56 lines
2.7 KiB
ReStructuredText
56 lines
2.7 KiB
ReStructuredText
Wear Levelling APIs
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===================
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Overview
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--------
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Most of the flash devices and specially SPI flash devices that are used in ESP32
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have sector based organization and have limited amount of erase/modification cycles
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per memory sector. To avoid situation when one sector reach the limit of erases when
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other sectors was used not often, we have made a component that avoid this situation.
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The wear levelling component share the amount of erases between all sectors in the
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memory without user interaction.
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The wear_levelling component contains APIs related to reading, writing, erasing,
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memory mapping data in the external SPI flash through the partition component. It
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also has higher-level APIs which work with FAT filesystem defined in
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the :doc:`FAT filesystem </api-reference/storage/fatfs>`.
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The wear levelling component, together with FAT FS component, works with FAT FS sector size 4096
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bytes which is standard size of the flash devices. In this mode the component has best performance,
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but needs additional memoty in the RAM. To save internal memory the component has two additional modes
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to work with sector size 512 bytes: Performance and Safety modes. In Performance mode by erase sector
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operation data will be stored to the RAM, sector will be erased and then data will be stored
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back to the flash. If by this operation power off situation will occur, the complete 4096 bytes
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will be lost. To prevent this the Safety mode was implemented. In safety mode the data will be first
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stored to the flash and after sector will be erased, will be stored back. If power off situation will
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occur, after power on, the data will be recovered.
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By default defined the sector size 512 bytes and Performance mode. To change these values please use
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the configuration menu.
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The wear levelling component does not cache data in RAM. Write and erase functions
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modify flash directly, and flash contents is consistent when the function returns.
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Wear Levelling access APIs
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--------------------------
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This is the set of APIs for working with data in flash:
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- ``wl_mount`` mount wear levelling module for defined partition
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- ``wl_unmount`` used to unmount levelling module
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- ``wl_erase_range`` used to erase range of addresses in flash
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- ``wl_write`` used to write data to the partition
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- ``wl_read`` used to read data from the partition
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- ``wl_size`` return size of avalible memory in bytes
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- ``wl_sector_size`` returns size of one sector
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Generally, try to avoid using the raw wear levelling functions in favor of
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filesystem-specific functions.
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Memory Size
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-----------
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The memory size calculated in the wear Levelling module based on parameters of
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partition. The module use few sectors of flash for internal data.
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