MMC Driver

Overview

The SD/SDIO/MMC driver currently supports SD memory, SDIO cards, and eMMC chips. This is a protocol level driver built on top of SDMMC and SD SPI host drivers.

SDMMC and SD SPI host drivers (driver/sdmmc/include/driver/sdmmc_host.h and driver/spi/include/driver/sdspi_host.h) provide API functions for:

Sending commands to slave devices
Sending and receiving data
Handling error conditions within the bus

For functions used to initialize and configure:

SDMMC host, see SDMMC Host API
SD SPI host, see SD SPI Host API

The SDMMC protocol layer described in this document handles the specifics of the SD protocol, such as the card initialization and data transfer commands.

The protocol layer works with the host via the sdmmc_host_t structure. This structure contains pointers to various functions of the host.

Pin Configurations

..only:: SOC_SDMMC_USE_IOMUX and not SOC_SDMMC_USE_GPIO_MATRIX

SDMMC pins are dedicated, you don't have to configure the pins.

..only:: SOC_SDMMC_USE_GPIO_MATRIX and not SOC_SDMMC_USE_IOMUX

SDMMC pin signals are routed via GPIO Matrix, so you will need to configure the pins in sdmmc_slot_config_t.

..only:: esp32p4

SDMMC have two slots:

slot 0 pins are dedicated for UHS-I mode. This is not yet supported in the driver.

slot 1 pins are routed via GPIO Matrix, and it's for non UHS-I usage. You will need to configure the pins in sdmmc_slot_config_t to use the slot 1.

Application Example

An example which combines the SDMMC driver with the FATFS library is provided in the storage/sd_card directory of ESP-IDF examples. This example initializes the card, then writes and reads data from it using POSIX and C library APIs. See README.md file in the example directory for more information.

Combo (Memory + IO) Cards

The driver does not support SD combo cards. Combo cards are treated as IO cards.

Thread Safety

Most applications need to use the protocol layer only in one task. For this reason, the protocol layer does not implement any kind of locking on the sdmmc_card_t structure, or when accessing SDMMC or SD SPI host drivers. Such locking is usually implemented on a higher layer, e.g., in the filesystem driver.

Protocol Layer API

The protocol layer is given the sdmmc_host_t structure. This structure describes the SD/MMC host driver, lists its capabilities, and provides pointers to functions of the driver. The protocol layer stores card-specific information in the sdmmc_card_t structure. When sending commands to the SD/MMC host driver, the protocol layer uses the sdmmc_command_t structure to describe the command, arguments, expected return values, and data to transfer if there is any.

Using API with SD Memory Cards

To initialize the host, call the host driver functions, e.g., sdmmc_host_init(), sdmmc_host_init_slot().
To initialize the card, call sdmmc_card_init() and pass to it the parameters host - the host driver information, and card - a pointer to the structure sdmmc_card_t which will be filled with information about the card when the function completes.
To read and write sectors of the card, use sdmmc_read_sectors() and sdmmc_write_sectors() respectively and pass to it the parameter card - a pointer to the card information structure.
If the card is not used anymore, call the host driver function - e.g., sdmmc_host_deinit() - to disable the host peripheral and free the resources allocated by the driver.

Using API with eMMC Chips

From the protocol layer's perspective, eMMC memory chips behave exactly like SD memory cards. Even though eMMCs are chips and do not have a card form factor, the terminology for SD cards can still be applied to eMMC due to the similarity of the protocol (sdmmc_card_t, sdmmc_card_init). Note that eMMC chips cannot be used over SPI, which makes them incompatible with the SD SPI host driver.

To initialize eMMC memory and perform read/write operations, follow the steps listed for SD cards in the previous section.

Using API with SDIO Cards

Initialization and the probing process are the same as with SD memory cards. The only difference is in data transfer commands in SDIO mode.

