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Storage API

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This section contains reference of the high-level storage APIs. They are based on low-level drivers such as SPI flash, SD/MMC.

  • Partitions API allow block based access to SPI flash according to the Partition Tables.

  • Non-Volatile Storage library (NVS) implements a fault-tolerant wear-levelled key-value storage in SPI NOR flash.

  • Virtual File System (VFS) library provides an interface for registration of file system drivers. SPIFFS, FAT and various other file system libraries are based on the VFS.

  • SPIFFS is a wear-levelled file system optimized for SPI NOR flash, well suited for small partition sizes and low throughput

  • FAT is a standard file system which can be used in SPI flash or on SD/MMC cards

  • Wear Levelling library implements a flash translation layer (FTL) suitable for SPI NOR flash. It is used as a container for FAT partitions in flash.

For information about storage security, please refer to Storage Security.

Note

It is suggested to use high-level APIs (esp_partition or file system) instead of low-level driver APIs to access the SPI NOR flash.

Due to the restriction of NOR flash and ESP hardware, accessing the main flash will affect the performance of the whole system. See SPI Flash API to learn more about the limitations.

Examples

NVS API examples

Code Example

Description

nvs_rw_blob

Shows the use of the C-style API to read and write blob data types in NVS flash.

nvs_rw_value

Shows the use of the C-style API to read and write integer data types in NVS flash.

nvs_rw_value_cxx

Shows the use of the C++-style API to read and write integer data types in NVS flash.

nvs_bootloader

Shows the use of the API available to the bootloader code to read NVS data.

nvsgen

Demonstrates how to use the Python-based NVS image generation tool to create an NVS partition image from the contents of a CSV file.
Common Filesystem API

Code Example

Description

fatfs/getting_started

Demonstrates basic common file API (stdio.h) usage over internal flash using FATFS.

fatfs/fs_operations

Demonstrates POSIX API for filesystem manipulation, such as moving, removing and renaming files.
FATFS API examples

Code Example

Description

fatfsgen

Demonstrates the capabilities of Python-based tooling for FATFS images available on host computers.

ext_flash_fatfs

Demonstrates using FATFS over wear leveling on external flash.

wear_leveling

Demonstrates using FATFS over wear leveling on internal flash.
SPIFFS API examples

Code Example

Description

spiffs

Shows the use of the SPIFFS API to initialize the filesystem and work with files using POSIX functions.

spiffsgen

Demonstrates the capabilities of Python-based tooling for SPIFFS images available on host computers.
Partition API examples

Code Example

Description

partition_api

Provides an overview of API functions to look up particular partitions, perform basic I/O operations, and use partitions via CPU memory mapping.

parttool

Demonstrates the capabilities of Python-based tooling for partition images available on host computers.
VFS related examples

Code Example

Description

littlefs

Shows the use of the LittleFS component to initialize the filesystem and work with a file using POSIX functions.

semihost_vfs

Demonstrates the use of the VFS API to let an ESP-based device access a file on a JTAG-connected host using POSIX functions.

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