diff --git a/crate/bcm2837/Cargo.toml b/crate/bcm2837/Cargo.toml
index 3fb3e2e..456ee0e 100644
--- a/crate/bcm2837/Cargo.toml
+++ b/crate/bcm2837/Cargo.toml
@@ -2,10 +2,11 @@
 name = "bcm2837"
 version = "0.1.0"
 authors = ["equation314 <equation618@gmail.com>"]
+edition = "2018"
 
 [features]
-use_generic_timer = []
+use_generic_timer = ["aarch64"]
 
 [dependencies]
 volatile = "0.2.4"
-cortex-a = "2.2.2"
+aarch64= { git = "https://github.com/equation314/aarch64", optional = true }
diff --git a/crate/bcm2837/src/gpio.rs b/crate/bcm2837/src/gpio.rs
index 1fb7fec..ef258d6 100644
--- a/crate/bcm2837/src/gpio.rs
+++ b/crate/bcm2837/src/gpio.rs
@@ -1,5 +1,5 @@
-use IO_BASE;
-use timer::delay;
+use crate::IO_BASE;
+use crate::timer::delay;
 use core::marker::PhantomData;
 use volatile::{ReadOnly, Volatile, WriteOnly};
 
diff --git a/crate/bcm2837/src/interrupt.rs b/crate/bcm2837/src/interrupt.rs
index 9d6befe..03657c9 100644
--- a/crate/bcm2837/src/interrupt.rs
+++ b/crate/bcm2837/src/interrupt.rs
@@ -1,4 +1,4 @@
-use IO_BASE;
+use crate::IO_BASE;
 use volatile::{ReadOnly, Volatile};
 
 const INT_BASE: usize = IO_BASE + 0xB000 + 0x200;
diff --git a/crate/bcm2837/src/mini_uart.rs b/crate/bcm2837/src/mini_uart.rs
index d21c249..c1d0101 100644
--- a/crate/bcm2837/src/mini_uart.rs
+++ b/crate/bcm2837/src/mini_uart.rs
@@ -1,5 +1,5 @@
-use IO_BASE;
-use gpio::{Function, Gpio};
+use crate::IO_BASE;
+use crate::gpio::{Function, Gpio};
 use volatile::{ReadOnly, Volatile};
 
 /// The base address for the `MU` registers.
diff --git a/crate/bcm2837/src/timer/generic_timer.rs b/crate/bcm2837/src/timer/generic_timer.rs
index 14aabe6..8333cb9 100644
--- a/crate/bcm2837/src/timer/generic_timer.rs
+++ b/crate/bcm2837/src/timer/generic_timer.rs
@@ -1,6 +1,6 @@
-extern crate cortex_a;
+extern crate aarch64;
 
-use self::cortex_a::regs::*;
+use aarch64::regs::*;
 use volatile::*;
 
 /// The base address for the ARM generic timer, IRQs, mailboxes
diff --git a/crate/bcm2837/src/timer/system_timer.rs b/crate/bcm2837/src/timer/system_timer.rs
index cad2af4..4d5dc12 100644
--- a/crate/bcm2837/src/timer/system_timer.rs
+++ b/crate/bcm2837/src/timer/system_timer.rs
@@ -1,6 +1,6 @@
-use ::IO_BASE;
+use crate::IO_BASE;
+use crate::interrupt::{Controller, Interrupt};
 use volatile::{ReadOnly, Volatile};
-use interrupt::{Controller, Interrupt};
 
 /// The base address for the ARM system timer registers.
 const TIMER_REG_BASE: usize = IO_BASE + 0x3000;
diff --git a/kernel/Cargo.lock b/kernel/Cargo.lock
index f760ced..064af4a 100644
--- a/kernel/Cargo.lock
+++ b/kernel/Cargo.lock
@@ -48,7 +48,7 @@ version = "0.1.0"
 name = "bcm2837"
 version = "0.1.0"
 dependencies = [
- "cortex-a 2.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "aarch64 2.2.2 (git+https://github.com/equation314/aarch64)",
  "volatile 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -96,14 +96,6 @@ name = "cfg-if"
 version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "cortex-a"
-version = "2.2.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "register 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "fixedvec"
 version = "0.2.3"
@@ -453,7 +445,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum bootloader 0.3.4 (git+https://github.com/wangrunji0408/bootloader)" = "<none>"
 "checksum cc 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)" = "f159dfd43363c4d08055a07703eb7a3406b0dac4d0584d96965a3262db3c9d16"
 "checksum cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "082bb9b28e00d3c9d39cc03e64ce4cea0f1bb9b3fde493f0cbc008472d22bdf4"
-"checksum cortex-a 2.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "2b187d0d728b4a99ba1d79f9671b976bcdd71a8a2c719585218fd2dc14a4d08c"
 "checksum fixedvec 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7c6c16d316ccdac21a4dd648e314e76facbbaf316e83ca137d0857a9c07419d0"
 "checksum fuchsia-zircon 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "2e9763c69ebaae630ba35f74888db465e49e259ba1bc0eda7d06f4a067615d82"
 "checksum fuchsia-zircon-sys 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
diff --git a/kernel/Cargo.toml b/kernel/Cargo.toml
index aa429ce..6718500 100644
--- a/kernel/Cargo.toml
+++ b/kernel/Cargo.toml
@@ -12,7 +12,8 @@ no_mmu = []
 # Kernel in M-mode (for riscv32)
 m_mode = ["no_mmu"]
 # (for aarch64 RaspberryPi3)
-board_raspi3 = []
+board_raspi3 = ["bcm2837"]
+raspi3_use_generic_timer = ["bcm2837/use_generic_timer"]
 