During the card initialization and probing, performed with sdmmc_card_init(), the driver only configures the following registers of the IO card:

The IO portion of the card is reset by setting RES bit in the I/O Abort (0x06) register.
If 4-line mode is enabled in host and slot configuration, the driver attempts to set the Bus width field in the Bus Interface Control (0x07) register. If setting the filed is successful, which means that the slave supports 4-line mode, the host is also switched to 4-line mode.
If high-speed mode is enabled in the host configuration, the SHS bit is set in the High Speed (0x13) register.

In particular, the driver does not set any bits in (1) I/O Enable and Int Enable registers, (2) I/O block sizes, etc. Applications can set them by calling sdmmc_io_write_byte().

For card configuration and data transfer, choose the pair of functions relevant to your case from the table below.

Action	Read Function	Write Function
Read and write a single byte using IO_RW_DIRECT (CMD52)	`sdmmc_io_read_byte()`	`sdmmc_io_write_byte()`
Read and write multiple bytes using IO_RW_EXTENDED (CMD53) in byte mode	`sdmmc_io_read_bytes()`	`sdmmc_io_write_bytes()`
Read and write blocks of data using IO_RW_EXTENDED (CMD53) in block mode	`sdmmc_io_read_blocks()`	`sdmmc_io_write_blocks()`

SDIO interrupts can be enabled by the application using the function sdmmc_io_enable_int(). When using SDIO in 1-line mode, the D1 line also needs to be connected to use SDIO interrupts.

If you want the application to wait until the SDIO interrupt occurs, use sdmmc_io_wait_int().

API Reference

Header File

components/sdmmc/include/sdmmc_cmd.h
This header file can be included with:
#include "sdmmc_cmd.h"
This header file is a part of the API provided by the sdmmc component. To declare that your component depends on sdmmc, add the following to your CMakeLists.txt:
REQUIRES sdmmc
or
PRIV_REQUIRES sdmmc

Functions

esp_err_t sdmmc_card_init(const sdmmc_host_t *host, sdmmc_card_t *out_card)

Probe and initialize SD/MMC card using given host

Note

Only SD cards (SDSC and SDHC/SDXC) are supported now. Support for MMC/eMMC cards will be added later.

Parameters

host -- pointer to structure defining host controller
out_card -- pointer to structure which will receive information about the card when the function completes

Returns

ESP_OK on success
One of the error codes from SDMMC host controller

void sdmmc_card_print_info(FILE *stream, const sdmmc_card_t *card)

Print information about the card to a stream.

Parameters

stream -- stream obtained using fopen or fdopen
card -- card information structure initialized using sdmmc_card_init

esp_err_t sdmmc_get_status(sdmmc_card_t *card)

Get status of SD/MMC card

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init

Returns

ESP_OK on success
One of the error codes from SDMMC host controller

esp_err_t sdmmc_write_sectors(sdmmc_card_t *card, const void *src, size_t start_sector, size_t sector_count)

Write given number of sectors to SD/MMC card

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
src -- pointer to data buffer to read data from; data size must be equal to sector_count * card->csd.sector_size
start_sector -- sector where to start writing
sector_count -- number of sectors to write

Returns

ESP_OK on success or sector_count equal to 0
One of the error codes from SDMMC host controller

esp_err_t sdmmc_read_sectors(sdmmc_card_t *card, void *dst, size_t start_sector, size_t sector_count)

Read given number of sectors from the SD/MMC card

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
dst -- pointer to data buffer to write into; buffer size must be at least sector_count * card->csd.sector_size
start_sector -- sector where to start reading
sector_count -- number of sectors to read

Returns

ESP_OK on success or sector_count equal to 0
One of the error codes from SDMMC host controller

esp_err_t sdmmc_erase_sectors(sdmmc_card_t *card, size_t start_sector, size_t sector_count, sdmmc_erase_arg_t arg)

Erase given number of sectors from the SD/MMC card

Note

When sdmmc_erase_sectors used with cards in SDSPI mode, it was observed that card requires re-init after erase operation.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
start_sector -- sector where to start erase
sector_count -- number of sectors to erase
arg -- erase command (CMD38) argument

