磨损均衡 API
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。
另请参阅
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
头文件
有关高级磨损均衡函数 esp_vfs_fat_spiflash_mount_rw_wl()、 esp_vfs_fat_spiflash_unmount_rw_wl() 和结构体 esp_vfs_fat_mount_config_t 的详细内容，请参见 FAT 文件系统。
中层 API 参考
Header File
This header file can be included with:
#include "wear_levelling.h"
- This header file is a part of the API provided by the
wear_levellingcomponent. To declare that your component depends onwear_levelling, add the following to your CMakeLists.txt:
REQUIRES wear_levellingor
> PRIV_REQUIRES wear_levelling
Functions
esp_err_t wl_mount(const esp_partition_t *partition, wl_handle_t *out_handle)
Mount WL for defined partition.
参数
partition -- that will be used for access
out_handle -- handle of the WL instance
返回
ESP_OK, if the WL allocation is successful;
ESP_ERR_INVALID_ARG, if the arguments for WL configuration are not valid;
ESP_ERR_NO_MEM, if the WL allocation fails because of insufficient memory;
esp_err_t wl_unmount(wl_handle_t handle)
Unmount WL for defined partition.
参数
handle -- WL partition handle
返回
ESP_OK, if the operation is successful;
or one of error codes from lower-level flash driver.
esp_err_t wl_erase_range(wl_handle_t handle, size_t start_addr, size_t size)
Erase part of the WL storage.
参数
handle -- WL handle that are related to the partition
start_addr -- Address from 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 the result of function wl_sector_size(...)..
返回
ESP_OK, if the given 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.
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.
备注
Prior to writing to WL storage, make sure it has been erased with wl_erase_range call.
参数
handle -- WL handle corresponding to the WL 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.
返回
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.
esp_err_t wl_read(wl_handle_t handle, size_t src_addr, void *dest, size_t size)
Read data from the WL storage.
参数
handle -- WL module instance that was initialized before
dest -- Pointer to the buffer where data should be stored. The Pointer must be non-NULL and the 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.
返回
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.
size_t wl_size(wl_handle_t handle)
Get the actual flash size in use for the WL storage partition.
参数
handle -- WL module handle that was initialized before
返回
usable size, in bytes
size_t wl_sector_size(wl_handle_t handle)
Get sector size of the WL instance.
参数
handle -- WL module handle that was initialized before
返回
sector size, in bytes
Macros
WL_INVALID_HANDLE
Type Definitions
typedef int32_t wl_handle_t
wear levelling handle