `PageTable`
     pub fn new() -> Self {
         let frame = frame_alloc().unwrap();
         PageTable {
@@ -73,6 +85,7 @@ impl PageTable {
             frames: Vec::new(),
         }
     }
+    /// Find phsical address by virtual address, create a frame if not exist
     fn find_pte_create(&mut self, vpn: VirtPageNum) -> Option<&mut PageTableEntry> {
         let idxs = vpn.indexes();
         let mut ppn = self.root_ppn;
@@ -92,6 +105,7 @@ impl PageTable {
         }
         result
     }
+    /// Find phsical address by virtual address
     fn find_pte(&self, vpn: VirtPageNum) -> Option<&mut PageTableEntry> {
         let idxs = vpn.indexes();
         let mut ppn = self.root_ppn;
@@ -110,20 +124,24 @@ impl PageTable {
         result
     }
     #[allow(unused)]
+    /// Create a mapping form `vpn` to `ppn`
     pub fn map(&mut self, vpn: VirtPageNum, ppn: PhysPageNum, flags: PTEFlags) {
         let pte = self.find_pte_create(vpn).unwrap();
         assert!(!pte.is_valid(), "vpn {:?} is mapped before mapping", vpn);
         *pte = PageTableEntry::new(ppn, flags | PTEFlags::V);
     }
     #[allow(unused)]
+    /// Delete a mapping form `vpn`
     pub fn unmap(&mut self, vpn: VirtPageNum) {
         let pte = self.find_pte(vpn).unwrap();
         assert!(pte.is_valid(), "vpn {:?} is invalid before unmapping", vpn);
         *pte = PageTableEntry::empty();
     }
+    /// Translate `VirtPageNum` to `PageTableEntry`
     pub fn translate(&self, vpn: VirtPageNum) -> Option<PageTableEntry> {
         self.find_pte(vpn).map(|pte| *pte)
     }
+    /// Translate `VirtAddr` to `PhysAddr`
     pub fn translate_va(&self, va: VirtAddr) -> Option<PhysAddr> {
         self.find_pte(va.clone().floor()).map(|pte| {
             let aligned_pa: PhysAddr = pte.ppn().into();
@@ -132,12 +150,13 @@ impl PageTable {
             (aligned_pa_usize + offset).into()
         })
     }
+    /// Get root ppn 
     pub fn token(&self) -> usize {
         8usize << 60 | self.root_ppn.0
     }
 }
-
-pub fn translated_byte_buffer(token: usize, ptr: *const u8, len: usize) -> Vec<&'static mut [u8]> {
+    /// Translate a pointer to a mutable u8 Vec through page table
+    pub fn translated_byte_buffer(token: usize, ptr: *const u8, len: usize) -> Vec<&'static mut [u8]> {
     let page_table = PageTable::from_token(token);
     let mut start = ptr as usize;
     let end = start + len;
@@ -159,7 +178,7 @@ pub fn translated_byte_buffer(token: usize, ptr: *const u8, len: usize) -> Vec<&
     v
 }
 
-/// Load a string from other address spaces into kernel space without an end `\0`.
+/// Translate a pointer to a mutable u8 Vec end with `\0` through page table to a `String`
 pub fn translated_str(token: usize, ptr: *const u8) -> String {
     let page_table = PageTable::from_token(token);
     let mut string = String::new();
@@ -179,6 +198,7 @@ pub fn translated_str(token: usize, ptr: *const u8) -> String {
 }
 
