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

rewrite InitFATDriver to use si/di/bx relative addresses

Browse Source
This commit is contained in:
Elaina Claus
2024-10-17 10:34:32 -04:00
parent b5cc1c9ec1
commit 85a8f0da1c
1 changed files with 33 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

55
include/fat32/FAT32_SYS.inc
View File

@@ -24,6 +24,8 @@
%include "fat32/bpb_offset_bx.inc"
%include "fat32/fat32_structures.inc"
; Clobbers: eax, edx
; returns: none
ALIGN 4, db 0x90
InitFATDriver:
__CDECL16_ENTRY
@@ -39,37 +41,44 @@ InitFATDriver:
.calc_active_part:
mov bx, [partition_offset_ptr]
mov ax, word [ds:bx]
mov cx, word [ds:bx]
mov ax, partition_table
add ax, cx
mov si, ax ; si = offset to active partition
mov dx, partition_table
add dx, ax ; dx points to the partition that was booted from
mov bx, dx ; set bx, should point at our partition
mov ax, fat32_state
mov di, ax
mov eax, dword [bx + PartEntry_t.lba_start]
mov dword [fat32_state + FAT32_State_t.active_drive_lba_32], eax
mov eax, dword [si + PartEntry_t.lba_start]
mov dword [di + FAT32_State_t.curr_drive_lba_32], eax
mov ax, fat32_bpb
mov si, ax
mov ax, fat32_ebpb
mov bx, ax
.calc_first_fat:
movzx eax, word [fat32_bpb + FAT32_bpb_t.reserved_sectors_16] ; first fat from start of partition
add eax, dword [fat32_state + FAT32_State_t.active_drive_lba_32] ; calculate offset from start of drive
movzx eax, word [si + FAT32_bpb_t.reserved_sectors_word] ; first fat from start of partition
add eax, dword [di + FAT32_State_t.curr_drive_lba_32] ; calculate offset from start of drive
jc InitFATDriver.error
mov dword [fat32_state + FAT32_State_t.first_fat_sector_32], eax
mov dword [di + FAT32_State_t.first_fat_sector_32], eax
.calc_total_fat:
mov ebx, dword [fat32_ebpb + FAT32_ebpb_t.sectors_per_fat_32]
movzx eax, byte [fat32_bpb + FAT32_bpb_t.fat_count_8]
mul ebx ; result in EDX:EAX, CF set on > 32bit return value
mov edx, dword [bx + FAT32_ebpb_t.FATSz_dword]
movzx eax, byte [si + FAT32_bpb_t.fat_count_byte]
mul edx ; result in EDX:EAX, CF set on > 32bit return value
jc InitFATDriver.error ; as a catch for unhandled overflow, just error if value is greater than 32bits
mov dword [fat32_state + FAT32_State_t.fat_size_32], eax
mov dword [di + FAT32_State_t.fat_size_32], eax
.calc_first_data:
mov edx, dword [fat32_state + FAT32_State_t.first_fat_sector_32]
mov edx, dword [di + FAT32_State_t.first_fat_sector_32]
add eax, edx
jc InitFATDriver.error
mov dword [fat32_state + FAT32_State_t.first_data_sector_32], eax
.get_first_root_dir:
mov eax, [fat32_ebpb + FAT32_ebpb_t.root_dir_cluster_32]
mov dword [fat32_state + FAT32_State_t.first_root_dir_sector_32], eax ; this only works when 1 cluster = 1 sector
mov dword [fat32_state + FAT32_State_t.active_dir_cluster_32], eax
mov dword [di + FAT32_State_t.first_data_sector_32], eax
.set_first_dir:
mov eax, dword [bx + FAT32_ebpb_t.root_clus_dword]
mov dword [di + FAT32_State_t.curr_dir_cluster_32], eax
.endp:
__CDECL16_EXIT
ret
@@ -108,7 +117,7 @@ SearchFATDIR:
print_string SearchFATDIR_INFO_cstr
.load_first_dir:
mov eax, dword [fat32_state + FAT32_State_t.active_dir_cluster_32]
mov eax, dword [fat32_state + FAT32_State_t.curr_dir_cluster_32]
push dword eax ; cluster
mov ax, dir_buffer
push ax ; offset
@@ -124,7 +133,7 @@ SearchFATDIR:
; if eax >= 0x0FFFFFF8 then there are no more clusters (end of chain)
; if eax == 0x0FFFFFF7 then this is a cluster that is marked as bad
mov eax, dword [fat32_state + FAT32_State_t.active_dir_cluster_32]
mov eax, dword [fat32_state + FAT32_State_t.curr_dir_cluster_32]
push dword eax
call NextCluster ; uint32_t NextCluster(uint32_t active_cluster);
add sp, 0x4
@@ -136,7 +145,7 @@ SearchFATDIR:
.load_next_dir_next_OK:
; load 512 bytes of directory entries from data sector
mov eax, [fat32_state + FAT32_State_t.active_dir_cluster_32]
mov eax, [fat32_state + FAT32_State_t.curr_dir_cluster_32]
push dword eax ; cluster
mov ax, dir_buffer