 [profile.dev]
 # MUST >= 1 : Enable RVO to avoid stack overflow
@@ -53,7 +54,7 @@ bbl = { path = "../crate/bbl" }
 [target.'cfg(target_arch = "aarch64")'.dependencies]
 aarch64 = { git = "https://github.com/equation314/aarch64" }
 atags = { path = "../crate/atags" }
-bcm2837 = { path = "../crate/bcm2837", features = ["use_generic_timer"] }
+bcm2837 = { path = "../crate/bcm2837", optional = true }
 
 [package.metadata.bootimage]
 default-target = "x86_64-blog_os.json"
diff --git a/kernel/Makefile b/kernel/Makefile
index 87668a4..7173184 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -78,6 +78,15 @@ features += no_bbl
 endif
 endif
 
+ifeq ($(board), raspi3)
+# qemu only has generic timer
+# TODO: configure system/generic timer automatically
+raspi3_timer ?= generic
+ifeq ($(raspi3_timer), generic)
+features += raspi3_use_generic_timer
+endif
+endif
+
 ifdef m_mode
 features += no_mmu m_mode
 bbl_m_mode := --enable-boot-machine
diff --git a/kernel/src/arch/aarch64/board/raspi3/irq.rs b/kernel/src/arch/aarch64/board/raspi3/irq.rs
index a982947..d8730dc 100644
--- a/kernel/src/arch/aarch64/board/raspi3/irq.rs
+++ b/kernel/src/arch/aarch64/board/raspi3/irq.rs
@@ -6,7 +6,7 @@ pub use bcm2837::interrupt::Interrupt;
 
 static IRQ_HANDLERS: &'static [Option<fn()>; 64] = &[None; 64];
 
-pub fn handle_irq(tf: &mut TrapFrame) {
+pub fn handle_irq(_tf: &mut TrapFrame) {
     let controller = bcm2837::timer::Timer::new();
     if controller.is_pending() {
         super::timer::set_next();
@@ -16,9 +16,6 @@ pub fn handle_irq(tf: &mut TrapFrame) {
     for int in Controller::new().pending_interrupts() {
         if let Some(handler) = IRQ_HANDLERS[int] {
             handler();
-        } else {
-            error!("Unregistered IRQ {}", int);
-            crate::trap::error(tf);
         }
     }
 }
diff --git a/kernel/src/arch/aarch64/interrupt/context.rs b/kernel/src/arch/aarch64/interrupt/context.rs
index 8b231e7..0d6502c 100644
--- a/kernel/src/arch/aarch64/interrupt/context.rs
+++ b/kernel/src/arch/aarch64/interrupt/context.rs
@@ -99,7 +99,7 @@ impl Context {
     /// Pop all callee-saved registers, then return to the target.
     #[naked]
     #[inline(never)]
-    unsafe extern fn __switch(self_stack: &mut usize, target_stack: &mut usize) {
+    unsafe extern fn __switch(_self_stack: &mut usize, _target_stack: &mut usize) {
         asm!(
         "
         mov x10, #-(12 * 8)
@@ -149,7 +149,7 @@ impl Context {
             tf: TrapFrame::new_kernel_thread(entry, arg, kstack_top),
         }.push_at(kstack_top, ttbr)
     }
-    pub unsafe fn new_user_thread(entry_addr: usize, ustack_top: usize, kstack_top: usize, is32: bool, ttbr: usize) -> Self {
+    pub unsafe fn new_user_thread(entry_addr: usize, ustack_top: usize, kstack_top: usize, _is32: bool, ttbr: usize) -> Self {
         InitStack {
             context: ContextData::new(),
             tf: TrapFrame::new_user_thread(entry_addr, ustack_top),
diff --git a/kernel/src/arch/aarch64/memory.rs b/kernel/src/arch/aarch64/memory.rs
index cf86c76..6a5996f 100644
--- a/kernel/src/arch/aarch64/memory.rs
+++ b/kernel/src/arch/aarch64/memory.rs
@@ -99,7 +99,7 @@ fn init_frame_allocator() {
 