 #[allow(unused)]
+///Translate a generic through page table and return a reference
 pub fn translated_ref<T>(token: usize, ptr: *const T) -> &'static T {
     let page_table = PageTable::from_token(token);
     page_table
@@ -186,7 +206,7 @@ pub fn translated_ref<T>(token: usize, ptr: *const T) -> &'static T {
         .unwrap()
         .get_ref()
 }
-
+///Translate a generic through page table and return a mutable reference
 pub fn translated_refmut<T>(token: usize, ptr: *mut T) -> &'static mut T {
     let page_table = PageTable::from_token(token);
     let va = ptr as usize;
@@ -195,15 +215,18 @@ pub fn translated_refmut<T>(token: usize, ptr: *mut T) -> &'static mut T {
         .unwrap()
         .get_mut()
 }
-
+///Array of u8 slice that user communicate with os
 pub struct UserBuffer {
+    ///U8 vec
     pub buffers: Vec<&'static mut [u8]>,
 }
 
 impl UserBuffer {
+    ///Create a `UserBuffer` by parameter
     pub fn new(buffers: Vec<&'static mut [u8]>) -> Self {
         Self { buffers }
     }
+    ///Length of `UserBuffer`
     pub fn len(&self) -> usize {
         let mut total: usize = 0;
         for b in self.buffers.iter() {
@@ -224,7 +247,7 @@ impl IntoIterator for UserBuffer {
         }
     }
 }
-
+/// Iterator of `UserBuffer`
 pub struct UserBufferIterator {
     buffers: Vec<&'static mut [u8]>,
     current_buffer: usize,
diff --git a/os/src/sbi.rs b/os/src/sbi.rs
index 2e2804b2..06f31a75 100644
--- a/os/src/sbi.rs
+++ b/os/src/sbi.rs
@@ -1,3 +1,4 @@
+//! SBI call wrappers
 #![allow(unused)]
 
 use core::arch::asm;
@@ -11,7 +12,7 @@ const SBI_REMOTE_FENCE_I: usize = 5;
 const SBI_REMOTE_SFENCE_VMA: usize = 6;
 const SBI_REMOTE_SFENCE_VMA_ASID: usize = 7;
 const SBI_SHUTDOWN: usize = 8;
-
+/// general sbi call
 #[inline(always)]
 fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
@@ -26,19 +27,19 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     }
     ret
 }
-
+/// use sbi call to set timer
 pub fn set_timer(timer: usize) {
     sbi_call(SBI_SET_TIMER, timer, 0, 0);
 }
-
+/// use sbi call to putchar in console (qemu uart handler)
 pub fn console_putchar(c: usize) {
     sbi_call(SBI_CONSOLE_PUTCHAR, c, 0, 0);
 }
-
+/// use sbi call to getchar from console (qemu uart handler)
 pub fn console_getchar() -> usize {
     sbi_call(SBI_CONSOLE_GETCHAR, 0, 0, 0)
 }
-
+/// use sbi call to shutdown the kernel
 pub fn shutdown() -> ! {
     sbi_call(SBI_SHUTDOWN, 0, 0, 0);
     panic!("It should shutdown!");
diff --git a/os/src/sync/mod.rs b/os/src/sync/mod.rs
index d1ce5bcf..aa04db35 100644
--- a/os/src/sync/mod.rs
+++ b/os/src/sync/mod.rs
@@ -1,3 +1,4 @@
+//! Synchronization and interior mutability primitives
 mod up;
 
 pub use up::UPSafeCell;
diff --git a/os/src/sync/up.rs b/os/src/sync/up.rs
index c7b2c9ee..955b9dc0 100644
--- a/os/src/sync/up.rs
+++ b/os/src/sync/up.rs
@@ -1,3 +1,4 @@
+//! Uniprocessor interior mutability primitives
 use core::cell::{RefCell, RefMut};
 