Returns

ESP_OK on success or sector_count equal to 0
One of the error codes from SDMMC host controller

esp_err_t sdmmc_can_discard(sdmmc_card_t *card)

Check if SD/MMC card supports discard

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init

Returns

ESP_OK if supported by the card/device
ESP_FAIL if not supported by the card/device

esp_err_t sdmmc_can_trim(sdmmc_card_t *card)

Check if SD/MMC card supports trim

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init

Returns

ESP_OK if supported by the card/device
ESP_FAIL if not supported by the card/device

esp_err_t sdmmc_mmc_can_sanitize(sdmmc_card_t *card)

Check if SD/MMC card supports sanitize

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init

Returns

ESP_OK if supported by the card/device
ESP_FAIL if not supported by the card/device

esp_err_t sdmmc_mmc_sanitize(sdmmc_card_t *card, uint32_t timeout_ms)

Sanitize the data that was unmapped by a Discard command

Note

Discard command has to precede sanitize operation. To discard, use MMC_DICARD_ARG with sdmmc_erase_sectors argument

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
timeout_ms -- timeout value in milliseconds required to sanitize the selected range of sectors.

Returns

ESP_OK on success
One of the error codes from SDMMC host controller

esp_err_t sdmmc_full_erase(sdmmc_card_t *card)

Erase complete SD/MMC card

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init

Returns

ESP_OK on success
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_read_byte(sdmmc_card_t *card, uint32_t function, uint32_t reg, uint8_t *out_byte)

Read one byte from an SDIO card using IO_RW_DIRECT (CMD52)

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
function -- IO function number
reg -- byte address within IO function
out_byte -- [out] output, receives the value read from the card

Returns

ESP_OK on success
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_write_byte(sdmmc_card_t *card, uint32_t function, uint32_t reg, uint8_t in_byte, uint8_t *out_byte)

Write one byte to an SDIO card using IO_RW_DIRECT (CMD52)

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
function -- IO function number
reg -- byte address within IO function
in_byte -- value to be written
out_byte -- [out] if not NULL, receives new byte value read from the card (read-after-write).

Returns

ESP_OK on success
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_read_bytes(sdmmc_card_t *card, uint32_t function, uint32_t addr, void *dst, size_t size)

Read multiple bytes from an SDIO card using IO_RW_EXTENDED (CMD53)

This function performs read operation using CMD53 in byte mode. For block mode, see sdmmc_io_read_blocks.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
function -- IO function number
addr -- byte address within IO function where reading starts
dst -- buffer which receives the data read from card
size -- number of bytes to read

Returns

ESP_OK on success
ESP_ERR_INVALID_SIZE if size exceeds 512 bytes
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_write_bytes(sdmmc_card_t *card, uint32_t function, uint32_t addr, const void *src, size_t size)

Write multiple bytes to an SDIO card using IO_RW_EXTENDED (CMD53)

This function performs write operation using CMD53 in byte mode. For block mode, see sdmmc_io_write_blocks.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
function -- IO function number
addr -- byte address within IO function where writing starts
src -- data to be written
size -- number of bytes to write

Returns

ESP_OK on success
ESP_ERR_INVALID_SIZE if size exceeds 512 bytes
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_read_blocks(sdmmc_card_t *card, uint32_t function, uint32_t addr, void *dst, size_t size)

Read blocks of data from an SDIO card using IO_RW_EXTENDED (CMD53)

This function performs read operation using CMD53 in block mode. For byte mode, see sdmmc_io_read_bytes.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
function -- IO function number
addr -- byte address within IO function where writing starts
dst -- buffer which receives the data read from card
size -- number of bytes to read, must be divisible by the card block size.

Returns

ESP_OK on success
ESP_ERR_INVALID_SIZE if size is not divisible by 512 bytes
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_write_blocks(sdmmc_card_t *card, uint32_t function, uint32_t addr, const void *src, size_t size)

Write blocks of data to an SDIO card using IO_RW_EXTENDED (CMD53)

This function performs write operation using CMD53 in block mode. For byte mode, see sdmmc_io_write_bytes.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
function -- IO function number
addr -- byte address within IO function where writing starts
src -- data to be written
size -- number of bytes to read, must be divisible by the card block size.

