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tools for building iso #29

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227 changes: 227 additions & 0 deletions tools/boot_dvd.asm
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; boot_dvd.asm - NASM translation of TempleOS BootDVD.HC
; Boot loader for CD/DVD-ROM booting via El Torito
; Assembled with: nasm -f bin -o boot_dvd.bin boot_dvd.asm

BITS 16

; Constants from KernelA.HH
%define BLK_SIZE_BITS 9
%define BLK_SIZE (1 << BLK_SIZE_BITS) ; 512
%define DVD_BLK_SIZE (4 * BLK_SIZE) ; 2048
%define DVD_BOOT_LOADER_SIZE DVD_BLK_SIZE ; 2048
%define BOOT_RAM_BASE 0x07C00
%define BOOT_RAM_LIMIT 0x97000
%define BOOT_STK_SIZE BLK_SIZE ; 512
%define BOOT_SRC_DVD 4

; BOOT_HIGH_LOC = (BOOT_RAM_LIMIT - (BOOT_STK_SIZE + DVD_BOOT_LOADER_SIZE)) >> 4
; = (0x97000 - (512 + 2048)) >> 4 = (0x97000 - 0xA00) >> 4 = 0x96600 >> 4 = 0x9660
%define BOOT_HIGH_LOC 0x9660

BDVD_START:
cld
mov ax, BOOT_HIGH_LOC
mov es, ax

cli
mov ss, ax
mov sp, BOOT_STK_SIZE + DVD_BOOT_LOADER_SIZE
sti

; Determine our load address and copy ourselves to BOOT_HIGH_LOC
call BDVD_GET_RIP
BDVD_GET_RIP:
pop bx
sub bx, BDVD_GET_RIP - BDVD_START
shr bx, 4
mov ax, cs
add ax, bx
mov ds, ax
mov cx, DVD_BOOT_LOADER_SIZE
xor si, si
xor di, di
rep movsb

mov ax, BOOT_HIGH_LOC
mov ds, ax

; Far jump to relocated code at BOOT_HIGH_LOC:BDVD_MAIN
db 0xEA
dw BDVD_MAIN - BDVD_START, BOOT_HIGH_LOC

; Data area
BDVD_BIOS_DRV_NUM: db 0
BDVD_PAGE: db 0

; BIOS Disk Address Packet for INT 13h/AH=42h
BDVD_DAP: db 16, 0 ; size=16, reserved=0
db 1, 0 ; count=1, reserved=0
BDVD_DAP_BUF: dw 0, 0 ; offset, segment
BDVD_DAP_BLK: dq 0 ; LBA

BDVD_TEMPLEOS_MSG: db "Loading TempleOS", 0
BDVD_NOT64_MSG: db "TempleOS requires a 64-bit capable processor.", 13, 10, 0

; These fields get patched by build_iso.py with the kernel location
; Offsets from BDVD_START are used for patching
BDVD_BLK_LO: dw 0 ; DVD LBA low word
BDVD_BLK_HI: dw 0 ; DVD LBA high word
BDVD_BLK_CNT: dw 0 ; Number of DVD blocks to read
BDVD_SHIFT_BLKS: dw 0 ; Sub-block alignment offset
BDVD_PROGRESS_STEP: dd 0
BDVD_PROGRESS_VAL: dd 0

; Put a character to screen via BIOS
BDVD_PUT_CHAR:
mov ah, 0x0E
mov bl, 7
mov bh, [BDVD_PAGE - BDVD_START]
int 0x10
BDVD_RET:
ret

; Print null-terminated string at DS:SI
BDVD_PUTS:
.loop:
lodsb
test al, al
jz BDVD_RET
call BDVD_PUT_CHAR
jmp .loop

; Main entry point (runs after relocation)
BDVD_MAIN:
mov [BDVD_BIOS_DRV_NUM - BDVD_START], dl