 /// Wrap a static data structure inside it so that we are
@@ -22,7 +23,7 @@ impl<T> UPSafeCell<T> {
             inner: RefCell::new(value),
         }
     }
-    /// Panic if the data has been borrowed.
+    /// Exclusive access inner data in UPSafeCell. Panic if the data has been borrowed.
     pub fn exclusive_access(&self) -> RefMut<'_, T> {
         self.inner.borrow_mut()
     }
diff --git a/os/src/syscall/fs.rs b/os/src/syscall/fs.rs
index dbaa4eaf..aecc7903 100644
--- a/os/src/syscall/fs.rs
+++ b/os/src/syscall/fs.rs
@@ -1,3 +1,4 @@
+//! File and filesystem-related syscalls
 use crate::fs::{open_file, OpenFlags};
 use crate::mm::{translated_byte_buffer, translated_str, UserBuffer};
 use crate::task::{current_task, current_user_token};
diff --git a/os/src/syscall/mod.rs b/os/src/syscall/mod.rs
index 8c5f6e3f..8bcb3269 100644
--- a/os/src/syscall/mod.rs
+++ b/os/src/syscall/mod.rs
@@ -1,3 +1,14 @@
+//! Implementation of syscalls
+//!
+//! The single entry point to all system calls, [`syscall()`], is called
+//! whenever userspace wishes to perform a system call using the `ecall`
+//! instruction. In this case, the processor raises an 'Environment call from
+//! U-mode' exception, which is handled as one of the cases in
+//! [`crate::trap::trap_handler`].
+//!
+//! For clarity, each single syscall is implemented as its own function, named
+//! `sys_` then the name of the syscall. You can find functions like this in
+//! submodules, and you should also implement syscalls this way.
 const SYSCALL_OPEN: usize = 56;
 const SYSCALL_CLOSE: usize = 57;
 const SYSCALL_READ: usize = 63;
@@ -15,7 +26,7 @@ mod process;
 
 use fs::*;
 use process::*;
-
+/// handle syscall exception with `syscall_id` and other arguments
 pub fn syscall(syscall_id: usize, args: [usize; 3]) -> isize {
     match syscall_id {
         SYSCALL_OPEN => sys_open(args[0] as *const u8, args[1] as u32),
diff --git a/os/src/task/context.rs b/os/src/task/context.rs
index e4f59d8a..520bce17 100644
--- a/os/src/task/context.rs
+++ b/os/src/task/context.rs
@@ -1,13 +1,19 @@
+//! Implementation of [`TaskContext`]
 use crate::trap::trap_return;
 
 #[repr(C)]
+/// task context structure containing some registers
 pub struct TaskContext {
+    /// return address ( e.g. __restore ) of __switch ASM function
     ra: usize,
+    /// kernel stack pointer of app
     sp: usize,
+    /// s0-11 register, callee saved
     s: [usize; 12],
 }
 
 impl TaskContext {
+    /// init task context
     pub fn zero_init() -> Self {
         Self {
             ra: 0,
@@ -15,6 +21,7 @@ impl TaskContext {
             s: [0; 12],
         }
     }
+    /// set Task Context{__restore ASM funciton: trap_return, sp: kstack_ptr, s: s_0..12}
     pub fn goto_trap_return(kstack_ptr: usize) -> Self {
         Self {
             ra: trap_return as usize,
diff --git a/os/src/task/manager.rs b/os/src/task/manager.rs
index 542a0b87..315cd224 100644
--- a/os/src/task/manager.rs
+++ b/os/src/task/manager.rs
@@ -1,23 +1,27 @@
+//!Implementation of [`TaskManager`]
 use super::TaskControlBlock;
 use crate::sync::UPSafeCell;
 use alloc::collections::VecDeque;
 use alloc::sync::Arc;
 use lazy_static::*;
-
+///A array of `TaskControlBlock` that is thread-safe
 pub struct TaskManager {
     ready_queue: VecDeque<Arc<TaskControlBlock>>,
 }
 
