Merge pull request #473 hardware-interrupts

Cargo.toml

@@ -9,6 +9,7 @@ spin = "0.4.6"
 volatile = "0.2.3"
 uart_16550 = "0.1.0"
 x86_64 = "0.2.8"
+pic8259_simple = "0.1.1"
 
 [dependencies.lazy_static]
 version = "1.0"

blog/content/second-edition/posts/08-hardware-interrupts/index.md

@@ -102,7 +102,7 @@ pub mod interrupts;
 
 // in src/interrupts.rs
 
-use pic8259::ChainedPics;
+use pic8259_simple::ChainedPics;
 use spin;
 
 pub const PIC_1_OFFSET: u8 = 32;
@@ -165,7 +165,7 @@ pub extern "C" fn _start() -> ! {
 
 The `interrupts::enable` function of the `x86_64` crate executes the special `sti` instruction (“set interrupts”) to enable external interrupts. When we try `bootimage run` now, we see that a double fault occurs:
 
-TODO screenshot
+![QEMU printing `EXCEPTION: DOUBLE FAULT` because of hardware timer](qemu-hardware-timer-double-fault.png)
 
 The reason for this double fault is that the hardware timer (the [Intel 8253] to be exact) is enabled by default, so we start receiving timer interrupts as soon as we enable interrupts. Since we didn't define a handler function for it yet, our double fault handler is invoked.
 
@@ -208,7 +208,7 @@ We introduce a `TIMER_INTERRUPT_ID` constant to keep things organized. Our `time
 
 In our timer interrupt handler, we print a dot to the screen. As the timer interrupt happens periodically, we would expect to see a dot appearing on each timer tick. However, when we run it we see that only a single dot is printed:
 
-TODO screenshot
+![QEMU printing only a single dot for hardware timer](qemu-single-dot-printed.png)
 
 ### End of Interrupt
 
@@ -233,7 +233,7 @@ We need to be careful to use the correct interrupt vector number, otherwise we c
 
 When we now execute `bootimage run` we see dots periodically appearing on the screen:
 
-TODO screenshot gif
+![QEMU printing consequtive dots showing the hardware timer](qemu-hardware-timer-dots.gif)
 
 ### Configuring The Timer
 

src/interrupts.rs

@@ -0,0 +1,10 @@
+use pic8259_simple::ChainedPics;
+use spin;
+
+pub const PIC_1_OFFSET: u8 = 32;
+pub const PIC_2_OFFSET: u8 = PIC_1_OFFSET + 8;
+
+pub static PICS: spin::Mutex<ChainedPics> =
+    spin::Mutex::new(unsafe { ChainedPics::new(PIC_1_OFFSET, PIC_2_OFFSET) });
+
+pub const TIMER_INTERRUPT_ID: u8 = PIC_1_OFFSET;

src/lib.rs

@@ -5,6 +5,7 @@ extern crate spin;
 extern crate volatile;
 #[macro_use]
 extern crate lazy_static;
+extern crate pic8259_simple;
 extern crate uart_16550;
 extern crate x86_64;
 
@@ -14,6 +15,7 @@ extern crate array_init;
 extern crate std;
 
 pub mod gdt;
+pub mod interrupts;
 pub mod serial;
 pub mod vga_buffer;
 

src/main.rs

@@ -10,6 +10,7 @@ extern crate x86_64;
 extern crate lazy_static;
 
 use core::panic::PanicInfo;
+use blog_os::interrupts::{self, PICS};
 
 /// This function is the entry point, since the linker looks for a function
 /// named `_start` by default.
@@ -20,13 +21,8 @@ pub extern "C" fn _start() -> ! {
 
     blog_os::gdt::init();
     init_idt();
-
-    fn stack_overflow() {
-        stack_overflow(); // for each recursion, the return address is pushed
-    }
-
-    // trigger a stack overflow
-    stack_overflow();
+    unsafe { PICS.lock().initialize() };
+    x86_64::instructions::interrupts::enable();
 
     println!("It did not crash!");
     loop {}
@@ -52,6 +48,9 @@ lazy_static! {
                 .set_stack_index(blog_os::gdt::DOUBLE_FAULT_IST_INDEX);
         }
 
+        let timer_interrupt_id = usize::from(interrupts::TIMER_INTERRUPT_ID);
+        idt[timer_interrupt_id].set_handler_fn(timer_interrupt_handler);
+
         idt
     };
 }
@@ -71,3 +70,11 @@ extern "x86-interrupt" fn double_fault_handler(
     println!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
     loop {}
 }
+
+extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut ExceptionStackFrame) {
+    print!(".");
+    unsafe {
+        PICS.lock()
+            .notify_end_of_interrupt(interrupts::TIMER_INTERRUPT_ID)
+    }
+}