A20 enable code added

7 files changed, 284 insertions, 0 deletions

diff --git a/src/boot/boot.common.asm b/src/boot/boot.common.asm
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/src/boot/boot.common.asm
diff --git a/src/boot/boot.stage1.asm b/src/boot/boot.stage1.asm
new file mode 100644
index 0000000..801860e
--- /dev/null
+++ b/src/boot/boot.stage1.asm
@@ -0,0 +1,64 @@
+    ;; boot.stage1.asm
+
+    %include "boot.common.asm"
+    %include "boot.stage1.print.asm"
+    [org 0x7c00]    
+    [bits 16]
+
+    %define READ_SECTORS_NUM 64
+    %define BOOT_LOAD_ADDR 0x7c00
+    %define SECTOR_SIZE 512
+
+    global _start
+
+_start: 
+    ;; Disable interrupts
+    cli                         
+
+    ;; Setup segment registers
+    xor ax, ax
+    mov ds, ax
+    mov es, ax  
+    mov ss, ax
+
+    ;; Adjust Stack
+    mov sp, _start
+    
+    clc
+
+    mov si, disk_addr_packet
+    mov ah, 0x42                ; BIOS extended read function
+    mov dl, 0x80                ; Drive number
+    int 0x13                    ; BIOS disk services
+    jc _disk_read_err
+    
+    mov si, disk_read_success_msg
+    call _print_string
+
+    jmp 0x0000:0x7e00
+
+_disk_read_err: 
+    mov si, disk_read_err_msg
+    call _print_string
+
+    hlt
+    jmp _disk_read_err
+
+_end:
+    hlt 
+    jmp _end
+
+disk_read_err_msg: db "Failed to read disk", 13, 10, 0
+disk_read_success_msg: db "Read the disk successfully", 13, 10, 0
+disk_addr_packet:  
+    db 0x10
+    db 0x00
+    dw READ_SECTORS_NUM
+    dw 0x0000
+    dw 0x7e00
+    dq 1
+
+    ;; Padding and magic number
+    times 510 - ($ - $$) db 0
+    dw 0xaa55
+    
diff --git a/src/boot/boot.stage1.print.asm b/src/boot/boot.stage1.print.asm
new file mode 100644
index 0000000..aff2e0d
--- /dev/null
+++ b/src/boot/boot.stage1.print.asm
@@ -0,0 +1,21 @@
+    ;; boot.stage1.print.asm
+
+    [bits 16]
+_print_string:  
+    pusha
+    mov ah, 0x0e
+
+_print_string_loop:     
+    cmp byte [bx], 0
+    je _print_string_return
+    
+    mov al, [bx]
+    int 0x10
+    
+    inc bx 
+    jmp _print_string_loop
+
+_print_string_return:   
+    popa
+    ret
+    align 4
diff --git a/src/boot/boot.stage2.a20.asm b/src/boot/boot.stage2.a20.asm
new file mode 100644
index 0000000..6a9c250
--- /dev/null
+++ b/src/boot/boot.stage2.a20.asm
@@ -0,0 +1,147 @@
+    ;;  boot.stage2.a20.asm
+    
+_enable_a20:    
+    call _check_a20
+    test ax, ax
+    jnz .end
+
+    call _enable_a20_bios
+    call _check_a20
+    test ax, ax
+    jnz .end
+    
+    call _enable_a20_keyb
+    call _check_a20
+    test ax, ax
+    jnz .end
+
+    call _enable_a20_io92
+    call _check_a20
+    test ax, ax
+    jnz .end
+
+    .halt: hlt
+    jmp .halt
+    .end
+    ret
+
+_check_a20:     
+    pushf
+    push ds
+    push es
+    push di
+    push si
+    cli                         ; Clear Interrupts
+    
+    xor ax, ax
+    mov es, ax
+    not ax
+    mov ds, ax
+    ;; 0500 and 0510 are guaranteed to be free
+    mov di, 0x0500
+    mov si, 0x0510
+    
+    ;; Save the original values