 /// A simple FIFO scheduler.
 impl TaskManager {
+    ///Creat an empty TaskManager
     pub fn new() -> Self {
         Self {
             ready_queue: VecDeque::new(),
         }
     }
+    ///Add a task to `TaskManager`
     pub fn add(&mut self, task: Arc<TaskControlBlock>) {
         self.ready_queue.push_back(task);
     }
+    ///Remove the first task and return it,or `None` if `TaskManager` is empty
     pub fn fetch(&mut self) -> Option<Arc<TaskControlBlock>> {
         self.ready_queue.pop_front()
     }
@@ -27,11 +31,11 @@ lazy_static! {
     pub static ref TASK_MANAGER: UPSafeCell<TaskManager> =
         unsafe { UPSafeCell::new(TaskManager::new()) };
 }
-
+///Interface offered to add task
 pub fn add_task(task: Arc<TaskControlBlock>) {
     TASK_MANAGER.exclusive_access().add(task);
 }
-
+///Interface offered to pop the first task
 pub fn fetch_task() -> Option<Arc<TaskControlBlock>> {
     TASK_MANAGER.exclusive_access().fetch()
 }
diff --git a/os/src/task/mod.rs b/os/src/task/mod.rs
index 78853ee2..1c5dc90a 100644
--- a/os/src/task/mod.rs
+++ b/os/src/task/mod.rs
@@ -1,25 +1,42 @@
+//! Task management implementation
+//!
+//! Everything about task management, like starting and switching tasks is
+//! implemented here.
+//!
+//! A single global instance of [`TaskManager`] called `TASK_MANAGER` controls
+//! all the tasks in the whole operating system.
+//! 
+//! A single global instance of [`Processor`] called `PROCESSOR` monitors running 
+//! task(s) for each core. 
+//! 
+//! A single global instance of [`PidAllocator`] called `PID_ALLOCATOR` allocates 
+//! pid for user apps.
+//! 
+//! Be careful when you see `__switch` ASM function in `switch.S`. Control flow around this function
+//! might not be what you expect.
 mod context;
 mod manager;
 mod pid;
 mod processor;
 mod switch;
 #[allow(clippy::module_inception)]
+#[allow(rustdoc::private_intra_doc_links)]
 mod task;
 
 use crate::fs::{open_file, OpenFlags};
 use alloc::sync::Arc;
 pub use context::TaskContext;
 use lazy_static::*;
-use manager::fetch_task;
+pub use manager::{fetch_task,TaskManager};
 use switch::__switch;
 use task::{TaskControlBlock, TaskStatus};
 
 pub use manager::add_task;
-pub use pid::{pid_alloc, KernelStack, PidHandle};
+pub use pid::{pid_alloc, KernelStack, PidHandle,PidAllocator};
 pub use processor::{
-    current_task, current_trap_cx, current_user_token, run_tasks, schedule, take_current_task,
+    current_task, current_trap_cx, current_user_token, run_tasks, schedule, take_current_task,Processor
 };
-
+/// Suspend the current 'Running' task and run the next task in task list.
 pub fn suspend_current_and_run_next() {
     // There must be an application running.
     let task = take_current_task().unwrap();
@@ -37,7 +54,7 @@ pub fn suspend_current_and_run_next() {
     // jump to scheduling cycle
     schedule(task_cx_ptr);
 }
-
+/// Exit the current 'Running' task and run the next task in task list.
 pub fn exit_current_and_run_next(exit_code: i32) {
     // take from Processor
     let task = take_current_task().unwrap();
@@ -72,13 +89,14 @@ pub fn exit_current_and_run_next(exit_code: i32) {
 }
 
 lazy_static! {
+    ///Globle process that init user shell 
     pub static ref INITPROC: Arc<TaskControlBlock> = Arc::new({
         let inode = open_file("initproc", OpenFlags::RDONLY).unwrap();
         let v = inode.read_all();
         TaskControlBlock::new(v.as_slice())
     });
 }
-
+///Add init process to the manager
 pub fn add_initproc() {
     add_task(INITPROC.clone());
 }
diff --git a/os/src/task/pid.rs b/os/src/task/pid.rs
index 9e33efdc..7c8799e6 100644
--- a/os/src/task/pid.rs
+++ b/os/src/task/pid.rs
@@ -1,21 +1,24 @@
+//!Implementation of [`PidAllocator`]
 use crate::config::{KERNEL_STACK_SIZE, PAGE_SIZE, TRAMPOLINE};
 use crate::mm::{MapPermission, VirtAddr, KERNEL_SPACE};
 use crate::sync::UPSafeCell;
 use alloc::vec::Vec;
 use lazy_static::*;
-
-struct PidAllocator {
+///Pid Allocator struct
+pub struct PidAllocator {
     current: usize,
     recycled: Vec<usize>,
 }
 
