nivirx/stevia
1
0
Fork 0
Code Issues 1 Pull Requests Actions Packages Projects Releases 1 Wiki Activity

tons more work on modularizing the code

Browse Source
This commit is contained in:
Elaina Claus
2024-10-05 18:55:00 -04:00
parent 5440a1ae61
commit 8f95c8f267
19 changed files with 360 additions and 296 deletions
Download Patch File Download Diff File Expand all files Collapse all files

173
src/vbr/vbr.nasm
View File

@@ -30,36 +30,59 @@ phy_ebpb_start:
; fill eBPB area with 0x00 since we skip writing this part to disk
times 54 db 0x00
; ###############
;
; Headers/Includes/Definitions
;
; ###############
%define __STEVIA_VBR
%include "cdecl16.inc"
%include "entry.inc"
%include "config.inc"
%include "mem.inc"
%include "error_codes.inc"
%include "fat32/bpb_offset_bx.inc"
; ###############
; End Section
; ###############
ALIGN 4, db 0x90
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, EARLY_STACK_START ; Setup stack
mov sp, EARLY_STACK_START ; Setup stack
mov bp, sp ; base ptr = stack ptr
sub sp, 0x20 ; local varible space
mov bx, VBR_ENTRY ; move Bx to the new start of the initial boot sector
sti ; all done with inital setup and relocation, reenable interupts
jmp 0:main ; fix up cs:ip just in case and jump to relocated code
nop
%include "config.inc"
%include "memory.inc"
; ###############
;
; Extra/Shared Functions
;
; ###############
%include "kmem_func.inc"
%include "partition_table.inc"
%include "errors.inc"
%include "util/error_func.inc"
%include "fat32/bpb.inc"
; ###############
; End Section
; ###############
ALIGN 4, db 0x90
main:
mov [bsDriveNumber], dl ; BIOS passes drive number in DL
mov [partition_offset], si ; save passed partition entry offset
mov byte [bp - 2], dl ; boot_drive
mov [bp - 4], si ; part_offset
.check_FAT_size: ; we only support a very specific setup of FAT32
cmp dword [bsSectorHuge], 0 ; SectorsHuge will not be set if FAT12/16
@@ -69,24 +92,39 @@ main:
; read sectors 1-63 to stage2 entry point
.load_stage2:
xor ax, ax
push ax ; upper_lower_lba = 0
mov ax, (fat32_bpb_SIZE + fat32_ebpb_SIZE) ; size in byte
push ax
mov ax, (phy_bpb_start - 0x3) ; start of bpb - 0x3 for the jump short main at the start
push ax
mov ax, fat32_bpb ; defined in memory.inc, destination
push ax
call kmemcpy ; copy bpb to memory
add sp, 0x6
mov ax , 1
push ax ; lower_lower_lba = 1
mov bx, fat32_bpb ; bx now points to aligned memory structure
movzx ax, byte [bp - 2]
push ax ; drive_num
mov ax, STAGE2_SECTOR_COUNT
push ax ; count
mov dword eax, 0x1
push dword eax ; lba
xor ax, ax
push ax ; offset = 0
push ax ; offset = 0
; 07E0:0
; 07E0:0 = 0x00007e00
mov ax, STAGE2_ENTRY
shr ax, 4
push ax ; segment = 7E0
push ax ; segment = 7E0
;uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
; uint16_t lower_lower_lba, uint16_t upper_lower_lba)
call read_stage2_raw
add sp, 0x8
; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
; uint32_t lba,
; uint16_t count, uint16_t drive_num)
call read_disk_raw
add sp, 0xC
.check_sig:
mov ax, 0x7E0
@@ -97,97 +135,16 @@ main:
ERROR VBR_ERROR_NO_SIGNATURE ; no signature present in stage2
.sig_ok:
mov ax, fat32_bpb_SIZE ; size in byte
push ax
mov ax, phy_bpb_start ; start of bpb
push ax
mov ax, fat32_bpb ; defined in memory.inc, destination
push ax
call kmemcpy ; copy bpb to memory
add sp, 0x6
mov ax, fat32_ebpb_SIZE ; 72 bytes of data
push ax
mov ax, phy_ebpb_start ; start of ebpb
push ax
mov ax, fat32_ebpb ; defined in memory.inc, destination
push ax
call kmemcpy ; copy ebpb to memory
add sp, 0x6
mov si, [partition_offset]
mov dl, [bsDriveNumber]
mov si, [bp - 4]
mov dx, [bp - 2]
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
; Required BIOS functions
;
; 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)
read_stage2_raw:
__CDECL16_ENTRY
.func:
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
add sp, 0x06
mov byte [lba_packet + LBAPkt_t.size], 0x10
mov word [lba_packet + LBAPkt_t.xfer_size], STAGE2_SECTOR_COUNT
mov ax, [bp + 10]
shl eax, 16
mov ax, [bp + 8]
mov dword [lba_packet + LBAPkt_t.lower_lba], eax
mov ax, [bp + 6]
mov word [lba_packet + LBAPkt_t.offset], ax
mov ax, [bp + 4]
mov word [lba_packet + LBAPkt_t.segment], ax
mov si, lba_packet
mov ah, 0x42
mov dl, byte [bsDriveNumber]
int 0x13
jnc .endf
ERROR VBR_ERROR_DISK_READ_ERR
.endf:
__CDECL16_EXIT
ret
; Data
; #############
;
; Locals
;
; #############
; offset from the begining of sector 0 to the active partition.
partition_offset:
dw 0x0000
; ###############
%include 'BIOS/func/ext_read.inc'
%assign bytes_remaining (420 - ($ - $$))
%warning VBR has bytes_remaining bytes remaining for code (MAX: 420 bytes)