; Get current video page
mov ah, 0x0F
int 0x10
mov [BDVD_PAGE - BDVD_START], bh

; Check for 64-bit CPU support
mov eax, 0x80000000
cpuid
cmp eax, 0x80000001
jb .not64

mov eax, 0x80000001
cpuid
bt edx, 29
jc .is64

.not64:
mov si, BDVD_NOT64_MSG - BDVD_START
call BDVD_PUTS
.hang:
jmp .hang

.is64:
mov si, BDVD_TEMPLEOS_MSG - BDVD_START
call BDVD_PUTS

; Set up ES to point to kernel load area
mov ax, BOOT_RAM_BASE / 16
mov es, ax
xor ecx, ecx
mov cx, [BDVD_BLK_CNT - BDVD_START]

; Calculate progress bar step
mov eax, (80 - 7 - 9) * 65536 ; 64 columns * 65536
xor edx, edx
div ecx
mov [BDVD_PROGRESS_STEP - BDVD_START], eax
mov dword [BDVD_PROGRESS_VAL - BDVD_START], 0

; Load starting LBA
mov ax, [BDVD_BLK_LO - BDVD_START]
mov dx, [BDVD_BLK_HI - BDVD_START]

; Read kernel blocks from CD/DVD
.read_loop:
push cx ; save block count
push ax ; save LBA low
push dx ; save LBA high
push es ; save buffer segment

; Set up DAP for INT 13h
mov [BDVD_DAP_BLK - BDVD_START], ax
mov [BDVD_DAP_BLK + 2 - BDVD_START], dx
mov ax, es
mov [BDVD_DAP_BUF + 2 - BDVD_START], ax ; segment
mov si, BDVD_DAP - BDVD_START ; DS:SI = DAP
mov ah, 0x42
mov dl, [BDVD_BIOS_DRV_NUM - BDVD_START]
int 0x13

; Advance buffer by one DVD block
pop ax ; ES
add ax, DVD_BLK_SIZE / 16
mov es, ax
pop dx ; LBA high
pop ax ; LBA low
inc ax
jnz .no_carry
inc dx
.no_carry:

; Print progress dot
push ax
mov bx, [BDVD_PROGRESS_VAL + 2 - BDVD_START]
mov eax, [BDVD_PROGRESS_STEP - BDVD_START]
add [BDVD_PROGRESS_VAL - BDVD_START], eax
cmp [BDVD_PROGRESS_VAL + 2 - BDVD_START], bx
je .no_dot
mov al, '.'
call BDVD_PUT_CHAR
.no_dot:
pop ax

pop cx
loop .read_loop

; Shift data backward to align on 512-byte boundary within DVD block
push ds
mov bx, [BDVD_SHIFT_BLKS - BDVD_START]
shl bx, BLK_SIZE_BITS - 4 ; Convert blocks to segment offset
mov cx, [BDVD_BLK_CNT - BDVD_START]
mov ax, BOOT_RAM_BASE / 16
mov es, ax
add ax, bx
mov ds, ax
.shift_loop:
push cx
xor si, si
xor di, di
mov cx, DVD_BLK_SIZE / 4
rep movsd
mov ax, ds
add ax, DVD_BLK_SIZE / 16
mov ds, ax
mov ax, es
add ax, DVD_BLK_SIZE / 16
mov es, ax
pop cx
loop .shift_loop
pop ds

; Pass boot info to kernel in registers
; EBX = 32-bit LBA (BLK_LO in low word, BLK_HI in high word)
mov ebx, dword [BDVD_BLK_LO - BDVD_START]
; EAX = SHIFT_BLKS in high word, BOOT_SRC_DVD in low word
mov ax, [BDVD_SHIFT_BLKS - BDVD_START]
shl eax, 16
mov ax, BOOT_SRC_DVD

; Far jump to kernel entry point at BOOT_RAM_BASE
db 0xEA
dw 0x0000, BOOT_RAM_BASE / 16

BDVD_END:

; Verify boot loader fits in DVD_BOOT_LOADER_SIZE
%if (BDVD_END - BDVD_START) > DVD_BOOT_LOADER_SIZE
%error "Boot loader exceeds DVD_BOOT_LOADER_SIZE"
%endif

; Pad to exactly DVD_BOOT_LOADER_SIZE
times DVD_BOOT_LOADER_SIZE - (BDVD_END - BDVD_START) db 0
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