磨损均衡 API

[English]

概述

ESP32 所使用的 flash，特别是 SPI flash 多数具备扇区结构，且每个扇区仅允许有限次数的擦除/修改操作。为了避免过度使用某一扇区，乐鑫提供了磨损均衡组件，无需用户介入即可帮助用户均衡各个扇区之间的磨损。

磨损均衡组件包含了通过分区组件对外部 SPI flash 进行数据读取、写入、擦除和存储器映射相关的 API 函数。磨损均衡组件还具有软件上更高级别的 API 函数，与 FAT 文件系统 协同工作。

磨损均衡组件与 FAT 文件系统组件共用 FAT 文件系统的扇区，扇区大小为 4096 字节，是标准 flash 扇区的大小。在这种模式下，磨损均衡组件性能达到最佳，但需要在 RAM 中占用更多内存。

为了节省内存，磨损均衡组件还提供了另外两种模式，均使用 512 字节大小的扇区：

  • 性能模式：先将数据保存在 RAM 中，擦除扇区，然后将数据存储回 flash。如果设备在扇区擦写过程中突然断电，则整个扇区（4096 字节）数据将全部丢失。
  • 安全模式：数据先保存在 flash 中空余扇区，擦除扇区后，数据即存储回去。如果设备断电，上电后可立即恢复数据。

设备默认设置如下：

  • 定义扇区大小为 512 字节
  • 默认使用性能模式

您可以使用配置菜单更改设置。

磨损均衡组件不会将数据缓存在 RAM 中。写入和擦除函数直接修改 flash，函数返回后，flash 即完成修改。

磨损均衡访问 API

处理 flash 数据常用的 API 如下所示：

  • wl_mount - 为指定分区挂载并初始化磨损均衡模块
  • wl_unmount - 卸载分区并释放磨损均衡模块
  • wl_erase_range - 擦除 flash 中指定的地址范围
  • wl_write - 将数据写入分区
  • wl_read - 从分区读取数据
  • wl_size - 返回可用内存的大小（以字节为单位）
  • wl_sector_size - 返回一个扇区的大小

请尽量避免直接使用原始磨损均衡函数，建议您使用文件系统特定的函数。

内存大小

内存大小是根据分区参数在磨损均衡模块中计算所得，由于模块使用 flash 部分扇区存储内部数据，因此计算所得内存大小有少许偏差。

应用示例

storage/wear_levelling 中提供了一款磨损均衡驱动与 FatFs 库结合使用的示例。该示例初始化磨损均衡驱动，挂载 FAT 文件系统分区，并使用 POSIX（可移植操作系统接口）和 C 库 API 从中写入和读取数据。如需了解更多信息，请参考 storage/wear_levelling/README.md。

高级 API 参考

函数

esp_err_t esp_vfs_fat_spiflash_mount(const char *base_path, const char *partition_label, const esp_vfs_fat_mount_config_t *mount_config, wl_handle_t *wl_handle)

Convenience function to initialize FAT filesystem in SPI flash and register it in VFS.

This is an all-in-one function which does the following:

  • finds the partition with defined partition_label. Partition label should be configured in the partition table.
  • initializes flash wear levelling library on top of the given partition
  • mounts FAT partition using FATFS library on top of flash wear levelling library
  • registers FATFS library with VFS, with prefix given by base_prefix variable

This function is intended to make example code more compact.

Return
  • ESP_OK on success
  • ESP_ERR_NOT_FOUND if the partition table does not contain FATFS partition with given label
  • ESP_ERR_INVALID_STATE if esp_vfs_fat_spiflash_mount was already called
  • ESP_ERR_NO_MEM if memory can not be allocated
  • ESP_FAIL if partition can not be mounted
  • other error codes from wear levelling library, SPI flash driver, or FATFS drivers
Parameters
  • base_path: path where FATFS partition should be mounted (e.g. “/spiflash”)
  • partition_label: label of the partition which should be used
  • mount_config: pointer to structure with extra parameters for mounting FATFS
  • wl_handle: wear levelling driver handle

struct esp_vfs_fat_mount_config_t

Configuration arguments for esp_vfs_fat_sdmmc_mount and esp_vfs_fat_spiflash_mount functions.