 /// remap kernel page table after all initialization.
 fn remap_the_kernel() {
-    let mut ms = unsafe { MemorySet::new_bare() };
+    let mut ms = MemorySet::new_bare();
     ms.push(MemoryArea::new_identity(0, bootstacktop as usize, MemoryAttr::default(), "kstack"));
     ms.push(MemoryArea::new_identity(stext as usize, etext as usize, MemoryAttr::default().execute().readonly(), "text"));
     ms.push(MemoryArea::new_identity(sdata as usize, edata as usize, MemoryAttr::default(), "data"));
diff --git a/kernel/src/arch/aarch64/paging.rs b/kernel/src/arch/aarch64/paging.rs
index 14426d7..fa0e074 100644
--- a/kernel/src/arch/aarch64/paging.rs
+++ b/kernel/src/arch/aarch64/paging.rs
@@ -9,7 +9,7 @@ use aarch64::paging::{FrameAllocator, FrameDeallocator, Page, PhysFrame as Frame
 use aarch64::paging::memory_attribute::*;
 use log::*;
 // Depends on kernel
-use crate::consts::{KERNEL_PML4, RECURSIVE_INDEX};
+use crate::consts::RECURSIVE_INDEX;
 use crate::memory::{active_table, alloc_frame, dealloc_frame};
 
 // need 3 page
@@ -60,7 +60,7 @@ impl PageTable for ActivePageTable {
     }
 
     fn unmap(&mut self, addr: usize) {
-        let (frame, flush) = self.0.unmap(Page::of_addr(addr)).unwrap();
+        let (_frame, flush) = self.0.unmap(Page::of_addr(addr)).unwrap();
         flush.flush();
     }
 
@@ -271,15 +271,6 @@ impl InactivePageTable for InactivePageTable0 {
 }
 
 impl InactivePageTable0 {
-    fn map_kernel(&mut self) {
-        let table = unsafe { &mut *ROOT_PAGE_TABLE };
-        let e0 = table[KERNEL_PML4].clone();
-        assert!(!e0.is_unused());
-
-        self.edit(|_| {
-            table[KERNEL_PML4].set_frame(Frame::containing_address(e0.addr()), EF::default(), MairNormal::attr_value());
-        });
-    }
     /// Activate as kernel page table (TTBR0).
     /// Used in `arch::memory::remap_the_kernel()`.
     pub unsafe fn activate_as_kernel(&self) {
diff --git a/kernel/src/memory.rs b/kernel/src/memory.rs
index 7fdaa13..e985e69 100644
--- a/kernel/src/memory.rs
+++ b/kernel/src/memory.rs
@@ -1,5 +1,5 @@
 pub use crate::arch::paging::*;
-use bit_allocator::{BitAlloc, BitAlloc4K, BitAlloc64K, BitAlloc1M};
+use bit_allocator::BitAlloc;
 use crate::consts::MEMORY_OFFSET;
 use super::HEAP_ALLOCATOR;
 use ucore_memory::{*, paging::PageTable};
@@ -21,15 +21,15 @@ pub type MemorySet = ucore_memory::no_mmu::MemorySet<NoMMUSupportImpl>;
 
 // x86_64 support up to 256M memory
 #[cfg(target_arch = "x86_64")]
-pub type FrameAlloc = BitAlloc64K;
+pub type FrameAlloc = bit_allocator::BitAlloc64K;
 
 // RISCV only have 8M memory
 #[cfg(target_arch = "riscv32")]
-pub type FrameAlloc = BitAlloc4K;
+pub type FrameAlloc = bit_allocator::BitAlloc4K;
 
 // Raspberry Pi 3 has 1G memory
 #[cfg(target_arch = "aarch64")]
-pub type FrameAlloc = BitAlloc1M;
+pub type FrameAlloc = bit_allocator::BitAlloc1M;
 
 lazy_static! {
     pub static ref FRAME_ALLOCATOR: SpinNoIrqLock<FrameAlloc> = SpinNoIrqLock::new(FrameAlloc::default());