Returns

ESP_OK on success
ESP_ERR_INVALID_SIZE if size is not divisible by 512 bytes
One of the error codes from SDMMC host controller

esp_err_t sdmmc_io_enable_int(sdmmc_card_t *card)

Enable SDIO interrupt in the SDMMC host

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init

Returns

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if the host controller does not support IO interrupts

esp_err_t sdmmc_io_wait_int(sdmmc_card_t *card, TickType_t timeout_ticks)

Block until an SDIO interrupt is received

Slave uses D1 line to signal interrupt condition to the host. This function can be used to wait for the interrupt.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
timeout_ticks -- time to wait for the interrupt, in RTOS ticks

Returns

ESP_OK if the interrupt is received
ESP_ERR_NOT_SUPPORTED if the host controller does not support IO interrupts
ESP_ERR_TIMEOUT if the interrupt does not happen in timeout_ticks

esp_err_t sdmmc_io_get_cis_data(sdmmc_card_t *card, uint8_t *out_buffer, size_t buffer_size, size_t *inout_cis_size)

Get the data of CIS region of an SDIO card.

You may provide a buffer not sufficient to store all the CIS data. In this case, this function stores as much data into your buffer as possible. Also, this function will try to get and return the size required for you.

Parameters

card -- pointer to card information structure previously initialized using sdmmc_card_init
out_buffer -- Output buffer of the CIS data
buffer_size -- Size of the buffer.
inout_cis_size -- Mandatory, pointer to a size, input and output.
- input: Limitation of maximum searching range, should be 0 or larger than buffer_size. The function searches for CIS_CODE_END until this range. Set to 0 to search infinitely.
- output: The size required to store all the CIS data, if CIS_CODE_END is found.

Returns

ESP_OK: on success
ESP_ERR_INVALID_RESPONSE: if the card does not (correctly) support CIS.
ESP_ERR_INVALID_SIZE: CIS_CODE_END found, but buffer_size is less than required size, which is stored in the inout_cis_size then.
ESP_ERR_NOT_FOUND: if the CIS_CODE_END not found. Increase input value of inout_cis_size or set it to 0, if you still want to search for the end; output value of inout_cis_size is invalid in this case.
and other error code return from sdmmc_io_read_bytes

esp_err_t sdmmc_io_print_cis_info(uint8_t *buffer, size_t buffer_size, FILE *fp)

Parse and print the CIS information of an SDIO card.

Note

Not all the CIS codes and all kinds of tuples are supported. If you see some unresolved code, you can add the parsing of these code in sdmmc_io.c and contribute to the IDF through the Github repository.

         using sdmmc_card_init

Parameters

buffer -- Buffer to parse
buffer_size -- Size of the buffer.
fp -- File pointer to print to, set to NULL to print to stdout.

Returns

ESP_OK: on success
ESP_ERR_NOT_SUPPORTED: if the value from the card is not supported to be parsed.
ESP_ERR_INVALID_SIZE: if the CIS size fields are not correct.

Header File

components/driver/sdmmc/include/driver/sdmmc_types.h
This header file can be included with:
#include "driver/sdmmc_types.h"
This header file is a part of the API provided by the driver component. To declare that your component depends on driver, add the following to your CMakeLists.txt:
REQUIRES driver
or
PRIV_REQUIRES driver

Structures

struct sdmmc_csd_t

Decoded values from SD card Card Specific Data register

Public Members

int csd_ver: CSD structure format

int mmc_ver: MMC version (for CID format)

int capacity: total number of sectors

int sector_size: sector size in bytes

int read_block_len: block length for reads

int card_command_class: Card Command Class for SD

int tr_speed: Max transfer speed

struct sdmmc_cid_t

Decoded values from SD card Card IDentification register

Public Members

int mfg_id: manufacturer identification number

int oem_id: OEM/product identification number

char name[8]: product name (MMC v1 has the longest)

int revision: product revision

int serial: product serial number

int date: manufacturing date

struct sdmmc_scr_t

Decoded values from SD Configuration Register Note: When new member is added, update reserved bits accordingly