Public Members

bool format_if_mount_failed

If FAT partition can not be mounted, and this parameter is true, create partition table and format the filesystem.

int max_files

Max number of open files.

size_t allocation_unit_size

If format_if_mount_failed is set, and mount fails, format the card with given allocation unit size. Must be a power of 2, between sector size and 128 * sector size. For SD cards, sector size is always 512 bytes. For wear_levelling, sector size is determined by CONFIG_WL_SECTOR_SIZE option.

Using larger allocation unit size will result in higher read/write performance and higher overhead when storing small files.

Setting this field to 0 will result in allocation unit set to the sector size.

esp_err_t esp_vfs_fat_spiflash_unmount(const char *base_path, wl_handle_t wl_handle)

Unmount FAT filesystem and release resources acquired using esp_vfs_fat_spiflash_mount.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_STATE if esp_vfs_fat_spiflash_mount hasn’t been called
Parameters
  • base_path: path where partition should be registered (e.g. “/spiflash”)
  • wl_handle: wear levelling driver handle returned by esp_vfs_fat_spiflash_mount

中层 API 参考

Functions

esp_err_t wl_mount(const esp_partition_t *partition, wl_handle_t *out_handle)

Mount WL for defined partition.

Return
  • ESP_OK, if the allocation was successfully;
  • ESP_ERR_INVALID_ARG, if WL allocation was unsuccessful;
  • ESP_ERR_NO_MEM, if there was no memory to allocate WL components;
Parameters
  • partition: that will be used for access
  • out_handle: handle of the WL instance

esp_err_t wl_unmount(wl_handle_t handle)

Unmount WL for defined partition.

Return
  • ESP_OK, if the operation completed successfully;
  • or one of error codes from lower-level flash driver.
Parameters
  • handle: WL partition handle

esp_err_t wl_erase_range(wl_handle_t handle, size_t start_addr, size_t size)

Erase part of the WL storage.

Return
  • ESP_OK, if the range was erased successfully;
  • ESP_ERR_INVALID_ARG, if iterator or dst are NULL;
  • ESP_ERR_INVALID_SIZE, if erase would go out of bounds of the partition;
  • or one of error codes from lower-level flash driver.
Parameters
  • handle: WL handle that are related to the partition
  • start_addr: Address where erase operation should start. Must be aligned to the result of function wl_sector_size(…).
  • size: Size of the range which should be erased, in bytes. Must be divisible by result of function wl_sector_size(…)..

esp_err_t wl_write(wl_handle_t handle, size_t dest_addr, const void *src, size_t size)

Write data to the WL storage.

Before writing data to flash, corresponding region of flash needs to be erased. This can be done using wl_erase_range function.

Note
Prior to writing to WL storage, make sure it has been erased with wl_erase_range call.
Return
  • ESP_OK, if data was written successfully;
  • ESP_ERR_INVALID_ARG, if dst_offset exceeds partition size;
  • ESP_ERR_INVALID_SIZE, if write would go out of bounds of the partition;
  • or one of error codes from lower-level flash driver.
Parameters
  • handle: WL handle that are related to the partition
  • dest_addr: Address where the data should be written, relative to the beginning of the partition.
  • src: Pointer to the source buffer. Pointer must be non-NULL and buffer must be at least ‘size’ bytes long.
  • size: Size of data to be written, in bytes.

esp_err_t wl_read(wl_handle_t handle, size_t src_addr, void *dest, size_t size)

Read data from the WL storage.

Return
  • ESP_OK, if data was read successfully;
  • ESP_ERR_INVALID_ARG, if src_offset exceeds partition size;
  • ESP_ERR_INVALID_SIZE, if read would go out of bounds of the partition;
  • or one of error codes from lower-level flash driver.
Parameters
  • handle: WL module instance that was initialized before
  • dest: Pointer to the buffer where data should be stored. Pointer must be non-NULL and buffer must be at least ‘size’ bytes long.
  • src_addr: Address of the data to be read, relative to the beginning of the partition.
  • size: Size of data to be read, in bytes.

size_t wl_size(wl_handle_t handle)

Get size of the WL storage.

Return
usable size, in bytes
Parameters
  • handle: WL module handle that was initialized before

size_t wl_sector_size(wl_handle_t handle)

Get sector size of the WL instance.

Return
sector size, in bytes
Parameters
  • handle: WL module handle that was initialized before

Macros

WL_INVALID_HANDLE

Type Definitions

typedef int32_t wl_handle_t

wear levelling handle

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