Initial kernel work
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Nocturn9x
parent
aa830de9c2
commit
c06dbb7280
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@ -68,4 +68,5 @@ _deps
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# TSOS stuff
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*.bin
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dist/
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dist/
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@ -3,124 +3,64 @@
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; do some basic setup and then call into the kernel
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[org 0x7c00] ; Address where the code expects to be loaded in. The BIOS always loads us here
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kernel_offset: equ 0x1000
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; We save the value of the current boot drive
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mov [boot_drive], dl
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; Now we setup the stack by setting the
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; base pointer to address 0x8000. The address
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; itself doesn't matter as long as it's far
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; enough away from memory already in use by
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; the BIOS
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mov bp, 0x9000
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mov sp, bp
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call bios_cls
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mov si, real_mode_msg
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call bios_println
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call load_kernel
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call switch_to_protected_mode
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jmp $ ; Keeps jumping at the current address (loops forever)
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; Now we include our "function definitions" (after the
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; loop, so they're never executed unless explicitly called)
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%include "src/bootloader/util/disk.s"
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%include "src/bootloader/util/io.s"
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%include "src/bootloader/gdt.s"
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%include "src/bootloader/switch32.s"
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[bits 16] ; All x86 CPUs start in 16 bit (aka "real") mode, so we tell nasm to emit 16-bit code
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load_kernel: ; Loads the kernel into memory
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mov si, loading_kernel_msg
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call bios_println
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mov bx, kernel_offset
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mov dh, 1
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mov dl, [boot_drive]
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call load_disk
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ret
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; Here we define our variables: They need to be defined after the
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; halting because otherwise they will be executed as code
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real_mode_msg: db "Booted in real mode", 0
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protected_mode_msg: db "Switched to protected mode", 0
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loading_kernel_msg: db "Loading kernel", 0
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boot_drive: db 0
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start:
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; Copied from https://github.com/limine-bootloader/limine/blob/trunk/stage1/hdd/bootsect.asm.
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; Quote:
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; Some BIOSes will do a funny and decide to overwrite bytes of code in
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; the section where a FAT BPB would be, potentially overwriting
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; bootsector code. Avoid that by filling the BPB area with dummy values.
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; Some of the values have to be set to certain values in order to boot
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; on even quirkier machines.
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; Source: https://github.com/freebsd/freebsd-src/blob/82a21151cf1d7a3e9e95b9edbbf74ac10f386d6a/stand/i386/boot2/boot1.S
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jmp skip_bpb
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nop
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bpb:
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times 3-($-$$) db 0
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.bpb_oem_id: db "TSOS "
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.bpb_sector_size: dw 512
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.bpb_sects_per_cluster: db 0
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.bpb_reserved_sects: dw 0
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.bpb_fat_count: db 0
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.bpb_root_dir_entries: dw 0
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.bpb_sector_count: dw 0
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.bpb_media_type: db 0
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.bpb_sects_per_fat: dw 0
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.bpb_sects_per_track: dw 18
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.bpb_heads_count: dw 2
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.bpb_hidden_sects: dd 0
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.bpb_sector_count_big: dd 0
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.bpb_drive_num: db 0
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.bpb_reserved: db 0
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.bpb_signature: db 0
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.bpb_volume_id: dd 0
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.bpb_volume_label: db "TSOS "
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.bpb_filesystem_type: times 8 db 0
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; The skip_bpb and initialize_cs code is adapted
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; from the Limine bootloader as well
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skip_bpb:
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cli
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cld
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jmp 0x0000:initialise_cs
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initialise_cs:
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xor si, si
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mov ds, si
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mov es, si
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mov ss, si
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sti
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; We're not made for floppy disks, these are dead anyways.
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; So if the value the BIOS passed is <0x80, just assume it has passed
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; an incorrect value.
