SD Card Utilities

Functions
esp_err_t	mount_sd_card (void)
	Mount the SD card with LittleFS.
void	sd_card_log_info (const sdmmc_card_t *card)
	Log information about a mounted SD card.
esp_err_t	unmount_sd_card (void)
	Unmount the SD card and release associated resources.

SD Card Macros
#define	SD_PWR_CTRL_LDO_IO_ID   (4)
	GPIO controlling SD power via LDO.
#define	GPIO_UNUSED   (-1)
	Placeholder for unused GPIO.
#define	SD_CARD_MOUNT_PATH   ("/littlefs")
	Path where SD card is mounted with VFS.
#define	SD_CARD_BUS_WIDTH   (4)
	SD card bus width.
#define	BYTE_DIV   (8)
	Divider to convert bits to bytes.

Detailed Description

Copyright

Copyright (c) 2026 Adrien Chevrier. Under AGPL-3.0-or-later license.

Useful ESP-IDF wrappers to initialize/deinitialize the file system on SD cards.

The OBC employs the fail-safe LittleFS file system. VFS is used to map standard POSIX calls to LittleFS functions.

Macro Definition Documentation

BYTE_DIV

#define BYTE_DIV   (8)

Divider to convert bits to bytes.

GPIO_UNUSED

#define GPIO_UNUSED   (-1)

Placeholder for unused GPIO.

SD_CARD_BUS_WIDTH

#define SD_CARD_BUS_WIDTH   (4)

SD card bus width.

SD_CARD_MOUNT_PATH

#define SD_CARD_MOUNT_PATH   ("/littlefs")

Path where SD card is mounted with VFS.

SD_PWR_CTRL_LDO_IO_ID

#define SD_PWR_CTRL_LDO_IO_ID   (4)

GPIO controlling SD power via LDO.

Function Documentation

mount_sd_card()

esp_err_t mount_sd_card

(

void

)

Mount the SD card with LittleFS.

The following steps are performed:

• SDMMC host creation and SDMMC slot configuration.
• Enabling on-chip LDO to power the SD card.
• SD card initialization.
• LittleFS configuration.
• Mouting the SD card with LittleFS.
• Cheking if the SD card has been mounted successfully.

Return values

ESP_OK	On success.
ESP_ERR_INVALID_ARG	Bad initialization for objects.
ESP_ERR_INVALID_STATE	Either the SDMMC host has not been configured or the partition is already mounted / is encrypted.
ESP_ERR_NO_MEM	Failed to allocate memory for objects.
ESP_ERR_NOT_FOUND	Partition for LittleFS was not found.
ESP_FAIL	Mount or format failed.

Note

This function provides detailed information / error logs.

Warning

This function must run inside a critical section.

sd_card_log_info()

void sd_card_log_info

(

const sdmmc_card_t *

card

)

Log information about a mounted SD card.

The following information is loged:

• Name.
• Type (SDIO, MMC, SDSC, SDHC, SDXC).
• Current speed and speed limit.
• Size.
• Version, sector size, capacity and read block lenght.
• Bus width.
• Specs specific to SD card types.

Parameters

[in]

card

Pointer to a SD card descriptor.

Warning

This function must run inside a critical section.

unmount_sd_card()

esp_err_t unmount_sd_card

(

void

)

Unmount the SD card and release associated resources.

Safely unmounts the LittleFS file system and powers down the SD card.

Return values

ESP_OK	On success.
ESP_ERR_INVALID_ARG	LDO instance is invalid.
ESP_ERR_INVALID_STATE	SDMMC host in not initialized or is unregistered.

Warning

This function must run inside a critical section.