still need to read, parse root directory to find kernel and need to put boot signature at 0x7dfe to jump around

doc/design/kernel_functions.txt

@@ -0,0 +1,4 @@
+allocate:
+  ax in: number of pages
+  dx in: process id
+  ebx out: address, or 0x0000_0000 on failure

doc/design/memory_map.txt

@@ -0,0 +1,16 @@
+0x0000 - 0x03ff : interrupt vector table
+0x0400 - 0x04ff : bios data area
+0x0500 - 0x05ff : structure pointers
+  0x00 dword : fat pointer
+0x0600 - 0x1fff : not assigned
+0x2000 - 0x3fff : memory map
+  for each word : 1 page
+    0x0000 = free
+    0x0001 = unavailable
+    0x0002 = kernel
+    other = process number
+
+0x4000 - 0x6fff : not assigned
+0x7000 - 0x7bff : bootloader scratch
+  0x7000 : memory map bios buffer
+0x7c00 - 0x7fff : bootloader

makefile

@@ -0,0 +1,12 @@
+floppy: out bootloader
+	mkfs.fat -C -f 1 -F 12 -n "PORTLAND OS" -R 2 -S 512 out/floppy.img 1440
+	dd if=obj/bootloader.bin of=out/floppy.img bs=1 seek=62 conv=notrunc
+
+bootloader: obj
+	nasm src/bootloader.bin -o obj/bootloader.bin
+
+obj:
+	mkdir -p obj
+
+out:
+	mkdir -p out

src/bootloader.asm

@@ -0,0 +1,246 @@
+;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.
+
+pointers:
+.fat equ 0x0500
+
+fat_header:
+.oem_name            equ 0x7c03;mkfs.fat    - ignored
+.bytes_per_sector    equ 0x7c0b;0x0200      - assumed
+.sectors_per_cluster equ 0x7c0d;0x01        - assumed
+.reserved_sectors    equ 0x7c0e;0x0002      - other values handled
+.n_fats              equ 0x7c10;0x01        - assumed
+.directory_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 - assumed
+.long_sectors        equ 0x7c20;0x0000_0000 - assumed
+.drive_number        equ 0x7c24;            - ignored, used as scratch
+.flags               equ 0x7c25;            - ignored
+.signature           equ 0x7c26;0x29        - halts on other values
+.id                  equ 0x7c27;            - ignored
+.label               equ 0x7c2b;PORTLAND OS - assumed
+.fs_type             equ 0x7c36;FAT12       - assumed
+
+org 0x7c3e
+bits 16
+
+  in al, 0x92
+  or al, 0x02
+  out 0x92, al
+
+  mov ah, 0x42
+  mov si, dap
+  int 0x13
+
+  mov byte [fat_header.drive_number], dl
+
+memory:
+  mov bx, 0x2010
+  mov eax, 0x0001_0001
+.clear:
+  mov dword [bx], eax
+  add bx, 4
+  test bx, 0x4000
+  jne .clear
+
+  xor ax, ax
+  mov es, ax
+  mov si, 0x7000
+  xor ebx, ebx
+
+.loop:
+  mov eax, 0x0000_e820
+  mov ecx, 24
+  mov edx, 0x534d_4150
+  int 0x15
+  jc .done
+
+  test cl, 24
+  jne .not_24
+
+  test byte [0x7014], 0x01
+  jz .loop
+
+.not_24:
+  test dword [0x7010], 1
+  jne .loop
+
+  test byte [0x7003], 0
+  jne .loop
+
+  test dword [0x7004], 0
+  jne .loop
+
+  test dword [0x700c], 0
+  je .check_lower
+
+  mov dword [0x7008], 0xffff_ffff
+
+.check_lower:
+  test dword [0x7008], 0
+  je .loop
+
+  mov edx, ebx
+  mov ebx, dword [0x7000]
+  mov eax, ebx
+  add eax, dword [0x7008]
+  jnc .pagify
+  mov eax, 0xffff_ffff
+
+.pagify:
+  dec ebx
+  shr ebx, 12
+  inc ebx
+  shr eax, 12
+  dec eax
+
+  test eax, 0xffff_f000
+  jz .maxed
+  mov eax, 0x0000_0fff
+
+.maxed:
+  inc eax
+  test eax, ebx
+  je .next
+
+  shl ebx, 1
+  or ebx, 0x2000
+  shl eax, 1
+  add eax, 0x2000
+  mov ecx, eax
+
+  xor ax, ax
+.free_loop:
+  mov word [ebx], ax
+  add ebx, 2
+  test ebx, ecx
+  jne .free_loop
+
+.next:
+  mov ebx, edx
+  jmp .loop
+
+.done:
+  mov dword [0x2000], 0x0002_0002
+  mov dword [0x2004], 0x0002_0002
+  mov dword [0x2008], 0x0002_0002
+  mov dword [0x200c], 0x0002_0002
+
+  test byte [fat_header.signature], 0x29
+  jne halt
+
+  mov ax, word [fat_header.sectors_per_fat]
+  mov word [dap.length], ax
+
+  dec ax
+  shr ax, 3
+  inc ax
+
+fat_allocate:
+  mov bx, 0x200e
+  xor cx, cx
+  mov dx, 0x2200
+
+.loop:
+  add bx, 2
+  test bx, dx
+  je halt
+
+  test word [bx], 0x0000
+  je .eq
+
+  xor cx, cx
+  jmp .loop
+
+.eq:
+  inc cx
+  test cx, ax
+  jne .loop
+
+  dec ax
+  shl ax, 1
+  sub bx, ax
+  mov dx, bx
+
+  mov ax, 0x0002
+.mark_loop:
+  mov word [bx], ax
+  loop .mark_loop
+
+  mov bx, dx
+  and ebx, 0x0000_dfff
+  shl ebx, 12
+
+  mov dword [pointers.fat], ebx
+
+  mov dl, byte [fat_header.drive_number]
+  mov ax, word [fat_header.reserved_sectors]
+  mov word [dap.start], ax
+  mov word [dap.offset], bx
+  shr ebx, 16
+  and bx, 0xf000
+  mov word [dap.segment], bx
+
+  mov ah, 0x42
+  mov si, dap
+  int 0x15
+
+  mov ebx, dword [pointers.fat]
+
+  ;fat loaded - load kernel
+
+  cli
+
+  lgdt [gdt]
+  mov eax, cr0
+  or al, 0x01
+  mov cr0, eax
+  jmp 0x08:pmode
+
+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 1
+
+allocate:
+  ;TODO
+  ret
+
+halt:
+  cli
+.hlt:
+  hlt
+  jmp .hlt
+
+bits 32
+pmode:
+