first commit
This commit is contained in:
Elaina Claus
219
src/vbr/vbr.s
Executable file
219
src/vbr/vbr.s
Executable file
@@ -0,0 +1,219 @@
|
||||
; Copyright (C) 2020 Bradley Claus
|
||||
;
|
||||
; This program is free software: you can redistribute it and/or modify
|
||||
; it under the terms of the GNU General Public License as published by
|
||||
; the Free Software Foundation, either version 3 of the License, or
|
||||
; (at your option) any later version.
|
||||
;
|
||||
; This program is distributed in the hope that it will be useful,
|
||||
; but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
; GNU General Public License for more details.
|
||||
;
|
||||
; You should have received a copy of the GNU General Public License
|
||||
; along with this program. If not, see <https://www.gnu.org/licenses/>.
|
||||
|
||||
[BITS 16]
|
||||
[ORG 0x7C00]
|
||||
[CPU KATMAI]
|
||||
jmp short init
|
||||
nop
|
||||
|
||||
bpb_start:
|
||||
; fill BPB area with 0x00 since we skip writing this part to disk
|
||||
; but we need it for the 'jmp short entry; nop' above
|
||||
times 33 db 0x00
|
||||
|
||||
ebpb_start:
|
||||
; fill BPB area with 0x00 since we skip writing this part to disk
|
||||
; but we need it for the 'jmp short entry; nop' above
|
||||
times 54 db 0x00
|
||||
|
||||
%include "entry.inc"
|
||||
init:
|
||||
cli ; We do not want to be interrupted
|
||||
|
||||
xor ax, ax ; 0 AX
|
||||
mov ds, ax ; Set segment registers to 0
|
||||
mov es, ax ; *
|
||||
|
||||
mov ss, ax ; Set Stack Segment to 0
|
||||
mov sp, STACK_START ; Setup stack
|
||||
mov bp, sp ; base ptr = stack ptr
|
||||
|
||||
mov bx, VBR_ENTRY ; move BP to the new start of the initial boot sector
|
||||
|
||||
jmp 0:main ; fix up cs:ip just in case and jump to relocated code
|
||||
|
||||
%include "config.inc"
|
||||
%include "errors.inc"
|
||||
%include "memory.inc"
|
||||
|
||||
%include "partition_table.inc"
|
||||
|
||||
%include "fat32/bpb.inc"
|
||||
|
||||
|
||||
|
||||
main:
|
||||
sti ; all done with inital setup and relocation, reenable interupts
|
||||
mov [bsDriveNumber], dl ; BIOS passes drive number in DL
|
||||
mov [partition_offset], si ; save passed partition entry offset
|
||||
|
||||
.check_FAT_size:
|
||||
cmp dword [bsSectorHuge], 0 ; SectorsHuge will not be set if FAT12/16
|
||||
ja main.load_stage2
|
||||
|
||||
ERROR VBR_ERROR_WRONG_FAT_SIZE
|
||||
|
||||
; read sectors 1-63 to stage2 entry point
|
||||
.load_stage2:
|
||||
push bp
|
||||
mov bp, sp
|
||||
|
||||
;uint8_t read_disk_raw(size_t count, uint16_t buf_segment, uint16_t buf_offset,
|
||||
; uint16_t lower_lower_lba, uint16_t upper_lower_lba)
|
||||
|
||||
xor ax, ax
|
||||
push ax ; upper_lower_lba = 0
|
||||
|
||||
mov ax , 1
|
||||
push ax ; lower_lower_lba = 1
|
||||
|
||||
xor ax, ax
|
||||
push ax ; offset = 0
|
||||
|
||||
; 07E0:0
|
||||
mov ax, STAGE2_ENTRY
|
||||
shr ax, 4
|
||||
push ax ; segment = 7E0
|
||||
|
||||
mov ax, STAGE2_SECTOR_COUNT
|
||||
push ax
|
||||
|
||||
call read_disk_raw
|
||||
leave
|
||||
|
||||
.check_sig:
|
||||
mov ax, 0x7E0
|
||||
mov fs, ax
|
||||
cmp dword [fs:0x7FFC], 0xDEADBEEF