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cmp dl, 0x80
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jb invalid_boot_device
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; Values above 0x8f are dubious so we assume we weren't booted properly
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; for those either
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cmp dl, 0x8f
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ja invalid_boot_device
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continue:
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; First off, we setup the stack by setting the
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; base pointer to address 0x8000. The address
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; itself doesn't matter as long as it's far
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; enough away from memory already in use by
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; the BIOS
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mov bp, 0x8000
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mov sp, bp ; The stack starts out empty, so sp == bp
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[bits 32]
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BEGIN_32BIT: ; After the switch we will get here
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mov esi, protected_mode_msg
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; My modified print function takes an offset
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; to add to the start of the video memory that
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; is added before writing. We skip the first
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; 320 bytes so that we don't overwrite the log
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; messages we may have written beforehand
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mov ecx, 0x140
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call vga_println
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call kernel_offset
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jmp $
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; Since we have a stack, we can now call functions,
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; so we print a simple startup message using BIOS
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; routines
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mov si, startup_msg
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call bios_print
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; We also inform the user we're loading a few
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; sectors from the boot drive
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mov si, disk_read_info
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and dx, 0xff ; Gets rid of the high 8 bits of dx so
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; we only print the hex value of dh,
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; which is the type of storage device
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; we're booting from (0 = floppy,
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; 1 = floppy2, 0x80 = hdd, 0x81 = hdd2)
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call bios_print
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call bios_printh
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call bios_newline
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; We load data from the current boot drive. The data is copied
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; to memory starting at address 0x9000
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mov bx, 0x9000
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mov dh, 2 ; Read 3 sectors (2 for our dummy sectors, 1 for our variables)
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; The dl register is already set by the BIOS
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call load_disk
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; Now we retrieve the test data we placed in the other
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; sectors and print it in hexadecimal format
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mov dx, [0x9000]
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call bios_printh ; Should print 0xDADA
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call bios_newline
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mov dx, [0x9000 + 512]
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call bios_printh ; Should print OxFACE
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endless_loop:
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jmp $ ; Keeps jumping at the current address (loops forever)
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invalid_boot_device:
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mov si, invalid_boot_device_msg
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call bios_println
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; Now we include our "function definitions" (after the
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; loop, so they're never executed unless explicitly called)
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%include "src/bootloader/util/disk.s"
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%include "src/bootloader/util/io.s"
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; Here we define our variables: They need to be defined after the
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; halting because otherwise they will be executed as code
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startup_msg: db "TSOS is starting up", 0xA, 0xD, 0
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invalid_boot_device_msg: db "Invalid boot device", 0
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; padding and magic number
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; Padding and magic number
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times 510 - ($-$$) db 0
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dw 0xaa55
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; We add more sectors to our binary so we can read them
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times 256 dw 0xdada ; sector 2 = 512 bytes
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times 256 dw 0xface ; sector 3 = 512 bytes
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@ -43,6 +43,5 @@ disk_loop:
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jmp $
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disk_read_info: db "Booting from disk type ", 0
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disk_read_error_msg: db "Read error: ", 0
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disk_sectors_error_msg: db "Read error (wrong number of sectors)", 0
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disk_sectors_error_msg: db "Sector read count error", 0
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@ -97,6 +97,14 @@ bios_printh:
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popa
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ret
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bios_cls:
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pusha
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mov ah, 0x00
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mov al, 0x03 ; text mode 80x25 16 colours
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int 0x10
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popa
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ret
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HEX_OUT: db '0x0000', 0 ; reserve memory for our new string
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@ -108,23 +116,24 @@ VMEM_START: equ 0xb8000 ; Video memory always starts at this address
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; the first byte is the ASCII codepoint to be printed, while the next
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; octet represents additional formatting information (color, blink,
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; underline, etc.). More info: https://en.wikipedia.org/wiki/VGA_text_mode
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WHITE_ON_BLACK: equ 0x0f
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TEXT_COLOR: equ 0x07
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vga_print:
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; Prints a null-terminated string located
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; on the esi register
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; on the esi register. Offsets the write
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; by ecx bytes
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pusha
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mov edx, VMEM_START
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add edx, ecx
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vga_print_loop:
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mov al, [esi]
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mov ah, WHITE_ON_BLACK
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mov ah, TEXT_COLOR
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cmp al, 0
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je vga_print_done ; If we're at the null byte, we exit
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mov [edx], ax ; Write the 2-byte character to video memory
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inc esi ; Go to the next character in the string
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add ebx, 2 ; Go to the next character in video memory
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add edx, 2 ; Go to the next character in video memory
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jmp vga_print_loop
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vga_print_done:
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@ -137,8 +146,8 @@ vga_println:
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; esi register and terminates it with a newline
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pusha
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call vga_print
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mov esi, NEWLINE
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call vga_print
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;mov esi, NEWLINE
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;call vga_print
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popa
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ret
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