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121 lines
5.1 KiB
Python
121 lines
5.1 KiB
Python
# SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
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# SPDX-License-Identifier: Apache-2.0
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from typing import Dict, Optional
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from construct import Int16ul
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from .fatfs_state import FATFSState
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from .utils import (FAT12, FAT16, build_byte, clean_first_half_byte, clean_second_half_byte,
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split_by_half_byte_12_bit_little_endian)
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class Cluster:
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"""
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class Cluster handles values in FAT table and allocates sectors in data region.
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"""
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RESERVED_BLOCK_ID: int = 0
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ROOT_BLOCK_ID: int = 1
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ALLOCATED_BLOCK_FAT12: int = 0xFFF
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ALLOCATED_BLOCK_FAT16: int = 0xFFFF
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ALLOCATED_BLOCK_SWITCH = {FAT12: ALLOCATED_BLOCK_FAT12, FAT16: ALLOCATED_BLOCK_FAT16}
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INITIAL_BLOCK_SWITCH: Dict[int, int] = {FAT12: 0xFF8, FAT16: 0xFFF8}
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def __init__(self,
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cluster_id: int,
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fatfs_state: FATFSState,
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is_empty: bool = True) -> None:
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self.id: int = cluster_id
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self.fatfs_state: FATFSState = fatfs_state
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self._next_cluster = None # type: Optional[Cluster]
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if self.id == Cluster.RESERVED_BLOCK_ID:
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self.is_empty = False
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self.set_in_fat(self.INITIAL_BLOCK_SWITCH[self.fatfs_state.fatfs_type])
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return
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self.cluster_data_address: int = self._compute_cluster_data_address()
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self.is_empty = is_empty
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assert self.cluster_data_address or self.is_empty
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@property
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def next_cluster(self): # type: () -> Optional[Cluster]
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return self._next_cluster
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@next_cluster.setter
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def next_cluster(self, value): # type: (Optional[Cluster]) -> None
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self._next_cluster = value
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def _cluster_id_to_logical_position_in_bits(self, _id: int) -> int:
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# computes address of the cluster in fat table
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return self.fatfs_state.fatfs_type * _id # type: ignore
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def _compute_cluster_data_address(self) -> int:
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if self.id == Cluster.ROOT_BLOCK_ID:
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return self.fatfs_state.root_directory_start # type: ignore
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# the first data cluster id is 2 (we have to subtract reserved cluster and cluster for root)
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return self.fatfs_state.sector_size * (self.id - 2) + self.fatfs_state.data_region_start # type: ignore
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def _set_first_half_byte(self, address: int, value: int) -> None:
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clean_second_half_byte(self.fatfs_state.binary_image, address)
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self.fatfs_state.binary_image[address] |= value << 4
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def _set_second_half_byte(self, address: int, value: int) -> None:
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clean_first_half_byte(self.fatfs_state.binary_image, address)
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self.fatfs_state.binary_image[address] |= value
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@property
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def fat_cluster_address(self) -> int:
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"""Determines how many bits precede the first bit of the cluster in FAT"""
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return self._cluster_id_to_logical_position_in_bits(self.id)
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@property
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def real_cluster_address(self) -> int:
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return self.fatfs_state.start_address + self.fat_cluster_address // 8 # type: ignore
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def set_in_fat(self, value: int) -> None:
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"""
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Sets cluster in FAT to certain value.
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Firstly, we split the target value into 3 half bytes (max value is 0xfff).
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Then we could encounter two situations:
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1. if the cluster index (indexed from zero) is even, we set the full byte computed by
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self.cluster_id_to_logical_position_in_bits and the second half of the consequent byte.
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Order of half bytes is 2, 1, 3.
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2. if the cluster index is odd, we set the first half of the computed byte and the full consequent byte.
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Order of half bytes is 1, 3, 2.
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"""
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# value must fit into number of bits of the fat (12, 16 or 32)
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assert value <= (1 << self.fatfs_state.fatfs_type) - 1
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half_bytes = split_by_half_byte_12_bit_little_endian(value)
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if self.fatfs_state.fatfs_type == FAT12:
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if self.fat_cluster_address % 8 == 0:
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self.fatfs_state.binary_image[self.real_cluster_address] = build_byte(half_bytes[1], half_bytes[0])
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self._set_second_half_byte(self.real_cluster_address + 1, half_bytes[2])
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elif self.fat_cluster_address % 8 != 0:
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self._set_first_half_byte(self.real_cluster_address, half_bytes[0])
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self.fatfs_state.binary_image[self.real_cluster_address + 1] = build_byte(half_bytes[2], half_bytes[1])
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elif self.fatfs_state.fatfs_type == FAT16:
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self.fatfs_state.binary_image[self.real_cluster_address:self.real_cluster_address + 2] = Int16ul.build(
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value)
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@property
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def is_root(self) -> bool:
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return self.id == Cluster.ROOT_BLOCK_ID
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def allocate_cluster(self) -> None:
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"""
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This method sets bits in FAT table to `allocated` and clean the corresponding sector(s)
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"""
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self.is_empty = False
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self.set_in_fat(self.ALLOCATED_BLOCK_SWITCH[self.fatfs_state.fatfs_type])
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cluster_start = self.cluster_data_address
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dir_size = self.fatfs_state.get_dir_size(self.is_root)
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cluster_end = cluster_start + dir_size
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self.fatfs_state.binary_image[cluster_start:cluster_end] = dir_size * b'\x00'
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