1 files changed, 59 insertions, 0 deletions
diff --git a/asm/pit.s b/asm/pit.s
new file mode 100644
index 0000000..ab8dcdb
--- /dev/null
+++ b/asm/pit.s
@@ -0,0 +1,59 @@
+.global pit_init
+.global pit_interrupt_handler
+.global pit_get_ticks
+
+ticks:
+.int 0
+
+pit_get_ticks:
+    
+    mov (ticks),%eax
+    ret
+
+pit_interrupt_handler:
+
+    // increase tick counter
+    push %eax
+    mov $ticks, %eax
+    incl (%eax)
+    pop %eax
+
+    ////
+
+    pusha          //Push all standard registers
+
+    mov %esp, %eax	//save current stack pointer (pointing to registers!)
+
+    movl $stack_top, %esp	//use stack from multiboot.s(16Kb)
+
+    // call our scheduler passing it the old stack addres (pointing to pushed registers (pusha))
+    push %eax   
+    call task_switch_next 
+
+    // the scheduler returned the new stack pointer (after taskswitch)
+    mov %eax, %esp   //Replace the stack with what the C code gave us
+
+    // acknowlege irq
+    mov $0x20,%al   
+    out %al,$0x20   
+    
+    popa           //Put the standard registers back
+
+    iret
+
+pit_init:
+
+    // configure ticking 25 times a second
+    // 1193180 / 25 = 47727.2
+    mov $47727, %dx
+
+    mov $0b00110100, %al
+    outb %al,$0x43
+
+    mov %dx,%ax
+
+    out %al, $0x40
+    xchg %ah,%al
+    out %al, $0x40
+
+    ret