Public Members

uint32_t sd_spec: SD Physical layer specification version, reported by card

uint32_t erase_mem_state: data state on card after erase whether 0 or 1 (card vendor dependent)

uint32_t bus_width: bus widths supported by card: BIT(0) — 1-bit bus, BIT(2) — 4-bit bus

uint32_t reserved: reserved for future expansion

uint32_t rsvd_mnf: reserved for manufacturer usage

struct sdmmc_ssr_t

Decoded values from SD Status Register Note: When new member is added, update reserved bits accordingly

Public Members

uint32_t alloc_unit_kb: Allocation unit of the card, in multiples of kB (1024 bytes)

uint32_t erase_size_au: Erase size for the purpose of timeout calculation, in multiples of allocation unit

uint32_t cur_bus_width: SD current bus width

uint32_t discard_support: SD discard feature support

uint32_t fule_support: SD FULE (Full User Area Logical Erase) feature support

uint32_t erase_timeout: Timeout (in seconds) for erase of a single allocation unit

uint32_t erase_offset: Constant timeout offset (in seconds) for any erase operation

uint32_t reserved: reserved for future expansion

struct sdmmc_ext_csd_t

Decoded values of Extended Card Specific Data

Public Members

uint8_t rev: Extended CSD Revision

uint8_t power_class: Power class used by the card

uint8_t erase_mem_state: data state on card after erase whether 0 or 1 (card vendor dependent)

uint8_t sec_feature: secure data management features supported by the card

struct sdmmc_switch_func_rsp_t

SD SWITCH_FUNC response buffer

Public Members

uint32_t data[512 / 8 / sizeof(uint32_t)]: response data

struct sdmmc_command_t

SD/MMC command information

Public Members

uint32_t opcode: SD or MMC command index

uint32_t arg: SD/MMC command argument

sdmmc_response_t response: response buffer

void *data: buffer to send or read into

size_t datalen: length of data in the buffer

size_t buflen: length of the buffer

size_t blklen: block length

int flags: see below

esp_err_t error: error returned from transfer

uint32_t timeout_ms: response timeout, in milliseconds

struct sdmmc_host_t

SD/MMC Host description

This structure defines properties of SD/MMC host and functions of SD/MMC host which can be used by upper layers.

Public Members

uint32_t flags: flags defining host properties

int slot: slot number, to be passed to host functions

int max_freq_khz: max frequency supported by the host

float io_voltage: I/O voltage used by the controller (voltage switching is not supported)

esp_err_t (*init)(void): Host function to initialize the driver

esp_err_t (*set_bus_width)(int slot, size_t width): host function to set bus width

size_t (*get_bus_width)(int slot): host function to get bus width

esp_err_t (*set_bus_ddr_mode)(int slot, bool ddr_enable): host function to set DDR mode

esp_err_t (*set_card_clk)(int slot, uint32_t freq_khz): host function to set card clock frequency

esp_err_t (*set_cclk_always_on)(int slot, bool cclk_always_on): host function to set whether the clock is always enabled

esp_err_t (*do_transaction)(int slot, sdmmc_command_t *cmdinfo): host function to do a transaction

esp_err_t (*deinit)(void): host function to deinitialize the driver

esp_err_t (*deinit_p)(int slot): host function to deinitialize the driver, called with the slot

esp_err_t (*io_int_enable)(int slot): Host function to enable SDIO interrupt line

esp_err_t (*io_int_wait)(int slot, TickType_t timeout_ticks): Host function to wait for SDIO interrupt line to be active

int command_timeout_ms: timeout, in milliseconds, of a single command. Set to 0 to use the default value.

