diff options
Diffstat (limited to 'src/bootloader.asm')
| -rw-r--r-- | src/bootloader.asm | 277 |
1 files changed, 0 insertions, 277 deletions
diff --git a/src/bootloader.asm b/src/bootloader.asm deleted file mode 100644 index f18750c..0000000 --- a/src/bootloader.asm +++ /dev/null @@ -1,277 +0,0 @@ -;Copyright 2019 Benji Dial - -;Permission to use, copy, modify, and/or distribute this -;software for any purpose with or without fee is hereby -;granted, provided that the above copyright notice and this -;permission notice appear in all copies. - -;THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS -;ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL -;IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO -;EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, -;INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES -;WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, -;WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER -;TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE -;USE OR PERFORMANCE OF THIS SOFTWARE. - -kload equ 0x0010_0000 - -global_info:;0x0500 - 0x05ff (0x0515) -.fat equ 0x0500;dword - pointer -.root_dir equ 0x0504;dword - pointer -.low_mem equ 0x0508;word - usable memory from 0 to 1MiB in kiB -.mid_mem equ 0x050a;word - usable memory from 1MiB to 16MiB in kiB -.mem_used equ 0x050c;word - used memory from 0 to 1MiB in kiB -.kernel_s equ 0x050e;word - kernel image length in kiB - ;dword - kernel use -.high_mem equ 0x0514;word - usable memory from 16MiB up in 64s of kiB - -fat_header:;0x7c03 - 0x7c3d -.oem_name equ 0x7c03;mkfs.fat - -.bytes_per_sector equ 0x7c0b;0x0200 - -.sectors_per_cluster equ 0x7c0d;0x01 - -.reserved_sectors equ 0x7c0e;0x0002 - handled -.n_fats equ 0x7c10;0x01 - -.root_dir_entries equ 0x7c11; - -.n_sectors equ 0x7c13;0x0b40 - -.media_type equ 0x7c15; - -.sectors_per_fat equ 0x7c16; - handled -.sectors_per_track equ 0x7c18;0x0012 - -.sides equ 0x7c1a;0x0002 - -.hidden_sectors equ 0x7c1c;0x0000_0000 - -.long_sectors equ 0x7c20;0x0000_0000 - -.drive_number equ 0x7c24; - ignored, used as scratch for real drive number -.flags equ 0x7c25; - -.signature equ 0x7c26;0x29 - errors on other values -.id equ 0x7c27; - -.label equ 0x7c2b;PORTLAND OS - -.fs_type equ 0x7c36;FAT12 - errors on other values - -error_codes: -.bad_fat_header equ 0o000 -.insufficient_memory equ 0o001 -.no_kernel equ 0o002 -.kernel_too_big equ 0o003 - -org 0x7c3e -bits 16 - - ;Enable A20 line - in al, 0x92 - or al, 0x02 - out 0x92, al - - ;Load second sector of bootloader - mov ah, 0x42 - mov si, dap - int 0x13 - - ;Check FAT signature - test byte [fat_header.signature], 0x29 - jne bad_fat_header - test word [fat_header.fs_type], 0x4146;FA - jne bad_fat_header - test word [fat_header.fs_type + 2], 0x3154;T1 - jne bad_fat_header - test word [fat_header.fs_type + 4], 0x2032;2 - jne bad_fat_header - test word [fat_header.fs_type + 6], 0x2020; - jne bad_fat_header - - ;Store boot drive ID for later - mov byte [fat_header.drive_number], dl - -memory: - ;Get available low memory - int 0x12 - mov word [global_info.low_mem], ax - mov word [global_info.mem_used], 0x0020 - - ;Get available mid and high memory - xor dx, dx - mov ax, 0xe801 - int 0x15 - test dx, dx - jnz .got - mov cx, ax - mov dx, bx -.got: - mov word [global_info.mid_mem], cx - mov word [global_info.high_mem], dx - - ;Load FAT - mov ax, word [fat_header.reserved_sectors] - mov word [dap.start], ax - xor eax, eax - mov ax, word [fat_header.sectors_per_fat] - call load_low - mov dword [global_info.fat], ebx - -load_root: - ;Load root directory - mov ax, word [fat_header.sectors_per_fat] - xor dh, dh - mov dl, word [fat_header.n_fats] - mul dx - add ax, [fat_header.reserved_sectors] - jnc .no_inc - inc dx -.no_inc: - mov word [dap.start], ax - mov word [dap.start + 2], dx - mov ax, word [fat_header.root_dir_entries] - shr ax, 4 - call load_low - mov dword [global_info.root_dir], ebx - - ;Calculate end of root directory - xor ecx, ecx - mov cx, word [fat_header.root_dir_entries] - shl ecx, 5 - add ecx, ebx - jc insufficient_memory - -find_kernel: - mov eax, 0x6e72_656b;kern - mov edx, 0x2020_6c65;el -.loop: - ;Check name - test dword [ebx], eax - jne .next - test dword [ebx + 4], edx - jne .next - test word [ebx + 8], 0x7973;sy - jne .next - test byte [ebx + 10], 0x73;s - je .found -.next: - ;Next record - add ebx, 32 - test ebx, ecx - jne .loop - - ;Got to end of directory - mov dl, error_codes.no_kernel - jmp error - - ;ebx is pointer to entry - ;word [ebx + 26] is first cluster - ;dword [ebx + 28] is size -.found: - ;Save size for later - mov eax, dword [ebx + 28] - shr eax, 10 - test eax, 0x003f_0000 - jz .store_size - mov dl, error_codes.kernel_too_big - jmp error -.store_size: - mov word [global_info.kernel_s], ax - - ;Save sector number for later - mov cx, [ebx + 26] - - ;find 1kiB buffer - mov ax, 2 - mov byte [load_low.ret_with_segment], 0xc3;ret - call load_low - shl ebx, 4 - -load_kernel: - - -load_low: - ;ax in : number of sectors - ;qword [dap.start] in : starting sector - - ;Store length in DAP - mov word [dap.length], ax - - ;Calculate kiB used - dec ax - shr ax, 1 - inc ax - mov dx, ax - add ax, word [global_info.mem_usage] - - ;Fail if not enough is available - jc insufficient_memory - cmp ax, word [global_info.low_mem] - jg insufficient_memory - - ;Check if address will fit in DAP - test ah, ah - jnz insufficient_memory - - ;Commit usage - mov word [global_info.low_mem_usage], ax - - ;Put address into DAP - xor ebx, ebx - mov bh, al - shr bx, 2 - mov word [dap.segment], bx - mov word [dap.offset], 0x0000 -.ret_with_segment: - - ;Load from disk - mov si, dap - mov ah, 0x42 - int 0x13 - shl ebx, 4 - ret - -bad_fat_header: - mov dl, error_codes.bad_fat_header - jmp error - -insufficient_memory: - mov dl, error_codes.insufficient_memory - jmp error - -error: - ;Print error code (in octal) - mov ax, 0xb800 - mov ds, ax - mov word [0], 0x0f72;E - mov ax, 0x0f00 - mov al, dl - and al, 0x07 - or al, 0x30 - mov word [6], ax;bottom digit - shr dl, 3 - mov al, dl - and al, 0x07 - or al, 0x30 - mov word [4], ax;middle digit - shr dl, 3 - mov al, dl - or al, 0x30 - mov word [2], ax;top digit - - cli -.halt: - hlt - jmp .halt - -gdt: -dw 0x28 -dd gdt + 6 -dq 0x0000_0000_0000_0000 -dq 0x0040_9a00_0000_7fff;0x000000 - 0x007fff -dq 0x0040_9200_0000_7fff -dq 0x00c0_9a00_8000_0ff7;0x008000 - 0xffffff -dq 0x00c0_9200_8000_0ff7 - -dap: -dw 0x0010 -.length dw 0x0001 -.offset dw 0x7e00 -.segment dw 0x0000 -.start dq 0x0000_0000_0000_0001 - -memory_usage: -.low dw ;word - used memory from 0 to 1MiB in kiB -.mid dw 0x0000;word - used memory from 1MiB to 16MiB in kiB -.high dw 0x0000;word - used memory from 16MiB up in 64s of kiB
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