Started working on multistage bootloader. Added VBE data in stage2.asm

2024-04-17 17:23:09 +02:00
parent bc6b0ec292
commit 052b668d98
7 changed files with 303 additions and 166 deletions
@@ -0,0 +1,158 @@
+[bits 16]
+[org 0x7e00]
+
+%define KERNEL_LOC 0x1000
+
+start:
+    mov [driveNum], dl
+
+;; Load the global descriptor table (GDT)
+loadGDT:
+    cli
+    lgdt [GDT_Descriptor]
+    ; Enable protected mode
+    mov eax, cr0
+    or eax, 1
+    mov cr0, eax
+
+    ; Far jump to 32 bit mode!!
+    jmp CODE_SEG:protected_start
+
+;; 32 Bit entry code
+[bits 32]
+protected_start:
+    ; Set up data and stack segments
+    mov ax, DATA_SEG 
+    mov ds, ax 
+    mov ss, ax 
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    
+    ; Set up the stack pointer in protected mode
+    mov ebp, 0x90000
+    mov esp, ebp
+
+    ; Perform The far jump
+    mov al, [driveNum]
+    push ax
+    
+    jmp CODE_SEG:KERNEL_LOC
+
+;; Data
+driveNum: db 0
+
+;; GDT
+GDT:
+.start:
+    .nullDescriptor:    ; No clue why this exists
+        dd 0
+        dd 0
+    .codeDescriptor:    ; Memory for code
+        dw 0xffff       ; First 16 bits of limit
+        dw 0            ; 16 bits +
+        db 0            ; + 8 bits = 24 bits
+        db 0b10011010   ; p, dpl, s, type flags
+        db 0b11001111   ; Other flags, last 4 bits of limit
+        db 0            ; Base
+    .dataDescriptor:    ; Memory for data
+        dw 0xffff       ; First 16 bits of limit
+        dw 0            ; 16 bits +
+        db 0            ; + 8 bits = 24 bits
+        db 0b10010010   ; p, dpl, s, type flags
+        db 0b11001111   ; Other flags, last 4 bits of limit
+        db 0            ; Base
+.end:
+
+GDT_Descriptor:
+    dw GDT.end - GDT.start - 1  ; Size
+    dd GDT.start        ; GDT Pointer
+
+CODE_SEG equ GDT.codeDescriptor - GDT.start
+DATA_SEG equ GDT.dataDescriptor - GDT.start
+
+;; VBE Stuff
+width: dw 1920
+height: dw 1080
+bpp: db 32
+offset: dw 0
+_segment: dw 0 ; segment is a keyword
+mode: dw 0
+
+times 512-($-$$) db 0 ; End Sector 1
+
+;; Sector 2
+vbeInfoBlock:
+    .vbeSigniture: db "VBE2"
+    .vbeVersion: dw 0x0300 ; BCD Version
+    .oemStringPtr: dd 0
+    .capibilities: dd 0
+    .videoModePtr: dd 0
+    .totalMemory: dw 0
+    .oemSoftwareRev: dw 0
+    .oemVendorNamePtr: dd 0
+    .oemProductNamePtr: dd 0
+    .oemProductRevisionPtr: dd 0
+    .reserved: times 222 db 0
+    .oemData: times 256 db 0
+
+;; Sector 3
+modeInfoBlock:
+;; Required by all VBE revisions
+    .modeAttr: dw 0
+    .windowAAtrr: db 0
+    .windowBAttr: db 0
+    .windowGranularity: dw 0
+    .windowSize: dw 0
+    .windowASegment: dw 0
+    .windowBSegment: dw 0
+    .windowFunctionPtr: dd 0
+    .bytesPerScanline: dw 0
+
+;; Required by VBE 1.2+
+    .xRes: dw 0
+    .yRex: dw 0
+    .xCharSize: db 0
+    .yCharSize: db 0
+    .planeCount: db 0
+    .bpp: db 0
+    .bankCount: db 0
+    .memoryModel: db 0
+    .bankSize: db 0
+    .imagePageCount: db 0
+    .reserved1: db 1
+
+;; Direct color fields
+    .redMaskSize: db 0
+    .redFieldPos: db 0
+    .greenMaskSize: db 0
+    .greenFieldPos: db 0
+    .blueMaskSize: db 0
+    .blueFieldPos: db 0
+    .reservedMaskSize: db 0
+    .reservedFieldPos: db 0
+    .directColorModeInfo: db 0
+
+;; Required by VBE 2.0+
+    .physicalAddressPtr: dd 0
+    .reserved2: db 0
+    .reserved3: db 0
+
+;; Required by VBE 3.0+
+    .linearBytesPerScanline: dw 0
+    .bankImagePageCount: db 0
+    .linearImagePageCount: db 0
+    .linearRedMaskSize: db 0
+    .linearRedFieldPos: db 0
+    .linearGreenMaskSize: db 0
+    .linearGreenFieldPos: db 0
+    .linearBlueMaskSize: db 0
+    .linearBlueFieldPos: db 0
+    .linearReservedMaskSize: db 0
+    .linearReservedFieldPos: db 0
+    .maxPixelClock: dd 0
+
+    .reserved4: times 190 db 0 
+
+times (512*3)-($-$$) db 0 ; 2 Pad out to 3 sectors
+