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Trying to fix the boot2.asm second stage bootloader
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.vscode/launch.json
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.vscode/launch.json
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@ -8,7 +8,7 @@
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"name": "gcc-8 - Build and debug active file Level 1",
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"type": "cppdbg",
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"request": "launch",
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"program": "${fileDirname}/${fileBasenameNoExtension}",
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"program": "/home/gbowne1/Documents/ClassicOS/build/ClassicOS",
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"args": [],
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"stopAtEntry": false,
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"cwd": "${workspaceFolder}",
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@ -1,43 +1,124 @@
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[BITS 16]
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[ORG 0x0000]
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[BITS 16]
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[ORG 0x0000]
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start:
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MOV AX, CS
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MOV DS, AX
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; Initialize stack
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MOV AX, 0x0000 ; Set up a segment for the stack
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MOV SS, AX
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MOV SP, 0xFFFF
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MOV SP, 0xFFFF ; Stack grows downwards from the top of the segment
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MOV SI, msg
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JMP println
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; Copy boot sector data to a safe location
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mCopyBootSector
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JMP $
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; Load the kernel
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CALL load_kernel
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RET
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switch_to_protected_mode:
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CLI ; Disable interrupts
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LGDT [gdt_descriptor] ; Load the global descriptor table
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MOV EAX, CR0
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OR EAX, 0x1 ; Set the PE (Protection Enable) bit
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MOV CR0, EAX
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; Far jump to flush CPU queue after changing to protected mode
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JMP CODE_SEG:init_pm ; CODE_SEG is the segment selector for code segment in GDT
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init_pm:
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; Update segment registers here
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; ...
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RET
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println:
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.next_char:
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LODSB
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OR AL, AL
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JZ .stop
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MOV AH, 0x0E
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MOV BH, 0x00
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MOV BL, 0x07
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INT 0x10
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enable_a20:
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; Enable A20 gate
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cli ; Disable interrupts to prevent interference
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call a20wait ; Wait for the keyboard controller to be ready
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mov al, 0xAD ; Command to disable keyboard
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out 0x64, al ; Send command to keyboard controller command port
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call a20wait ; Wait for the keyboard controller to be ready
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mov al, 0xD0 ; Command to read output port
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out 0x64, al ; Send command to keyboard controller command port
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call a20wait ; Wait for the keyboard controller to be ready
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in al, 0x60 ; Read current state of output port
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or al, 0x02 ; Set A20 bit
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call a20wait ; Wait for the keyboard controller to be ready
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mov al, 0xD1 ; Command to write output port
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out 0x64, al ; Send command to keyboard controller command port
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call a20wait ; Wait for the keyboard controller to be ready
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mov al, 0x02 ; New output port data with A20 enabled
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out 0x60, al ; Write new output port data
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call a20wait ; Wait for the keyboard controller to be ready
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sti ; Re-enable interrupts
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ret
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JMP .next_char
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; Wait for keyboard controller to be ready
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a20wait:
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in al, 0x64 ; Read keyboard controller status port
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test al, 0x02 ; Check if input buffer is full
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jnz a20wait ; Wait until it's not full
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ret
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.stop:
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MOV AH, 0x03 ; AH = 0x03 (Get Cursor Position and Shape)
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XOR BH, BH ; BH = 0x00 (Video Page Number)
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INT 0x10 ; Call video interrupt
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; Enter kernel space and jump to the kernel entry point
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JMP 0x1000:0x0000
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INC DH
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; Code to set up flat memory model for protected mode
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; This involves setting up the segment registers with selectors
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; that point to descriptors in the GDT that define a flat memory model
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; ...
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MOV AH, 0x02 ; Set cursor position
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XOR BH, BH ; Page number
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XOR DL, DL ; Column (start from 0)
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INT 0x10 ; Call video interrupt
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RET
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; Jump to the kernel entry point
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JMP 0x1000:0x0000 ; Assuming the kernel is loaded at 0x1000:0x0000
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msg db "Second stage loaded, and Gbowne1 stinks.", 0
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; Macro to copy boot sector data to a safe location
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mCopyBootSector:
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pusha ; Save all general-purpose registers
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mov si, 0x7C00 ; Source address: where BIOS loads the boot sector
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mov di, 0x6000 ; Destination address: safe memory area
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mov cx, 512 ; Number of bytes to copy (size of boot sector)
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cld ; Clear direction flag to increment SI and DI
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copy_loop:
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lodsb ; Load byte at address DS:SI into AL, increment SI
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stosb ; Store byte from AL to address ES:DI, increment DI
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loop copy_loop ; Decrement CX; if CX != 0, repeat loop
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popa ; Restore all general-purpose registers
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ret
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; Subroutine to load the kernel
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load_kernel:
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; Disable interrupts
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cli
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; Setup disk parameters
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; ... (set CH, CL, DH, DL for LBA, set DX for drive number)
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; Calculate load address for kernel
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; ... (set ES:BX to the target memory address)
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; Read sectors from disk into memory
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mov ah, 0x02 ; Read sectors function
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mov al, 1 ; Number of sectors to read
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int 0x13 ; BIOS disk services
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; Check for read error
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jc .disk_error ; Carry flag set means an error occurred
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; Enable A20 line if necessary
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; ... (implementation depends on your system)
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; Jump to the kernel's entry point
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jmp 0x1000:0x0000 ; Assuming the kernel is loaded at 0x1000:0x0000
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.disk_error:
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; Handle disk read error
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; ... (display error message or halt)
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hlt ; Halt the system
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; Function or Subroutine to switch to protected mode
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switch_to_protected_mode:
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CLI ; Disable interrupts
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LGDT [gdt_descriptor] ; Load the global descriptor table
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MOV EAX, CR0
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OR EAX, 0x1 ; Set the PE (Protection Enable) bit
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MOV CR0, EAX
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; Far jump to flush CPU queue after changing to protected mode
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JMP CODE_SEG:init_pm ; CODE_SEG is the segment selector for code segment in GDT
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@ -1,17 +1,15 @@
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#include "cpu.h"
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// Function to read a 32-bit value from a CPU register
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uint32_t read_register(uint8_t reg)
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{
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uint32_t read_register(uint8_t reg) {
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uint32_t value;
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__asm__ volatile("mov %0, %%" + reg : "=r"(value));
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__asm__ volatile("mov %0, %%" : "+r"(value) : "c"(reg));
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return value;
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}
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// Function to write a 32-bit value to a CPU register
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void write_register(uint8_t reg, uint32_t value)
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{
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__asm__ volatile("mov %0, %%" + reg : : "r"(value));
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void write_register(uint8_t reg, uint32_t value) {
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__asm__ volatile("mov %0, %%" : : "c"(reg), "r"(value));
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}
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// Function to read the value of the CR0 register
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