 impl PidAllocator {
+    ///Create an empty `PidAllocator`
     pub fn new() -> Self {
         PidAllocator {
             current: 0,
             recycled: Vec::new(),
         }
     }
+    ///Allocate a pid
     pub fn alloc(&mut self) -> PidHandle {
         if let Some(pid) = self.recycled.pop() {
             PidHandle(pid)
@@ -24,6 +27,7 @@ impl PidAllocator {
             PidHandle(self.current - 1)
         }
     }
+    ///Recycle a pid
     pub fn dealloc(&mut self, pid: usize) {
         assert!(pid < self.current);
         assert!(
@@ -36,10 +40,10 @@ impl PidAllocator {
 }
 
 lazy_static! {
-    static ref PID_ALLOCATOR: UPSafeCell<PidAllocator> =
+    pub static ref PID_ALLOCATOR: UPSafeCell<PidAllocator> =
         unsafe { UPSafeCell::new(PidAllocator::new()) };
 }
-
+///Bind pid lifetime to `PidHandle`
 pub struct PidHandle(pub usize);
 
 impl Drop for PidHandle {
@@ -48,7 +52,7 @@ impl Drop for PidHandle {
         PID_ALLOCATOR.exclusive_access().dealloc(self.0);
     }
 }
-
+///Allocate a pid from PID_ALLOCATOR
 pub fn pid_alloc() -> PidHandle {
     PID_ALLOCATOR.exclusive_access().alloc()
 }
@@ -59,12 +63,13 @@ pub fn kernel_stack_position(app_id: usize) -> (usize, usize) {
     let bottom = top - KERNEL_STACK_SIZE;
     (bottom, top)
 }
-
+///Kernelstack for app 
 pub struct KernelStack {
     pid: usize,
 }
 
 impl KernelStack {
+    ///Create a kernelstack from pid
     pub fn new(pid_handle: &PidHandle) -> Self {
         let pid = pid_handle.0;
         let (kernel_stack_bottom, kernel_stack_top) = kernel_stack_position(pid);
@@ -76,6 +81,7 @@ impl KernelStack {
         KernelStack { pid: pid_handle.0 }
     }
     #[allow(unused)]
+    ///Push a value on top of kernelstack
     pub fn push_on_top<T>(&self, value: T) -> *mut T
     where
         T: Sized,
@@ -87,6 +93,7 @@ impl KernelStack {
         }
         ptr_mut
     }
+    ///Get the value on the top of kernelstack
     pub fn get_top(&self) -> usize {
         let (_, kernel_stack_top) = kernel_stack_position(self.pid);
         kernel_stack_top
diff --git a/os/src/task/processor.rs b/os/src/task/processor.rs
index e1fac0aa..1d9c0f2d 100644
--- a/os/src/task/processor.rs
+++ b/os/src/task/processor.rs
@@ -1,3 +1,4 @@
+//!Implementation of [`Processor`] and Intersection of control flow
 use super::__switch;
 use super::{fetch_task, TaskStatus};
 use super::{TaskContext, TaskControlBlock};
@@ -5,25 +6,31 @@ use crate::sync::UPSafeCell;
 use crate::trap::TrapContext;
 use alloc::sync::Arc;
 use lazy_static::*;
-
+///Processor management structure
 pub struct Processor {
+    ///The task currently executing on the current processor
     current: Option<Arc<TaskControlBlock>>,
+    ///The basic control flow of each core, helping to select and switch process
     idle_task_cx: TaskContext,
 }
 
