sys_yield tests worked on qemu.

user/Makefile

@@ -18,4 +18,6 @@ binary: elf
 build: binary
 
 clean:
-	@cargo clean
+	@cargo clean
+
+.PHONY: elf binary build clean

user/src/bin/00write_a.rs

@@ -6,11 +6,14 @@ extern crate user_lib;
 
 use user_lib::sys_yield;
 
+const WIDTH: usize = 10;
+const HEIGHT: usize = 5;
+
 #[no_mangle]
 fn main() -> i32 {
-    for _ in 0..3 {
-        for _ in 0..10 { print!("A"); }
-        println!("");
+    for i in 0..HEIGHT {
+        for _ in 0..WIDTH { print!("A"); }
+        println!(" [{}/{}]", i + 1, HEIGHT);
         sys_yield();
     }
     println!("Test write_a OK!");

user/src/bin/01write_b.rs

@@ -6,13 +6,16 @@ extern crate user_lib;
 
 use user_lib::sys_yield;
 
+const WIDTH: usize = 10;
+const HEIGHT: usize = 2;
+
 #[no_mangle]
 fn main() -> i32 {
-    for _ in 0..3 {
-        for _ in 0..10 { print!("B"); }
-        println!("");
+    for i in 0..HEIGHT {
+        for _ in 0..WIDTH { print!("B"); }
+        println!(" [{}/{}]", i + 1, HEIGHT);
         sys_yield();
     }
     println!("Test write_b OK!");
     0
-}
+}

user/src/bin/02write_c.rs

@@ -6,13 +6,16 @@ extern crate user_lib;
 
 use user_lib::sys_yield;
 
+const WIDTH: usize = 10;
+const HEIGHT: usize = 3;
+
 #[no_mangle]
 fn main() -> i32 {
-    for _ in 0..3 {
-        for _ in 0..10 { print!("C"); }
-        println!("");
+    for i in 0..HEIGHT {
+        for _ in 0..WIDTH { print!("C"); }
+        println!(" [{}/{}]", i + 1, HEIGHT);
         sys_yield();
     }
     println!("Test write_c OK!");
     0
-}
+}