|
||||
je main.sig_ok
|
||||
|
||||
ERROR VBR_ERROR_NO_SIGNATURE ; no signature present in stage2
|
||||
|
||||
.sig_ok:
|
||||
push bp
|
||||
mov bp, sp
|
||||
mov ax, fat32_bpb_SIZE ; size in byte
|
||||
push ax
|
||||
mov ax, bpb_start ; start of bpb
|
||||
push ax
|
||||
mov ax, fat32_bpb ; defined in memory.inc, destination
|
||||
push ax
|
||||
call kmemcpy ; copy bpb to memory
|
||||
leave
|
||||
|
||||
push bp
|
||||
mov bp, sp
|
||||
mov ax, fat32_ebpb_SIZE ; 72 bytes of data
|
||||
push ax
|
||||
mov ax, ebpb_start ; start of ebpb
|
||||
push ax
|
||||
mov ax, fat32_ebpb ; defined in memory.inc, destination
|
||||
push ax
|
||||
call kmemcpy ; copy ebpb to memory
|
||||
leave
|
||||
|
||||
mov si, [partition_offset]
|
||||
mov dl, [bsDriveNumber]
|
||||
jmp 0:0x7E00
|
||||
|
||||
stop:
|
||||
hlt
|
||||
jmp short stop
|
||||
|
||||
; Wrapper for AH=0x42 INT13h (Extended Read)
|
||||
;
|
||||
; BIOS call details
|
||||
; AH = 42h
|
||||
; DL = drive number
|
||||
; DS:SI -> disk address packet
|
||||
;
|
||||
; Return:
|
||||
; CF clear if successful
|
||||
; AH = 00h
|
||||
; CF set on error
|
||||
; AH = error code
|
||||
; disk address packet's block count field set to number of blocks
|
||||
; successfully transferred
|
||||
;
|
||||
;
|
||||
; uint8_t read_disk_raw(uint16_t buf_segment, uint16_t buf_offset, uint16_t lower_lower_lba, uint16_t upper_lower_lba)
|
||||
; bp-0 = call frame
|
||||
; bp-2 = upper_lower_lba
|
||||
; bp-4 = lower_lower_lba
|
||||
; bp-6 = offset
|
||||
; bp-8 = segment
|
||||
; bp-10 = count
|
||||
; bp-12 = ret ptr
|
||||
read_disk_raw:
|
||||
push si
|
||||
|
||||
; uint8_t* kmemset(void* dest, uint8_t val, size_t len);
|
||||
push bp
|
||||
mov bp, sp
|
||||
|
||||
mov ax, 0x10
|
||||
push ax ; len = 16 bytes
|
||||
xor ax, ax
|
||||
push ax ; val = 0
|
||||
mov ax, lba_packet
|
||||
push ax ; dest = lba_packet address
|
||||
|
||||
call kmemset
|
||||
leave
|
||||
|
||||
mov byte [lba_packet + LBAPkt_t.size], 0x10
|
||||
mov word [lba_packet + LBAPkt_t.xfer_size], STAGE2_SECTOR_COUNT
|
||||
|
||||
mov ax, [bp-2]
|
||||
shl eax, 16
|
||||
mov ax, [bp-4]
|
||||
mov dword [lba_packet + LBAPkt_t.lower_lba], eax
|
||||
|
||||
mov ax, [bp-6]
|
||||
mov word [lba_packet + LBAPkt_t.offset], ax
|
||||
|
||||
mov ax, [bp-8]
|
||||
mov word [lba_packet + LBAPkt_t.segment], ax
|
||||
|
||||
mov si, lba_packet
|
||||
mov ah, 0x42
|
||||
mov dl, byte [bsDriveNumber]
|
||||
int 0x13
|
||||
jnc read_disk_raw.endf
|
||||
|
||||
ERROR VBR_ERROR_DISK_READ_ERR
|
||||
.endf:
|
||||
pop si
|
||||
ret
|
||||
; Data
|
||||
|
||||
; #############
|
||||
;
|
||||
; Locals
|
||||
;
|
||||
; #############
|
||||
|
||||
; offset from the begining of sector 0 to the active partition.
|
||||
partition_offset:
|
||||
dw 0x0000
|
||||
|
||||
%assign bytes_remaining (420 - ($ - $$))
|
||||
%warning VBR has bytes_remaining bytes remaining for code (MAX: 420 bytes)
|
||||
|
||||
times (510 - ($ - $$)) nop ; Fill the rest of sector with nop
|
||||
|
||||
BootSig:
|
||||
dw 0xAA55 ; Add boot signature at the end of bootloader
|
||||
Reference in New Issue
Block a user