diff --git a/ch3/os/src/boards/qemu.rs b/ch3/os/src/boards/qemu.rs
new file mode 100644
index 0000000..c2f609a
--- /dev/null
+++ b/ch3/os/src/boards/qemu.rs
@@ -0,0 +1,3 @@
+//! Constants used in rCore for qemu
+
+pub const CLOCK_FREQ: usize = 12500000;
diff --git a/ch3/os/src/config.rs b/ch3/os/src/config.rs
index 4fa0a12..aad4690 100644
--- a/ch3/os/src/config.rs
+++ b/ch3/os/src/config.rs
@@ -3,4 +3,6 @@ pub const APP_SIZE_LIMIT: usize = 0x20000;  // app的最大的二进制文件能
 pub const MAX_APP_NUM: usize = 4;  // 支持最大的用户应用数量
 
 pub const USER_STACK_SIZE: usize = 4096 * 2;  // 栈大小为8kb
-pub const KERNEL_STACK_SIZE: usize = 4096 * 2;
\ No newline at end of file
+pub const KERNEL_STACK_SIZE: usize = 4096 * 2;
+
+pub use crate::board::*;
\ No newline at end of file