SD/SDIO/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/include/driver/sdmmc_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:

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.

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.

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

  1. To initialize the host, call the host driver functions, e.g., sdmmc_host_init(), sdmmc_host_init_slot().
  2. 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.
  3. 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.
  4. 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 is 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:

  1. The IO portion of the card is reset by setting RES bit in the I/O Abort (0x06) register.
  2. 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.
  3. 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().

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.

API Reference

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.
Return
  • ESP_OK on success
  • One of the error codes from SDMMC host controller
Parameters
  • host: pointer to structure defining host controller
  • out_card: pointer to structure which will receive information about the card when the function completes

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_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

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

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

Write given number of sectors to SD/MMC card

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

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)

Return
  • ESP_OK on success
  • One of the error codes from SDMMC host controller
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: output, receives the value read from the card

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)

Return
  • ESP_OK on success
  • One of the error codes from SDMMC host controller
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: if not NULL, receives new byte value read from the card (read-after-write).

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.

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

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.

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

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.

Return
  • 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
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.

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.

Return
  • 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
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.

esp_err_t sdmmc_io_enable_int(sdmmc_card_t *card)

Enable SDIO interrupt in the SDMMC host

Return
  • ESP_OK on success
  • ESP_ERR_NOT_SUPPORTED if the host controller does not support IO interrupts
Parameters
  • card: pointer to card information structure previously initialized using sdmmc_card_init

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.

Return
  • 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
Parameters
  • card: pointer to card information structure previously initialized using sdmmc_card_init
  • timeout_ticks: time to wait for the interrupt, in RTOS ticks

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

Public Members

int sd_spec

SD Physical layer specification version, reported by card

int bus_width

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

struct sdmmc_ext_csd_t

Decoded values of Extended Card Specific Data

Public Members

uint8_t power_class

Power class used 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 buffer

size_t blklen

block length

int flags

see below

esp_err_t error

error returned from transfer

int 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 (*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 (*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.

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_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

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_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