# SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
# SPDX-License-Identifier: Apache-2.0
from typing import Dict, Optional
from construct import Int16ul
from .fatfs_state import BootSectorState
from .utils import (EMPTY_BYTE, FAT12, FAT16, build_byte, merge_by_half_byte_12_bit_little_endian,
split_by_half_byte_12_bit_little_endian)
def get_dir_size(is_root: bool, boot_sector: BootSectorState) -> int:
dir_size_: int = boot_sector.root_dir_sectors_cnt * boot_sector.sector_size if is_root else boot_sector.sector_size
return dir_size_
class Cluster:
"""
class Cluster handles values in FAT table and allocates sectors in data region.
"""
RESERVED_BLOCK_ID: int = 0
ROOT_BLOCK_ID: int = 1
ALLOCATED_BLOCK_FAT12: int = 0xFFF
ALLOCATED_BLOCK_FAT16: int = 0xFFFF
ALLOCATED_BLOCK_SWITCH = {FAT12: ALLOCATED_BLOCK_FAT12, FAT16: ALLOCATED_BLOCK_FAT16}
INITIAL_BLOCK_SWITCH: Dict[int, int] = {FAT12: 0xFF8, FAT16: 0xFFF8}
def __init__(self,
cluster_id: int,
boot_sector_state: BootSectorState,
init_: bool) -> None:
self.id: int = cluster_id
self.boot_sector_state: BootSectorState = boot_sector_state
self._next_cluster = None # type: Optional[Cluster]
# First cluster in FAT is reserved, low 8 bits contains BPB_Media and the rest is filled with 1
# e.g. the esp32 media type is 0xF8 thus the FAT[0] = 0xFF8 for FAT12, 0xFFF8 for FAT16
if self.id == Cluster.RESERVED_BLOCK_ID and init_:
self.set_in_fat(self.INITIAL_BLOCK_SWITCH[self.boot_sector_state.fatfs_type])
return
self.cluster_data_address: int = self._compute_cluster_data_address()
assert self.cluster_data_address
@property
def next_cluster(self): # type: () -> Optional[Cluster]
return self._next_cluster
@next_cluster.setter
def next_cluster(self, value): # type: (Optional[Cluster]) -> None
self._next_cluster = value
def _cluster_id_to_logical_position_in_bits(self, _id: int) -> int:
# computes address of the cluster in fat table
logical_position_: int = self.boot_sector_state.fatfs_type * _id
return logical_position_
@staticmethod
def compute_cluster_data_address(boot_sector_state: BootSectorState, id_: int) -> int:
"""
This method translates the id of the cluster to the address in data region.
:param boot_sector_state: the class with FS shared data
:param id_: id of the cluster
:returns: integer denoting the address of the cluster in the data region
"""
data_address_: int = boot_sector_state.root_directory_start
if not id_ == Cluster.ROOT_BLOCK_ID:
# the first data cluster id is 2 (we have to subtract reserved cluster and cluster for root)
data_address_ = boot_sector_state.sector_size * (id_ - 2) + boot_sector_state.data_region_start
return data_address_
def _compute_cluster_data_address(self) -> int:
return self.compute_cluster_data_address(self.boot_sector_state, self.id)
def _set_left_half_byte(self, address: int, value: int) -> None:
self.boot_sector_state.binary_image[address] &= 0x0f
self.boot_sector_state.binary_image[address] |= value << 4
def _set_right_half_byte(self, address: int, value: int) -> None:
self.boot_sector_state.binary_image[address] &= 0xf0
self.boot_sector_state.binary_image[address] |= value
@property
def fat_cluster_address(self) -> int:
"""Determines how many bits precede the first bit of the cluster in FAT"""
return self._cluster_id_to_logical_position_in_bits(self.id)
@property
def real_cluster_address(self) -> int:
"""
The property method computes the real address of the cluster in the FAT region. Result is simply
address of the cluster in fat + fat table address.