 impl Processor {
+    ///Create an empty Processor
     pub fn new() -> Self {
         Self {
             current: None,
             idle_task_cx: TaskContext::zero_init(),
         }
     }
+    ///Get mutable reference to `idle_task_cx`
     fn get_idle_task_cx_ptr(&mut self) -> *mut TaskContext {
         &mut self.idle_task_cx as *mut _
     }
+    ///Get current task in moving semanteme
     pub fn take_current(&mut self) -> Option<Arc<TaskControlBlock>> {
         self.current.take()
     }
+    ///Get current task in cloning semanteme
     pub fn current(&self) -> Option<Arc<TaskControlBlock>> {
         self.current.as_ref().map(Arc::clone)
     }
@@ -32,7 +39,8 @@ impl Processor {
 lazy_static! {
     pub static ref PROCESSOR: UPSafeCell<Processor> = unsafe { UPSafeCell::new(Processor::new()) };
 }
-
+///The main part of process execution and scheduling
+///Loop `fetch_task` to get the process that needs to run, and switch the process through `__switch`
 pub fn run_tasks() {
     loop {
         let mut processor = PROCESSOR.exclusive_access();
@@ -53,28 +61,28 @@ pub fn run_tasks() {
         }
     }
 }
-
+///Take the current task,leaving a None in its place
 pub fn take_current_task() -> Option<Arc<TaskControlBlock>> {
     PROCESSOR.exclusive_access().take_current()
 }
-
+///Get running task
 pub fn current_task() -> Option<Arc<TaskControlBlock>> {
     PROCESSOR.exclusive_access().current()
 }
-
+///Get token of the address space of current task
 pub fn current_user_token() -> usize {
     let task = current_task().unwrap();
     let token = task.inner_exclusive_access().get_user_token();
     token
 }
-
+///Get the mutable reference to trap context of current task
 pub fn current_trap_cx() -> &'static mut TrapContext {
     current_task()
         .unwrap()
         .inner_exclusive_access()
         .get_trap_cx()
 }
-
+///Return to idle control flow for new scheduling
 pub fn schedule(switched_task_cx_ptr: *mut TaskContext) {
     let mut processor = PROCESSOR.exclusive_access();
     let idle_task_cx_ptr = processor.get_idle_task_cx_ptr();
diff --git a/os/src/task/switch.rs b/os/src/task/switch.rs
index 59f8b1a0..7d194f52 100644
--- a/os/src/task/switch.rs
+++ b/os/src/task/switch.rs
@@ -1,3 +1,4 @@
+//!Wrap `switch.S` as a function
 use super::TaskContext;
 use core::arch::global_asm;
 
diff --git a/os/src/task/task.rs b/os/src/task/task.rs
index b5b917dd..101415b3 100644
--- a/os/src/task/task.rs
+++ b/os/src/task/task.rs
@@ -1,3 +1,4 @@
+//!Implementation of [`TaskControlBlock`] 
 use super::TaskContext;
 use super::{pid_alloc, KernelStack, PidHandle};
 use crate::config::TRAP_CONTEXT;
diff --git a/os/src/timer.rs b/os/src/timer.rs
index 048aa3b7..a491faaa 100644
--- a/os/src/timer.rs
+++ b/os/src/timer.rs
@@ -1,18 +1,21 @@
+
+//! RISC-V timer-related functionality
+
 use crate::config::CLOCK_FREQ;
 use crate::sbi::set_timer;
 use riscv::register::time;
 
 const TICKS_PER_SEC: usize = 100;
 const MSEC_PER_SEC: usize = 1000;
-
+///get current time
 pub fn get_time() -> usize {
     time::read()
 }
-
+/// get current time in microseconds
 pub fn get_time_ms() -> usize {
     time::read() / (CLOCK_FREQ / MSEC_PER_SEC)
 }
-
+/// set the next timer interrupt
 pub fn set_next_trigger() {
     set_timer(get_time() + CLOCK_FREQ / TICKS_PER_SEC);
 }
diff --git a/os/src/trap/context.rs b/os/src/trap/context.rs
index 011b7fb7..0cae4929 100644
--- a/os/src/trap/context.rs
+++ b/os/src/trap/context.rs
@@ -1,20 +1,30 @@
+//! Implementation of [`TrapContext`]
 use riscv::register::sstatus::{self, Sstatus, SPP};
 