esp_err_t (*get_real_freq)(int slot, int *real_freq): Host function to provide real working freq, based on SDMMC controller setup

sdmmc_delay_phase_t input_delay_phase: input delay phase, this will only take into effect when the host works in SDMMC_FREQ_HIGHSPEED or SDMMC_FREQ_52M. Driver will print out how long the delay is

esp_err_t (*set_input_delay)(int slot, sdmmc_delay_phase_t delay_phase): set input delay phase

struct sdmmc_card_t

SD/MMC card information structure

Public Members

sdmmc_host_t host: Host with which the card is associated

uint32_t ocr: OCR (Operation Conditions Register) value

sdmmc_cid_t cid: decoded CID (Card IDentification) register value

sdmmc_response_t raw_cid: raw CID of MMC card to be decoded after the CSD is fetched in the data transfer mode

sdmmc_csd_t csd: decoded CSD (Card-Specific Data) register value

sdmmc_scr_t scr: decoded SCR (SD card Configuration Register) value

sdmmc_ssr_t ssr: decoded SSR (SD Status Register) value

sdmmc_ext_csd_t ext_csd: decoded EXT_CSD (Extended Card Specific Data) register value

uint16_t rca: RCA (Relative Card Address)

uint16_t max_freq_khz: Maximum frequency, in kHz, supported by the card

int real_freq_khz: Real working frequency, in kHz, configured on the host controller

uint32_t is_mem: Bit indicates if the card is a memory card

uint32_t is_sdio: Bit indicates if the card is an IO card

uint32_t is_mmc: Bit indicates if the card is MMC

uint32_t num_io_functions: If is_sdio is 1, contains the number of IO functions on the card

uint32_t log_bus_width: log2(bus width supported by card)

uint32_t is_ddr: Card supports DDR mode

uint32_t reserved: Reserved for future expansion

Macros

SDMMC_HOST_FLAG_1BIT: host supports 1-line SD and MMC protocol

SDMMC_HOST_FLAG_4BIT: host supports 4-line SD and MMC protocol

SDMMC_HOST_FLAG_8BIT: host supports 8-line MMC protocol

SDMMC_HOST_FLAG_SPI: host supports SPI protocol

SDMMC_HOST_FLAG_DDR: host supports DDR mode for SD/MMC

SDMMC_HOST_FLAG_DEINIT_ARG: host deinit function called with the slot argument

SDMMC_FREQ_DEFAULT: SD/MMC Default speed (limited by clock divider)

SDMMC_FREQ_HIGHSPEED: SD High speed (limited by clock divider)

SDMMC_FREQ_PROBING: SD/MMC probing speed

SDMMC_FREQ_52M: MMC 52MHz speed

SDMMC_FREQ_26M: MMC 26MHz speed

Type Definitions

typedef uint32_t sdmmc_response_t[4]: SD/MMC command response buffer

Enumerations

enum sdmmc_delay_phase_t

SD/MMC Host clock timing delay phases

This will only take effect when the host works in SDMMC_FREQ_HIGHSPEED or SDMMC_FREQ_52M. Driver will print out how long the delay is, in picosecond (ps).

Values:

enumerator SDMMC_DELAY_PHASE_0: Delay phase 0

enumerator SDMMC_DELAY_PHASE_1: Delay phase 1

enumerator SDMMC_DELAY_PHASE_2: Delay phase 2

enumerator SDMMC_DELAY_PHASE_3: Delay phase 3

enum sdmmc_erase_arg_t

SD/MMC erase command(38) arguments SD: ERASE: Erase the write blocks, physical/hard erase.

DISCARD: Card may deallocate the discarded blocks partially or completely. After discard operation the previously written data may be partially or fully read by the host depending on card implementation.

MMC: ERASE: Does TRIM, applies erase operation to write blocks instead of Erase Group.

DISCARD: The Discard function allows the host to identify data that is no longer required so that the device can erase the data if necessary during background erase events. Applies to write blocks instead of Erase Group After discard operation, the original data may be remained partially or fully accessible to the host dependent on device.

Values:

enumerator SDMMC_ERASE_ARG: Erase operation on SD, Trim operation on MMC

enumerator SDMMC_DISCARD_ARG: Discard operation for SD/MMC

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