small changes, part 2, rewriting bootloader partially, giving up on this branch

1 files changed, 187 insertions, 277 deletions

diff --git a/src/bootloader.asm b/src/bootloader.asm
index 583c169..f18750c 100644
--- a/src/bootloader.asm
+++ b/src/bootloader.asm
@@ -15,275 +15,245 @@
 ;TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE
 ;USE OR PERFORMANCE OF THIS SOFTWARE.
 
-pointers:
-.fat equ 0x0500
-.root_dir equ 0x0504
-.kernel equ 0x0508
-
-fat_header:
-.oem_name            equ 0x7c03;mkfs.fat    - ignored
-.bytes_per_sector    equ 0x7c0b;0x0200      - assumed
-.sectors_per_cluster equ 0x7c0d;0x01        - assumed
+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        - assumed
+.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 - assumed, top half used as scratch for sector number of cluster 0
-.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
+.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:
-  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
+  ;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
-  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
-
+  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]
-  xor ecx, ecx
-  mov cx, word [fat_header.reserved_sectors]
-
-  call allocate_and_load
-
-  mov dword [pointers.fat], ebx
+  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]
-  dec ax
   shr ax, 4
-  inc ax
+  call load_low
+  mov dword [global_info.root_dir], ebx
 
+  ;Calculate end of root directory
   xor ecx, ecx
-  mov cx, word [fat_header.reserved_sectors]
-  add cx, word [fat_header.sectors_per_fat]
-  jnc .no_carry
-  or ecx, 0x0001_0000
-.no_carry:
-
-  call allocate_and_load
-
-  mov dword [pointers.root_dir], ebx
-
-  xor edx, edx
-  mov dx, word [fat_header.root_dir_entries]
-  shl edx, 5
-  add edx, ebx
+  mov cx, word [fat_header.root_dir_entries]
+  shl ecx, 5
+  add ecx, ebx
+  jc insufficient_memory
 
 find_kernel:
-  mov eax, 0x6e_72_65_6b;kern
-  mov ecx, 0x20_20_6c_65;el
-  mov ebx, dword [pointers.root_dir]
-
+  mov eax, 0x6e72_656b;kern
+  mov edx, 0x2020_6c65;el
 .loop:
+  ;Check name
   test dword [ebx], eax
   jne .next
-  test dword [ebx + 4], ecx
+  test dword [ebx + 4], edx
   jne .next
-  test word [ebx + 8], 0x79_73;sy
+  test word [ebx + 8], 0x7973;sy
   jne .next
   test byte [ebx + 10], 0x73;s
   je .found
-
 .next:
+  ;Next record
   add ebx, 32
-  test ebx, edx
+  test ebx, ecx
   jne .loop
-  jmp halt
 
+  ;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:
-  mov byte [allocate_and_load.load], 0xc3;ret
+  ;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
 
-  mov eax, dword [ebx + 0x1c]
-  dec eax
-  shr eax, 9
-  inc eax
+load_kernel:
+  
 
-  test eax, 0xffff_0000
-  jnz halt
+load_low:
+  ;ax in : number of sectors
+  ;qword [dap.start] in : starting sector
 
-  push word [ebx + 0x1a]
+  ;Store length in DAP
+  mov word [dap.length], ax
 
-  call allocate_and_load
+  ;Calculate kiB used
+  dec ax
+  shr ax, 1
+  inc ax
+  mov dx, ax
+  add ax, word [global_info.mem_usage]
 
-  mov dword [pointers.kernel], ebx
+  ;Fail if not enough is available
+  jc insufficient_memory
+  cmp ax, word [global_info.low_mem]
+  jg insufficient_memory
 
-  mov ax, word [fat_header.root_dir_entries]
-  dec ax
-  shr ax, 4
-  dec ax
-  add ax, word [fat_header.reserved_sectors]
-  jc halt
-  add ax, word [fat_header.sectors_per_fat]
-  jc halt
-  mov word [fat_header.hidden_sectors + 2], ax
+  ;Check if address will fit in DAP
+  test ah, ah
+  jnz insufficient_memory
 
-load_kernel:
-  mov word [dap.length], 0x0001
-  mov word [dap.offset], bx
-  xor bx, bx
-  shr ebx, 4
-  jmp .over_sig
-
-times $$ + 0x01fe - $ db 0
-dw 0xaa55
-
-.over_sig:
-  test ebx, 0xffff_0000
-  jnz halt
+  ;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:
 
-  xor edx, edx
-  pop dx
-  mov word [dap.start + 2], 0x0000
-  mov ah, 0x42
+  ;Load from disk
   mov si, dap
-.loop:
-  mov cx, dx
-  add cx, word [fat_header.hidden_sectors + 2]
-  jc halt
-
-  mov word [dap.start], cx
-
+  mov ah, 0x42
   int 0x13
+  shl ebx, 4
+  ret
 
-  mov ebx, dword [pointers.fat]
-  add ebx, edx
-  add ebx, edx
-  add ebx, edx
-
-  xor edx, edx
-  mov dx, word [ebx + 1]
-  shl edx, 8
-  mov dl, byte [ebx]
-
-  add word [dap.segment], 0x0020
-  jc halt
-
-  mov ecx, edx
-  and ecx, 0x0ff8
-  test ecx, 0x0ff8
-  jne .loop
-
-  mov ebx, dword [pointers.kernel]
-
-  ;TODO
+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
-
-  lgdt [gdt]
-  mov eax, cr0
-  or al, 0x01
-  mov cr0, eax
-  jmp 0x08:kernel_start;get start from file header
+.halt:
+  hlt
+  jmp .halt
 
 gdt:
 dw 0x28
@@ -299,69 +269,9 @@ dw 0x0010
 .length  dw 0x0001
 .offset  dw 0x7e00
 .segment dw 0x0000
-.start   dd 0x0000_0001
-.start_h dd 0x0000_0000
-
-;ecx = sector
-;ax = sector count
-;bx out = address of start
-allocate_and_load:
-  mov word [dap.length], ax
-  mov dword [dap.start], ecx
-
-  dec ax
-  shr ax, 3
-  inc ax
+.start   dq 0x0000_0000_0000_0001
 
-  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
-
-.load:
-  mov eax, ebx
-  mov word [dap.offset], ax
-  shr eax, 4
-  and ax, 0xf000
-  mov word [dap.segment], ax
-
-  mov ah, 0x42
-  mov si, dap
-  int 0x13
-
-  ret
-
-halt:
-  cli
-.hlt:
-  hlt
-  jmp .hlt
+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
\ No newline at end of file