 #[repr(C)]
 #[derive(Debug)]
+///trap context structure containing sstatus, sepc and registers
 pub struct TrapContext {
+    /// general regs[0..31]
     pub x: [usize; 32],
+    /// CSR sstatus      
     pub sstatus: Sstatus,
+    /// CSR sepc
     pub sepc: usize,
+    /// Addr of Page Table
     pub kernel_satp: usize,
+    /// kernel stack
     pub kernel_sp: usize,
+    /// Addr of trap_handler function
     pub trap_handler: usize,
 }
 
 impl TrapContext {
+    ///set stack pointer to x_2 reg (sp)
     pub fn set_sp(&mut self, sp: usize) {
         self.x[2] = sp;
     }
+    ///init app context
     pub fn app_init_context(
         entry: usize,
         sp: usize,
diff --git a/os/src/trap/mod.rs b/os/src/trap/mod.rs
index 4c9a1128..f0684401 100644
--- a/os/src/trap/mod.rs
+++ b/os/src/trap/mod.rs
@@ -1,3 +1,16 @@
+//! Trap handling functionality
+//!
+//! For rCore, we have a single trap entry point, namely `__alltraps`. At
+//! initialization in [`init()`], we set the `stvec` CSR to point to it.
+//!
+//! All traps go through `__alltraps`, which is defined in `trap.S`. The
+//! assembly language code does just enough work restore the kernel space
+//! context, ensuring that Rust code safely runs, and transfers control to
+//! [`trap_handler()`].
+//!
+//! It then calls different functionality based on what exactly the exception
+//! was. For example, timer interrupts trigger task preemption, and syscalls go
+//! to [`syscall()`].
 mod context;
 
 use crate::config::{TRAMPOLINE, TRAP_CONTEXT};
@@ -14,7 +27,7 @@ use riscv::register::{
 };
 
 global_asm!(include_str!("trap.S"));
-
+/// initialize CSR `stvec` as the entry of `__alltraps`
 pub fn init() {
     set_kernel_trap_entry();
 }
@@ -30,7 +43,7 @@ fn set_user_trap_entry() {
         stvec::write(TRAMPOLINE as usize, TrapMode::Direct);
     }
 }
-
+/// enable timer interrupt in sie CSR
 pub fn enable_timer_interrupt() {
     unsafe {
         sie::set_stimer();
@@ -38,6 +51,7 @@ pub fn enable_timer_interrupt() {
 }
 
 #[no_mangle]
+/// handle an interrupt, exception, or system call from user space
 pub fn trap_handler() -> ! {
     set_kernel_trap_entry();
     let scause = scause::read();
@@ -90,6 +104,9 @@ pub fn trap_handler() -> ! {
 }
 
 #[no_mangle]
+/// set the new addr of __restore asm function in TRAMPOLINE page,
+/// set the reg a0 = trap_cx_ptr, reg a1 = phy addr of usr page table,
+/// finally, jump to new addr of __restore asm function 
 pub fn trap_return() -> ! {
     set_user_trap_entry();
     let trap_cx_ptr = TRAP_CONTEXT;
@@ -112,6 +129,8 @@ pub fn trap_return() -> ! {
 }
 
 #[no_mangle]
+/// Unimplement: traps/interrupts/exceptions from kernel mode
+/// Todo: Chapter 9: I/O device 
 pub fn trap_from_kernel() -> ! {
     use riscv::register::sepc;
     println!("stval = {:#x}, sepc = {:#x}", stval::read(), sepc::read());