diff --git a/.travis.yml b/.travis.yml
index 0e9d60b..d7f343e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,7 @@ sudo: required
 
 language: rust
 
-rust: nightly-2018-08-03
+rust: nightly-2018-09-18
 
 cache:
   cargo: true
@@ -10,7 +10,6 @@ cache:
 addons:
   apt:
     packages:
-      - nasm
       - qemu
 
 env:
@@ -28,9 +27,8 @@ install:
 
 before_script:
   - rustup component add rust-src
-  - (test -x $HOME/.cargo/bin/cargo-install-update || cargo install cargo-update)
   - (test -x $HOME/.cargo/bin/cargo-xbuild || cargo install cargo-xbuild)
-  - cargo install-update -a
+  - (test -x $HOME/.cargo/bin/bootimage || cargo install bootimage)
 
 script:
   - cd kernel && make build arch=$ARCH
diff --git a/README.md b/README.md
index 9017fc5..3f45e3b 100644
--- a/README.md
+++ b/README.md
@@ -22,22 +22,22 @@ In fact, it's more complicated than we expected to write an OS starting from scr
 
 ### Environment
 
-* Rust toolchain at nightly-2018-09-03
-*  `cargo-xbuild`
-* `QEMU` >= 2.12.0
-* riscv32
-  * RISCV64 GNU toolchain
-* x86_64
-  * `nasm`
-  * `grub-mkrescue`
-  * `xorriso`
+* [Rust](https://www.rust-lang.org) toolchain at nightly-2018-09-18
+* Cargo tools: [cargo-xbuild](https://github.com/rust-osdev/cargo-xbuild), [bootimage](https://github.com/rust-osdev/bootimage)
+* QEMU >= 2.12.0
+* [RISCV64 GNU toolchain](https://www.sifive.com/products/tools/) (for riscv32)
 
 ### How to run
 
+```bash
+rustup component add rust-src
+cargo install cargo-xbuild bootimage
+```
+
 ```bash
 git clone https://github.com/wangrunji0408/RustOS.git --recursive
 cd RustOS/kernel
-rustup override set nightly-2018-09-03
+rustup override set nightly-2018-09-18
 make run arch=riscv32|x86_64
 # For FPGA: 
 # make run arch=riscv32 board=1
diff --git a/crate/riscv b/crate/riscv
index 50d2008..f358204 160000
--- a/crate/riscv
+++ b/crate/riscv
@@ -1 +1 @@
-Subproject commit 50d2008d7579e24fc4f29889b73831acdd9aa830
+Subproject commit f358204af01f2374ab6ed6ea059f724cd5f2fe6f
diff --git a/kernel/Makefile b/kernel/Makefile
index ff631a7..0053184 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -38,7 +38,6 @@ endif
 ifeq ($(arch), riscv32)
 qemu_opts := -machine virt -kernel $(bin) -nographic
 endif
-features := use_apic
 
 ifdef board
 features := $(features) no_bbl
@@ -78,7 +77,7 @@ objdump := $(prefix)objdump
 cc := $(prefix)gcc
 as := $(prefix)as
 
-.PHONY: all clean run build asm doc justrun
+.PHONY: all clean run build asm doc justrun kernel
 
 all: $(kernel)
 
@@ -97,7 +96,7 @@ debug: $(bin)
 	@qemu-system-$(arch) $(qemu_opts) -s -S &
 
 ifeq ($(arch), x86_64)
-build: $(kernel)
+build: kernel
 else
 build: $(bin)
 endif
@@ -108,7 +107,7 @@ asm:
 elf-h:
 	@$(objdump) -h $(kernel)
 
-$(bin): $(kernel)
+$(bin): kernel
 ifdef board
 	@cp $(kernel) $@
 else
@@ -125,7 +124,7 @@ else
 	 cp bbl ../../kernel/$@
 endif
 
-$(kernel):
+kernel:
 ifeq ($(arch), x86_64)
 	@bootimage build $(build_args)
 else