Merge pull request #15 from E-Almqvist/dev

32bit Protected Mode

src/bootloader.asm

@@ -6,26 +6,8 @@
 	mov bp, 0x8000 ; move it to 0x8000
 	mov sp, bp
 
-	; Print the welcome string
-	mov bx, welcome_string
-	call println
-
-	; Read second sector (outside bootsector)
-	mov bx, 0x9000			; LOAD LOCATION 
-	mov dh, 2			; SECTOR-COUNT
-	mov dl, [BOOT_DRIVE]		; DISK-INDEX
-	call disk_read
-
-
-	; Print out whatever bloated data that was read
-	mov dx, [0x9000]
-	call print_hex
-
-	mov bx, [ASCII_END]
-	call println
-
-	mov dx, [0x9000 + 512] ; read from second sector too
-	call print_hex
+	; Switching to PM
+	call pm_preinit
 
 	jmp $  ; inf loop
 
@@ -33,8 +15,13 @@
 %include "bios.asm"
 %include "pm.asm"
 
-; Data
-welcome_string:	db "e Operating-System (eOS)", ASCII_CARRIAGE_RETURN, ASCII_LINEBREAK, "Version 2021 0.0", ASCII_END
+BEGIN_PM:
+	mov ebx, welcome_string
+	call vga_print
+
+	jmp $
+
+welcome_string:	db "e Operating-System (eOS): Version 2021 0.0", ASCII_END
 BOOT_DRIVE: db 0
 
 ; Bootsector

src/pm.asm

@@ -1,2 +1,37 @@
-%include "equ/vga.asm"
+; Utils
+%include "equ/vga.asm" 
 %include "pm/vga/print.asm" 
+
+; GDT & switching to PM
+%include "pm/gdt.asm" 	; GDT defined here
+
+; Switching to PM
+[bits 16]
+pm_preinit:
+	cli			; Switch interupts
+
+	lgdt [gdt_descriptor] 	; Tell the CPU about the GDT
+
+	mov eax, cr0		; Set first bit of the CR0 register
+	or eax, 0x1		; to 1
+	mov cr0, eax		; Update the control register
+
+	; Initialize PM
+	jmp GDT_CODE_SEG:pm_init	
+
+[bits 32]
+; Init registers & stack when in PM
+pm_init:
+	mov ax, GDT_DATA_SEG	; Point the segment registers to GDT_DATA_SEG
+	; Segment registers
+	mov ds, ax
+	mov ss, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+
+	mov ebp, 0x900000	; Update the stack pointer
+	mov esp, ebp
+
+	call BEGIN_PM
+

src/pm/gdt.asm

@@ -0,0 +1,43 @@
+; GDT
+
+gdt_start:
+
+gdt_null:		; NULL descriptor
+	dd 0x0		; 4-bytes of 
+	dd 0x0		; 0x0 (0) = NULL
+
+gdt_code: 		; Code SD
+	; Range: 	0x0 - 0xfffff
+	; Flags1: 	1001b (present:2 privilege:descriptor type)
+	; Type:		1010b (code:conforming:readable:accessed)
+	; Flags2:	1100b (granularity:32bit default:64bit seg:AVL)
+
+	dw 0xffff	; Limit (bits 0-15)
+	dw 0x0		; Base (bits 0-15)
+	db 0x0		; Base (bits 16-23)
+	db 10011010b 	; Flags1 : Type
+	db 11001111b	; Flags2 : Limit (16-19)
+	db 0x0		; Base (bits 24-31)
+
+gdt_data: 		; Data SD
+	; Same flags as gdt_code but different type flags
+	; Type: 	0010b (code:expand dowm:writable:accessed)
+
+	dw 0xffff	; Limit (bits 0-15)
+	dw 0x0		; Base (bits 0-15)
+	db 0x0		; Base (bits 16-23)
+	db 10010010b 	; Flags1 : Type
+	db 11001111b	; Flags2 : Limit (16-19)
+	db 0x0		; Base (bits 24-31)
+
+gdt_end:		; Mark the end so we can get the delta-memory (size of GDT)
+
+; GDT descriptor
+gdt_descriptor:
+	dw gdt_end - gdt_start - 1	; Size of GDT is always -1 of actual size (WHY?!?!?!?!??!)
+	dd gdt_start			; Pointer to the GDT
+
+
+; Lazy constants
+GDT_CODE_SEG equ gdt_code - gdt_start
+GDT_DATA_SEG equ gdt_data - gdt_start