+    mov dl, byte [es:di]
+    push dx
+    mov dl, byte [ds:si]
+    push dx
+
+    mov byte [es:di], 0x00
+    mov byte [ds:si], 0xFF
+    cmp byte [es:di], 0xFF
+
+    mov ax, 0                   ; The A20 is disabled
+    je .a20_disabled
+    mov ax, 1                   ; The A20 is enabled
+    .a20_disabled:
+    pop dx
+    mov byte [ds:si], dl
+    pop dx
+    mov byte [es:di], dl
+    
+    pop si
+    pop di
+    pop es
+    pop ds
+    popf
+    sti                         ; Enable interrupts again
+    ret
+
+_enable_a20_bios:   
+    mov ax, 0x2401
+    int 0x15
+    jc .fast_gate
+    test ah, ah
+    jnz .failed
+    call _check_a20
+    test ax, ax
+    jnz .done
+    
+    .fast_gate:
+    in al, 0x92
+    test al, 2
+    jnz .done
+    
+    or al, 2
+    and al, 0xfe
+    out 0x92, al
+   
+    call _check_a20
+    test ax, ax
+    jnz .done
+
+    .done:
+    mov ax, 1
+    ret
+
+    .failed:
+    mov ax, 0
+    ret
+
+_enable_a20_keyb:   
+    cli 
+    call .wait_io1
+    mov al, 0xad
+    out 0x64, al
+
+    call .wait_io1
+    mov al, 0x0d0
+    out 0x64, al
+
+    call .wait_io2
+    in al, 0x60
+    push eax
+
+    call .wait_io1
+    mov al, 0xd1
+    out 0x64, al
+
+    call .wait_io1
+    mov al, 0xae
+    out 0x64, al
+    
+    sti 
+    ret
+
+    .wait_io1:
+    in al, 0x64
+    test al, 2
+    jnz .wait_io1
+    ret
+    
+    .wait_io2:  
+    in al, 0x64
+    test al, 1
+    jz .wait_io2
+    ret
+
+_enable_a20_io92:   
+    in al, 0x92                 ; Read from port 0x92
+    test al, 2                  ; Check if bit 1
+    jnz .end
+    or al, 2
+    and al, 0xfe
+    out 0x92, al
+    .end
+    ret
diff --git a/src/boot/boot.stage2.asm b/src/boot/boot.stage2.asm
new file mode 100644
index 0000000..56ab73a
--- /dev/null
+++ b/src/boot/boot.stage2.asm
@@ -0,0 +1,11 @@
+    ;; boot.stage2.asm
+
+    [bits 16]
+    [org 0x7e00]
+
+    %include "boot.stage2.a20.asm"
+    %include "boot.stage2.pm.asm"
+_s2_entry:  
+    call _enable_a20
+    call _enter_pm
+    [bits 32]
diff --git a/src/boot/boot.stage2.gdt32.asm b/src/boot/boot.stage2.gdt32.asm
new file mode 100644
index 0000000..f9f27a5
--- /dev/null
+++ b/src/boot/boot.stage2.gdt32.asm
@@ -0,0 +1,29 @@
+y    ;; boot.stage2.gdt32.asm
+
+    
+GDT32:  
+    .null:
+    dd 0x0
+    dd 0x0
+    .code:
+    dw 0xffff
+    dw 0x0000
+    db 0x00
+    db 10011010b
+    db 11001111b
+    db 0x00
+    .data:
+    dw 0xffff
+    dw 0x0000
+    db 0x00
+    db 10010010b
+    db 11001111b
+    db 0x00
+GDT32_end:  
+
+GDT32_ptr:  
+    .limit: dw GDT32_end - GDT32 - 1
+    .base: dd GDT32
+
+    CODE_SEG32 equ gdt32_code_segment - gdt32_start
+    DATA_SEG32 equ gdt32_data_segment - gdt32_start
diff --git a/src/boot/boot.stage2.pm.asm b/src/boot/boot.stage2.pm.asm
new file mode 100644
index 0000000..77f5f61
--- /dev/null
+++ b/src/boot/boot.stage2.pm.asm
@@ -0,0 +1,12 @@
+    ;; boot.stage2.pm.asm
+
+
+    [bits 16]
+    %include "boot.stage2.gdt32.asm"
+
+_
+    cli
+    lgdt [GDT32_ptr]
+    
+
+    ;; Enable Protected Mode