fox32rom/ryfs.asm

264 lines
5.6 KiB
NASM

; RYFS routines
; file struct:
; file_disk: 1 byte
; file_first_sector: 2 bytes
; file_seek_offset: 4 bytes
; file_reserved: 1 byte
; open a file from a RYFS-formatted disk
; inputs:
; r0: pointer to file name string (8.3 format, for example "test txt" for test.txt)
; r1: disk ID
; r2: file struct: pointer to a blank file struct
; outputs:
; r0: first file sector
ryfs_open:
push r1
push r2
push r10
; r10: pointer to file struct entry
mov r10, r2
mov.8 [r10], r1 ; write file_disk
inc r10
push r0
mov r0, 1
mov r2, TEMP_SECTOR_BUF
call read_sector
pop r0
; point to the file name of the first directory entry
mov r1, TEMP_SECTOR_BUF
add r1, 20
mov r2, 11 ; compare 11 bytes
ryfs_open_find_dir_entry_loop:
call compare_memory_bytes
ifz jmp ryfs_open_found_dir_entry
add r1, 16 ; point to the file name in the next directory entry
jmp ryfs_open_find_dir_entry_loop ; FIXME: this never returns if the file wasn't found
ryfs_open_found_dir_entry:
sub r1, 4 ; point to first sector of this file
mov.16 [r10], [r1] ; write file_first_sector
add r10, 2
mov [r10], 0 ; write file_seek_offset
inc r10
mov.8 [r10], 0 ; write file_reserved
movz.16 r0, [r1]
pop r10
pop r2
pop r1
ret
; seek specified file to the specified offset
; inputs:
; r0: byte offset
; r1: pointer to file struct
; outputs:
; none
ryfs_seek:
push r1
add r1, 3
mov [r1], r0
pop r1
ret
; read specified number of bytes into the specified buffer
; inputs:
; r0: number of bytes to read
; r1: pointer to file struct
; r2: pointer to destination buffer
; outputs:
; none
ryfs_read:
push r0
push r1
push r2
push r3
push r4
push r5
push r10
push r11
push r12
; number_of_sectors_to_load = ceil(input r0, 506) / 506
; first, ceil the number of bytes to multiple of 506
; value_temp = value / 506
; if value % 506 != 0:
; value_temp++
; value_ceil = value_temp * 506
mov r10, r0
mov r11, r0
mov r12, 506
div r11, r12
rem r10, r12
ifnz inc r11
mul r11, r12
div r11, r12
mov r3, r11 ; r3: number_of_sectors_to_load
mov r10, r1
add r10, 3
mov r4, [r10]
mov r10, r4
mov r11, r4
mov r12, 506
div r11, r12
rem r10, r12
ifnz inc r11
mul r11, r12
div r11, r12
mov r4, r11 ; r4: number of sectors to traverse
; start_sector = traverse through linked sectors starting at file_struct.file_first_sector
push r0
push r1
push r2
mov r10, r1
; read the file's first sector into the temp buffer
movz.8 r1, [r10] ; file_disk
inc r10
movz.16 r0, [r10] ; file_first_sector
mov r31, r4
ryfs_read_traverse_sectors_loop:
mov r2, TEMP_SECTOR_BUF
call read_sector
mov r4, r0
add r2, 2 ; point to next sector number
movz.16 r0, [r2] ; load next sector number
cmp r31, 0 ; if we started at zero, then don't attempt to loop
ifnz loop ryfs_read_traverse_sectors_loop
pop r2
pop r1
pop r0
; r4: start_sector
; total_bytes_remaining = input r0
; this_sector = start_sector
; for range 0..number_of_sectors_to_load:
; load this_sector into temporary buffer
; bytes_to_load = if total_bytes_remaining >= 506
; 506
; else:
; total_bytes_remaining
; for range 0..bytes_to_load:
; load byte from temporary buffer into destination buffer
; this_sector = this_sector.next
mov r10, r0 ; r10: total_bytes_remaining
ryfs_read_sector_loop:
push r0
push r1
push r2
; read this sector into the temp buffer
mov r0, r4
movz.8 r1, [r1] ; file_disk
mov r2, TEMP_SECTOR_BUF
call read_sector
pop r2
pop r1
pop r0
; r11: bytes_to_load
cmp r10, 506
ifgteq mov r11, 506
iflt mov r11, r10
push r0
push r1
push r2
; calculate the seek offset
mov r12, r1
add r12, 3
mov r5, [r12]
rem r5, 506
; copy the sector data to the destination buffer
mov r0, TEMP_SECTOR_BUF
add r0, 6
add r0, r5 ; add the seek offset
mov r1, r2
mov r2, r11
call copy_memory_bytes
pop r2
pop r1
pop r0
dec r10
ifnz jmp ryfs_read_sector_loop
; file_struct.file_seek_offset += input r0
add r1, 3
add [r1], r0
pop r12
pop r11
pop r10
pop r5
pop r4
pop r3
pop r2
pop r1
pop r0
ret
; read a whole file into the specified buffer
; FIXME: this will always load a multiple of 506 bytes, even if the file is smaller
; inputs:
; r0: pointer to file struct
; r1: pointer to destination buffer
; outputs:
; none
ryfs_read_whole_file:
push r0
push r1
push r2
push r10
push r11
mov r10, r0
mov r11, r1
; read the first sector into the temp buffer
movz.8 r1, [r0] ; file_disk
inc r0
movz.16 r0, [r0] ; file_first_sector
ryfs_read_whole_file_sector_loop:
mov r2, TEMP_SECTOR_BUF
call read_sector
; copy the sector data to the destination buffer
mov r0, TEMP_SECTOR_BUF
add r0, 6
mov r1, r11
mov r2, 506
call copy_memory_bytes
; check to see if this is the last sector
; FIXME: if this is the last sector, it should respect the sector size field in the header
sub r0, 4
cmp.16 [r0], 0
ifz jmp ryfs_read_whole_file_last_sector
; there are more sectors left, load them
movz.16 r0, [r0] ; sector number
mov r1, [r10] ; file_disk
add r11, 506
jmp ryfs_read_whole_file_sector_loop
ryfs_read_whole_file_last_sector:
pop r11
pop r10
pop r2
pop r1
pop r0
ret