"""
cluster_address: int = self.boot_sector_state.fat_table_start_address + self.fat_cluster_address // 8
return cluster_address
def get_from_fat(self) -> int:
"""
Calculating the value in the FAT block, that denotes if the block is full, empty, or chained to other block.
For FAT12 is the block stored in one and half byte. If the order of the block is even the first byte and second
half of the second byte belongs to the block. First half of the second byte and the third byte belongs to
the second block.
e.g. b'\xff\x0f\x00' stores two blocks. First of them is evenly ordered (index 0) and is set to 0xfff,
that means full block that is final in chain of blocks
and second block is set to 0x000 that means empty block.
three bytes - AB XC YZ - stores two blocks - CAB YZX
"""
address_: int = self.real_cluster_address
bin_img_: bytearray = self.boot_sector_state.binary_image
if self.boot_sector_state.fatfs_type == FAT12:
if self.fat_cluster_address % 8 == 0:
# even block
return bin_img_[self.real_cluster_address] | ((bin_img_[self.real_cluster_address + 1] & 0x0F) << 8)
# odd block
return ((bin_img_[self.real_cluster_address] & 0xF0) >> 4) | (bin_img_[self.real_cluster_address + 1] << 4)
if self.boot_sector_state.fatfs_type == FAT16:
return int.from_bytes(bin_img_[address_:address_ + 2], byteorder='little')
raise NotImplementedError('Only valid fatfs types are FAT12 and FAT16.')
@property
def is_empty(self) -> bool:
"""
The property method takes a look into the binary array and checks if the bytes ordered by little endian
and relates to the current cluster are all zeros (which denotes they are empty).
"""
return self.get_from_fat() == 0x00
def set_in_fat(self, value: int) -> None:
"""
Sets cluster in FAT to certain value.
Firstly, we split the target value into 3 half bytes (max value is 0xfff).
Then we could encounter two situations:
1. if the cluster index (indexed from zero) is even, we set the full byte computed by
self.cluster_id_to_logical_position_in_bits and the second half of the consequent byte.
Order of half bytes is 2, 1, 3.
2. if the cluster index is odd, we set the first half of the computed byte and the full consequent byte.
Order of half bytes is 1, 3, 2.
"""
# value must fit into number of bits of the fat (12, 16 or 32)
assert value <= (1 << self.boot_sector_state.fatfs_type) - 1
half_bytes = split_by_half_byte_12_bit_little_endian(value)
bin_img_: bytearray = self.boot_sector_state.binary_image
if self.boot_sector_state.fatfs_type == FAT12:
assert merge_by_half_byte_12_bit_little_endian(*half_bytes) == value
if self.fat_cluster_address % 8 == 0:
# even block
bin_img_[self.real_cluster_address] = build_byte(half_bytes[1], half_bytes[0])
self._set_right_half_byte(self.real_cluster_address + 1, half_bytes[2])
elif self.fat_cluster_address % 8 != 0:
# odd block
self._set_left_half_byte(self.real_cluster_address, half_bytes[0])
bin_img_[self.real_cluster_address + 1] = build_byte(half_bytes[2], half_bytes[1])
elif self.boot_sector_state.fatfs_type == FAT16:
bin_img_[self.real_cluster_address:self.real_cluster_address + 2] = Int16ul.build(value)
assert self.get_from_fat() == value
@property
def is_root(self) -> bool:
return self.id == Cluster.ROOT_BLOCK_ID
def allocate_cluster(self) -> None:
"""
This method sets bits in FAT table to `allocated` and clean the corresponding sector(s)
"""
self.set_in_fat(self.ALLOCATED_BLOCK_SWITCH[self.boot_sector_state.fatfs_type])
cluster_start = self.cluster_data_address
dir_size = get_dir_size(self.is_root, self.boot_sector_state)
cluster_end = cluster_start + dir_size
self.boot_sector_state.binary_image[cluster_start:cluster_end] = dir_size * EMPTY_BYTE