kopia lustrzana https://github.com/espressif/esp-idf
50 wiersze
2.6 KiB
ReStructuredText
50 wiersze
2.6 KiB
ReStructuredText
Wear Levelling API
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==================
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:link_to_translation:`zh_CN:[中文]`
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Overview
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--------
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Most of flash memory and especially SPI flash that is used in {IDF_TARGET_NAME} has a sector-based organization and also has a limited number of erase/modification cycles per memory sector. The wear levelling component helps to distribute wear and tear among sectors more evenly without requiring any attention from the user.
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The wear levelling component provides API functions related to reading, writing, erasing, and memory mapping of data in external SPI flash through the partition component. The component also has higher-level API functions which work with the FAT filesystem defined in :doc:`FAT filesystem </api-reference/storage/fatfs>`.
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The wear levelling component, together with the FAT FS component, uses FAT FS sectors of 4096 bytes, which is a standard size for flash memory. With this size, the component shows the best performance but needs additional memory in RAM.
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To save internal memory, the component has two additional modes which both use sectors of 512 bytes:
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- **Performance mode.** Erase sector operation data is stored in RAM, the sector is erased, and then data is copied back to flash memory. However, if a device is powered off for any reason, all 4096 bytes of data is lost.
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- **Safety mode.** The data is first saved to flash memory, and after the sector is erased, the data is saved back. If a device is powered off, the data can be recovered as soon as the device boots up.
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The default settings are as follows:
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- Sector size is 512 bytes
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- Performance mode
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You can change the settings through the configuration menu.
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The wear levelling component does not cache data in RAM. The write and erase functions modify flash directly, and flash contents are consistent when the function returns.
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Wear Levelling access API functions
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-----------------------------------
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This is the set of API functions for working with data in flash:
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- ``wl_mount`` - initializes the wear levelling module and mounts the specified partition
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- ``wl_unmount`` - unmounts the partition and deinitializes the wear levelling module
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- ``wl_erase_range`` - erases a range of addresses in flash
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- ``wl_write`` - writes data to a partition
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- ``wl_read`` - reads data from a partition
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- ``wl_size`` - returns the size of available memory in bytes
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- ``wl_sector_size`` - returns the size of one sector
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As a rule, try to avoid using raw wear levelling functions and use filesystem-specific functions instead.
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Memory Size
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-----------
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The memory size is calculated in the wear levelling module based on partition parameters. The module uses some sectors of flash for internal data.
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