; 
; Copyright 2010 Stefan Lankes, Chair for Operating Systems,
;                               RWTH Aachen University
;
; Licensed under the Apache License, Version 2.0 (the "License");
; you may not use this file except in compliance with the License.
; You may obtain a copy of the License at
;
;     http://www.apache.org/licenses/LICENSE-2.0
;
; Unless required by applicable law or agreed to in writing, software
; distributed under the License is distributed on an "AS IS" BASIS,
; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
; See the License for the specific language governing permissions and
; limitations under the License.
;
; This file is part of metalsvm.

[BITS 32]
SECTION .code
extern get_new_task
extern current_task
;extern task_table

; C prototyp:
;
; typedef struct {
;        unsigned char* top;
;        unsigned int ip;
;        tid_t id; 
;        ...
; } task_t;

; After an interrupt, the original return address has to push on the stack
; because we want to comeback...
global schedule_entry
schedule_entry:
    cli
    sub esp, 4	; add some space for the retunr address,
		; which is stored in current_task->ip

    pushfd
    pusha
    push ds
    push es
    push fs
    push gs

    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax

    ;mov eax, DWORD [current_id]
    ;shl eax, 0x4                        ; 16 = sizeof(task_t)
    ;mov edx, DWORD [eax+task_table+4]
    ;mov [esp+13*4], edx
    ;mov DWORD [eax+task_table+4], 0
    mov eax, DWORD [current_task]
    mov edx, [eax+4]
    mov DWORD [esp+13*4], edx
    mov DWORD [eax+4], 0x00

    jmp L1

; Scheduler, which switchs to the new tasks
global schedule
schedule:
    ret

    cli
    ; return address is already on the stack (via call schedule)
    pop eax
    pushfd
    push 0x08
    push eax
    push byte 0
    push byte 32
    pusha
    push ds
    push es
    push fs
    push gs

    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax

    mov eax, DWORD [current_task]
    mov [eax], esp

    ;call get_new_task

    mov DWORD [current_task], eax
    mov esp, [eax]

    pop gs
    pop fs
    pop es
    pop ds
    popa
    add esp, 8
    xor eax, eax ; return value is 0
    iret

    cli
    pushfd
    pusha
    push ds
    push es
    push fs
    push gs

    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax

    ; store current esp
    ;mov eax, DWORD [current_id]
    ;shl eax, 0x4			; 16 = sizeof(task_t)
L1:
    ;mov [eax+task_table], esp
    mov eax, DWORD [current_task]
    mov [eax], esp

    ;call get_new_task

    ; set current task and restore esp
    ;mov DWORD [current_id], eax
    ;shl eax, 0x4                        ; 16 = sizeof(task_t)
    ;mov esp, [eax+task_table]
    mov DWORD [current_task], eax
    mov esp, [eax]

    pop gs
    pop fs
    pop es
    pop ds
    popa
    popfd
    sti
    ret