#define ASM_SOURCE 1
#include "segment.h"
.file "irq_pit.S"

.text

.extern switchKthread

.globl pit_handler
.type pit_handler, @function
pit_handler:         // already got eflags, cs and eip on stack thanks to CPU 
  pushl $0           // err_code     esp+12+7*4=40
  pushl %ebp
  movl %esp, %ebp

  pushl %eax
  pushl %ecx
  pushl %edx
  pushl %ebx
  pushl %esi
  pushl %edi
  subl $2, %esp      // (alignment)  esp+10
  pushw %ss          //              esp+8
  pushw %ds          //              esp+6
  pushw %es          //              esp+4
  pushw %fs          //              esp+2
  pushw %gs          //              esp

  /* Set correct kernel segment descriptors' value */
  movw $BUILD_SEGMENT_REG_VALUE(0, 0, SEG_KDATA), %di
  pushw %di ; popw %ds
  pushw %di ; popw %es
  pushw %di ; popw %fs
  pushw %di ; popw %gs

  /* Send EOI to PIC */
  movb  $0x20, %al
  outb  %al, $0x20

  pushl %esp
  call pitIrqHandler
  addl $4, %esp
  movl %eax,%esp

  /* Restore the CPU context */
  popw %gs
  popw %fs
  popw %es
  popw %ds
  popw %ss
  addl $2,%esp
  popl %edi
  popl %esi
  popl %ebx
  popl %edx
  popl %ecx
  popl %eax
  popl %ebp
  addl $4, %esp /* Ignore "error code" */

  /* This restores the eflags, the cs and the eip registers */
  iret /* equivalent to: popfl ; ret */