Storage Media

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Supported storage media list:

Name	Key Features	Application Scenarios	Capacity	Transmission Mode	Speed	Driver	Notes
SPI Flash	Can be shared with code, no additional cost	Parameter storage, text, image storage	MB	SPI	40/80 MHz 4-line	SPI Flash Driver
SD Card	Large capacity, pluggable	Audio, video file storage	GB	SDIO/SPI	20/40 MHz 1/4-line	SD/SDIO/MMC Driver for SD	*1
eMMC	Large capacity, high-speed read/write	Audio, video file storage	GB	SDIO	20/40 MHz 1/4/8-line	SD/SDIO/MMC Driver for eMMC	*2
USB Flash Drive	Large capacity, pluggable	Audio, video file storage	GB	USB	12 Mbps/480 Mbps	USB Host Driver	*3
EEPROM	Byte-addressable, low cost	Parameter storage	MB	I2C	100 ~ 400 kHz	eeprom driver

Note

• *1. SD card SDIO mode is only available on ESP chips that support SDIO host peripherals (such as ESP32, ESP32-S3);

• *2. Only available on ESP chips that support SDIO host peripherals (such as ESP32, ESP32-S3);

• *3. Only available on ESP chips that support USB-OTG peripherals (such as ESP32-S2, ESP32-S3).

SPI Flash

ESP series chips use NOR Flash by default to store user code and data. Flash can be integrated into modules or chips, with capacities typically of 4 MB, 8 MB, or 16 MB.

Users can use partition tables to partition Flash. Based on the functional division of partition tables, the main Flash designated space can be used as non-volatile storage (NVS) space to store application parameters, or mounted to file systems (FatFS, etc.) to store text, images and other files.

Flash chips support dual-line (DOUT/DIO) and quad-line (QOUT/QIO) operation modes, and can be configured to work in 40 MHz or 80 MHz modes. Since the main Flash chip can be used directly for data storage without additional storage chips, it is particularly suitable for applications with small capacity requirements (MB), high integration requirements, and cost sensitivity.

Note

For ESP-IDF v4.0 and above, the SPI Flash component not only supports using the main Flash for user data storage, but also supports connecting to a second external Flash chip for data storage.

Reference Documentation:

• SPI Flash API

• NVS Flash API

• FatFS API

Example Programs:

• storage/nvs: Use NVS for parameter storage;

• storage/fatfs: Use FatFS for file storage.

SD Card

ESP series chips support using SDIO interface or SPI interface to access SD cards. The SDIO interface supports 1-line, 4-line, or 8-line modes, supporting default rate of 20 MHz or high-speed rate of 40 MHz. It should be noted that the SDIO interface generally can only use fixed pins. The SPI interface supports specifying arbitrary IOs for SD cards through GPIO matrix, and can support access to multiple SD cards through CS pins. The SPI interface is more flexible in hardware design, but has lower access rates compared to the SDIO interface.

The SD/SDIO/MMC Driver in ESP-IDF provides protocol layer encapsulation based on the two access modes of SD cards, providing SD card initialization interfaces and protocol layer APIs. SD cards have the characteristics of large capacity and pluggability, and are widely used in application scenarios such as smart speakers and electronic photo albums that have large capacity storage requirements.

Reference Documentation:

• SD/SDIO/MMC Driver: Provides SD card initialization interfaces and protocol layer APIs;

• SDMMC Host Driver: Provides SDIO mode interface implementation;

• SD SPI Host Driver: Provides SPI mode interface implementation;

• When using SPI or 1-bit mode, please note the pin pull-up requirements.

Example Programs:

• storage/sd_card: Access SD card using FAT file system.

eMMC

eMMC (embedded MMC) memory chips have similar protocols to SD cards and can use the same driver SD/SDIO/MMC Driver. However, it should be noted that eMMC chips can only use SDIO mode and do not support SPI mode.

eMMC is generally soldered to the motherboard in chip form, with higher integration than SD cards, suitable for wearable devices and other scenarios that have large capacity storage requirements while having certain requirements for system integration.

Reference Documentation:

• SD/SDIO/MMC Driver;

• Supported eMMC Speed Modes.

Example Programs:

• storage/emmc: Access eMMC storage using FAT file system.

EEPROM

EEPROM (such as AT24C0X series) is a 1024-16384 bit serial electrically erasable memory (can also run in read-only mode by controlling pin levels), its storage space is generally distributed by word, with each word containing 8-bit space. EEPROM is byte-addressable, with simple read/write operations, particularly suitable for saving configuration parameters. After optimization, it can also be applied to industrial and commercial scenarios with certain requirements for power consumption and reliability.

Adapted EEPROM Chips:

Name	Function	Bus	Vendor	Datasheet	Driver
AT24C01/02	1024/2048 bits EEPROM	I2C	Atmel	Datasheet	AT24C02 driver

Frequently Asked Questions (FAQ)

• Please refer to: ESP-FAQ Storage Section

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