SLRboot/slrboot.nasm

ORG 0x7C00
BITS 16
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; SLRboot
; Bootloader for SingOS
; version 0.2.0.3-exp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
cli
jmp long 0x0000:start

start:
mov ax, 0x1000
mov ss, ax
mov sp, 0xb000
mov ax, 0
mov ds, ax
mov es, ax
mov [disk_identifier], dl
sti
mov si, 0x7c00
mov di, 0x600
mov cx, 0x100
rep movsw
mov bx, relocated
sub bx, 0x7600 ; Calculate the offset.
push bx
ret ; Return far
;jmp long 0:bx

relocated:

mov si, message ; Put address of the null-terminated string to output into 'si'
call print      ; Call our string-printing routine

; Check for more than one active partition that we can start from. 
xor bx, bx
xor cx, cx
mov ax, [partition_1.active_partition]
cmp ax, 0x80
jne check_p_2
mov bx, 0x01 ; Partion 1 active
inc cx

check_p_2:
mov ax, [partition_2.active_partition]
cmp ax, 0x80
jne check_p_3
inc cx
mov bx, 0x02 ; Partion 2 active

check_p_3:
mov ax, [partition_3.active_partition]
cmp ax, 0x80
jne check_p_4
inc cx
mov bx, 0x03 ; Partion 3 active

check_p_4:
mov ax, [partition_4.active_partition]
cmp ax, 0x80
jne eval_active_partion_number
inc cx
mov bx, 0x04 ; Partion 4 active

eval_active_partion_number: 
cmp cx, 1
je boot_partition
; here goes wait call, for the user to enter debug mode. 
; Wating for 2 seconds: 
mov ah, 0x86   ; code for waiting interupt call
mov cx, 0x001e ; high count of microseconds
mov dx, 0x8480 ; low count
int 0x15
.busy_wait_for_key:
xor ax, ax 
mov ah, 0x01 ; BIOS call to wait for key
int 0x16


boot_partition:
; IMPORTANT bx, has to hold the value 1-4 for the partiotion that wanted to be booted.  

mov bx, 2

mov ax, partition_1
.loop:
    cmp bx, 1 
    je break
    add ax, 0x10
    ;call dumpax
    dec bx
    jmp .loop
break:

add ax, 8 ; This is the offset to fetch the LBA start adress of the partition record
mov bx, ax
xor ax, ax
mov ax, [bx] ; first part of LBA
mov WORD [DAPACK.lba_addr_dw_low], ax
call dumpax
add bx, 2 ; next part
mov ax, [bx]
mov WORD [DAPACK.lba_addr_dw_low + 1], ax
call dumpax
cli 
hlt
mov WORD [DAPACK.blkcnt],          0x01  
mov WORD [DAPACK.db_addr_segment], 0x0000
mov WORD [DAPACK.db_addr_offset],  0x7c00
mov si, DAPACK  ; address of "disk address packet"
xor ax, ax                          
mov ah, 0x42                            ; READ
mov dl, [disk_identifier] 
int 0x13

jmp long 0x0:0x7c00

cli 
hlt


%IF 0
cli
jmp long 0x0000:start

start:
xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax
mov [disk_identifier], dl

; initialize stack
; Set up 4K stack after this bootloader
; [Remember: Effective Address = Segment*16 + Offset]
mov ax, 0x7C0   ; Set 'ax' equal to the location of this bootloader divided by 16
add ax, 0x20     ; Skip over the size of the bootloader divided by 16
mov ss, ax      ; Set 'ss' to this location (the beginning of our stack region)
mov sp, 8192    ; Set 'ss:sp' to the top of our 8K stack
sti
mov si, message ; Put address of the null-terminated string to output into 'si'
call print      ; Call our string-printing routine

mov si, enter_debug_mode
call print 
call printCRLF
;%IF 0
; here goes wait call, for the user to enter debug mode. 
; Wating for 2 seconds: 
mov ah, 0x86   ; code for waiting interupt call
mov cx, 0x001e ; high count of microseconds
mov dx, 0x8480 ; low count
int 0x15

.busy_wait_for_key:
xor ax, ax 
mov ah, 0x01 ; BIOS call to wait for key
int 0x16
jnz debug_mode

; entering system check: 
mov si,  enter_system_check

mov si, sys_check_ok ; Put address of the null-terminated string to output into 'si'
call print      ; Call our string-printing routine

mov si, boot_system ; Put address of the null-terminated string to output into 'si'
call print      ; Call our string-printing routine

;This goes first as to now overwrite %ah and %al.
;mov ax, 0x0050 
;mov es, ax                  ;Section to write into
;mov ah, 0x2                 ;Read sectors from drive
;mov al, 0x08                ;Number of sectors to read (31 * 512 = 15872 bytes)
;mov ch, 0x0                 ;Low 8 bits of cylinder
;mov cl, 0x11                ;First sector to read (bits 0-5), upper bits of cylinder (bits 6-7)
;mov dh, 0x0                 ;Head number
;mov dl, [disk_identifier]   ;Drive number
;mov bx, 0x0000               ;Offset into section
;int 0x13                    ;Low level disk services

