userspace and kernelspace taskswitching

1 files changed, 28 insertions, 22 deletions

diff --git a/asm/pit.s b/asm/pit.s
index ab8dcdb..c25e9a1 100644
--- a/asm/pit.s
+++ b/asm/pit.s
@@ -12,32 +12,38 @@ pit_get_ticks:
 
 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)
+    push %eax // persist
 
-    // 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
+    // INC TICK COUNTER
+    mov $ticks, %eax    
+    incl (%eax)
 
-    // acknowlege irq
-    mov $0x20,%al   
+    // ACK IRQ
+    mov $0x20,%al
     out %al,$0x20   
+
+    pop %eax // load original
     
-    popa           //Put the standard registers back
+    ///////
+
+    pusha          //Push all standard registers
+    push %ds       //Push data segment
+    push %es       //etc...
+    push %fs
+    push %gs
+
+    mov %esp, %eax          // remember current %esp
+    movl $stack_top, %esp   // switch to our small scheduler stack
+
+    push %eax               // set original %esp as param and... 
+    call task_switch_next   // call scheduler
+    mov  %eax, %esp         // use %esp we got from scheduler
+
+    pop %gs
+    pop %fs
+    pop %es
+    pop %ds
+    popa           
 
     iret