;jnc notcarry
;mov si, error_str
;call print
;jmp endcarrycheck

notcarry:
;mov si, success_str
;call print
;call printCRLF

mov ax, 0x0
mov ds, ax
mov ax, 89 ; lba adress

jmp 0x50:0x0000   ; Jump to the kernel 

endcarrycheck:  
cli             ; Clear the Interrupt Flag (disable external interrupts)
hlt             ; Halt the CPU (until the next external interrupt)

debug_mode: 
mov si, .welcome_debug
call print 
cli             ; Clear the Interrupt Flag (disable external interrupts)
hlt 

.welcome_debug db 'This is debug mode', 0

printCRLF:
mov ah, 0xE
mov al, 13
int 0x10
mov al, 10
int 0x10
ret
%ENDIF

;Routine for printing a 'ax' as hex
dumpax:
pusha           ; save registers
mov bx, ax
mov ah, 0xE     ; Teletype output

mov cx, 4       ; 4 nipples in a 16 bit word
.loop:
rol bx, 4       ; rotate to next nipple
mov al, bl      ; we copy to al because we need to mask only the low 4 bits
and al, 1111b   ; Do the masking
add al, '0'     ; convert to ASCII
cmp al, '9'     ; If we are greater than 9 ascii, we add 7 to make digit 10 be represented as 'A'
jbe .skip       ;  -|-
add al, 7       ;  -|-
.skip:          ;  -|-
int 0x10        ; BIOS call 'output'
loop .loop

popa            ; restore registers
ret

; Routine for outputting string in 'si' register to screen
print:
mov ah, 0xE     ; Specify 'int 0x10' 'teletype output' function
                ; [AL = Character, BH = Page Number, BL = Colour (in graphics mode)]
.printchar:
lodsb           ; Load byte at address SI into AL, and increment SI
cmp al, 0
je .done        ; If the character is zero (NUL), stop writing the string
int 0x10         ; Otherwise, print the character via 'int 0x10'
jmp .printchar  ; Repeat for the next character
.done:
ret

data:
message db 'SLRboot for SingOS! v0.2.0.3-exp',13,10,0
;enter_debug_mode db 'Press d to enter bootloader debug mode',13,10,0
;enter_system_check db 'Performing system check:',13,10,0
;sys_check_ok db 'System check ok', 13, 10, 0
;boot_system db 'Read SingOS from disk', 13, 10, 0
;error_str db 'Error', 0
;success_str db 'Success', 0
boot_this_partition: dw 0
disk_identifier db 0


DAPACK:
  .dap_Size:         db  0x10   ; This is always 16 bytes (0x10)
  .rev_byte:         db  0x0    ; reserved byte, should always be zero
  .blkcnt:           dw  0x0    ; int 13 resets this to # of blocks actually read/written
  .db_addr_offset:   dw  0x0    ; memory buffer destination address (0:7c00)
  .db_addr_segment:  dw  0x0    ; in memory page zero
  .lba_addr_dw_low:  dd  0x0    ; put the lba to read in this spot
  .lba_addr_dw_high: dd  0x0    ; more storage bytes only for big lba's ( > 4 bytes ) 


; Pad to 510 bytes (boot sector size minus 2) with 0s, and finish with the two-byte standard boot signature
times 446-($-$$) db 0 ; First partion entry
partition_1:
.active_partition db 0x80 
.start_CHS db 0x00, 0x00, 0x11;0x20, 0x21, 0x00 
.disk_type db 0x83 
.end_CHS db 0x8C, 0x3D, 0x0F 
.start_LBA db 0x10, 0x00, 0x00, 0x00 
.size db 0x00, 0xC8, 0x03, 0x00  

partition_2:
.active_partition db 0x80 
.start_CHS db 0x8C, 0x3E, 0x0F 
.disk_type db 0x83 
.end_CHS db 0xFF, 0xFF, 0xFF 
.start_LBA db 0x00, 0xD0, 0x03, 0x00 
.size db 0x00, 0x28, 0x1C, 0x03 

partition_3:
.active_partition db 0x00 
.start_CHS db 0x00, 0x00, 0x00 
.disk_type db 0x00 
.end_CHS db 0x00, 0x00, 0x00 
.start_LBA db 0x00, 0x00, 0x00, 0x00 
.size db 0x00, 0x00, 0x00, 0x00 

partition_4:
.active_partition db 0x00 
.start_CHS db 0x00, 0x00, 0x00 
.disk_type db 0x00 
.end_CHS db 0x00, 0x00, 0x00 
.start_LBA db 0x00, 0x00, 0x00, 0x00 
.size db 0x00, 0x00, 0x00, 0x00

times 510-($-$$) db 0
dw 0xAA55           ; => 0x55 0xAA (little endian byte order)
; bootloder debug_mode goes here

times 8192-($-$$) db 0



; mov si, 0x7be
; cmp byte [si], al
; jne 0x33
; add si, 0x10
; cmp si, 0x7fe
; jne 0x24
; jmp 0x49
; mov ah, 2
; mov al, 1
; mov bx, 0x7c00
; mov dl, 0x80
; mov dh, byte [si + 1]
; mov cx, word [si + 2]
; int 0x13
; jmp long 0:0x7c00

; jmp 0x49