SDMMC Host Driver

Overview

ESP32-S3’s SDMMC host peripheral has two slots. Each slot can be used independently to connect to an SD card, SDIO device or eMMC chip.

Both slots (SDMMC_HOST_SLOT_0, SDMMC_HOST_SLOT_1) support 1-, 4- and 8-line SD interface. The slots are connected to ESP32-S3 GPIOs using GPIO matrix. This means that any GPIO may be used for each of the SD card signals.

Supported Speed Modes

SDMMC Host driver supports the following speed modes:

Default Speed (20 MHz), 1/4-line (with SD cards), and 1/4/8-line (with 3.3 V eMMC)
High Speed (40 MHz), 1/4-line (with SD cards), and 1/4/8-line (with 3.3 V eMMC)
High Speed DDR (40 MHz), 4-line (with 3.3 V eMMC)

Speed modes not supported at present:

High Speed DDR mode, 8-line eMMC
UHS-I 1.8 V modes, 4-line SD cards

Using the SDMMC Host Driver

Of all the functions listed below, only the following ones will be used directly by most applications:

sdmmc_host_init()
sdmmc_host_init_slot()
sdmmc_host_deinit()

Other functions, such as the ones given below, will be called by the SD/MMC protocol layer via function pointers in the sdmmc_host_t structure:

sdmmc_host_set_bus_width()
sdmmc_host_set_card_clk()
sdmmc_host_do_transaction()

Configuring Bus Width and Frequency

With the default initializers for sdmmc_host_t and sdmmc_slot_config_t (SDMMC_HOST_DEFAULT and SDMMC_SLOT_CONFIG_DEFAULT), SDMMC Host driver will attempt to use the widest bus supported by the card (4 lines for SD, 8 lines for eMMC) and the frequency of 20 MHz.

In the designs where communication at 40 MHz frequency can be achieved, it is possible to increase the bus frequency by changing the max_freq_khz field of sdmmc_host_t:

sdmmc_host_t host = SDMMC_HOST_DEFAULT();
host.max_freq_khz = SDMMC_FREQ_HIGHSPEED;

If you need a specific frequency other than standard speeds, you are free to use any value from within appropriate range of the SD interface given (SDMMC or SDSPI). However, the real clock frequency shall be calculated by the underlying driver and the value can be different from the one required. For the SDMMC, max_freq_khz works as the upper limit so the final frequency value shall be always lower or equal. For the SDSPI, the nearest fitting frequency is supplied and thus the value can be greater than / equal to / lower than max_freq_khz.

To configure the bus width, set the width field of sdmmc_slot_config_t. For example, to set 1-line mode:

sdmmc_slot_config_t slot = SDMMC_SLOT_CONFIG_DEFAULT();
slot.width = 1;

Configuring GPIOs

ESP32-S3 SDMMC Host can be configured to use arbitrary GPIOs for each of the signals. Configuration is performed by setting members of sdmmc_slot_config_t structure. For example, to use GPIOs 1-6 for CLK, CMD, D0 - D3 signals, respectively:

sdmmc_slot_config_t slot = SDMMC_SLOT_CONFIG_DEFAULT();
slot.clk = GPIO_NUM_1;
slot.cmd = GPIO_NUM_2;
slot.d0 = GPIO_NUM_3;
slot.d1 = GPIO_NUM_4;
slot.d2 = GPIO_NUM_5;
slot.d3 = GPIO_NUM_6;

It is also possible to configure Card Detect and Write Protect pins. Similar to other signals, set cd and wp members of the same structure:

slot.cd = GPIO_NUM_7;
slot.wp = GPIO_NUM_8;

SDMMC_SLOT_CONFIG_DEFAULT sets both to GPIO_NUM_NC, meaning that by default the signals are not used.

Once sdmmc_slot_config_t structure is initialized this way, you can use it when calling sdmmc_host_init_slot() or one of the higher level functions, such as esp_vfs_fat_sdmmc_mount().

DDR Mode for eMMC chips

By default, DDR mode will be used if:

SDMMC host frequency is set to SDMMC_FREQ_HIGHSPEED in sdmmc_host_t structure, and
eMMC chip reports DDR mode support in its CSD register

DDR mode places higher requirements for signal integrity. To disable DDR mode while keeping SDMMC_FREQ_HIGHSPEED frequency, clear SDMMC_HOST_FLAG_DDR bit in flags field of sdmmc_host_t:

sdmmc_host_t host = SDMMC_HOST_DEFAULT();
host.max_freq_khz = SDMMC_FREQ_HIGHSPEED;
host.flags &= ~SDMMC_HOST_FLAG_DDR;

API Reference

Header File

components/driver/sdmmc/include/driver/sdmmc_host.h

Functions

esp_err_t sdmmc_host_init(void)

Initialize SDMMC host peripheral.

Note

This function is not thread safe

Returns

ESP_OK on success
ESP_ERR_INVALID_STATE if sdmmc_host_init was already called
ESP_ERR_NO_MEM if memory can not be allocated

esp_err_t sdmmc_host_init_slot(int slot, const sdmmc_slot_config_t *slot_config)

Initialize given slot of SDMMC peripheral.

On the ESP32, SDMMC peripheral has two slots:

Slot 0: 8-bit wide, maps to HS1_* signals in PIN MUX
Slot 1: 4-bit wide, maps to HS2_* signals in PIN MUX

Card detect and write protect signals can be routed to arbitrary GPIOs using GPIO matrix.

Note

This function is not thread safe

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
slot_config – additional configuration for the slot

Returns

ESP_OK on success
ESP_ERR_INVALID_STATE if host has not been initialized using sdmmc_host_init

esp_err_t sdmmc_host_set_bus_width(int slot, size_t width)

Select bus width to be used for data transfer.

SD/MMC card must be initialized prior to this command, and a command to set bus width has to be sent to the card (e.g. SD_APP_SET_BUS_WIDTH)

Note

This function is not thread safe

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
width – bus width (1, 4, or 8 for slot 0; 1 or 4 for slot 1)

Returns

ESP_OK on success
ESP_ERR_INVALID_ARG if slot number or width is not valid

size_t sdmmc_host_get_slot_width(int slot)

Get bus width configured in sdmmc_host_init_slot to be used for data transfer.

Parameters: slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
Returns: configured bus width of the specified slot.

esp_err_t sdmmc_host_set_card_clk(int slot, uint32_t freq_khz)

Set card clock frequency.

Currently only integer fractions of 40MHz clock can be used. For High Speed cards, 40MHz can be used. For Default Speed cards, 20MHz can be used.

Note

This function is not thread safe

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
freq_khz – card clock frequency, in kHz

Returns

ESP_OK on success
other error codes may be returned in the future

esp_err_t sdmmc_host_set_bus_ddr_mode(int slot, bool ddr_enabled)

Enable or disable DDR mode of SD interface.

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
ddr_enabled – enable or disable DDR mode

Returns

ESP_OK on success
ESP_ERR_NOT_SUPPORTED if DDR mode is not supported on this slot

esp_err_t sdmmc_host_set_cclk_always_on(int slot, bool cclk_always_on)

Enable or disable always-on card clock When cclk_always_on is false, the host controller is allowed to shut down the card clock between the commands. When cclk_always_on is true, the clock is generated even if no command is in progress.

Parameters

slot – slot number
cclk_always_on – enable or disable always-on clock

Returns

ESP_OK on success
ESP_ERR_INVALID_ARG if the slot number is invalid

esp_err_t sdmmc_host_do_transaction(int slot, sdmmc_command_t *cmdinfo)

Send command to the card and get response.

This function returns when command is sent and response is received, or data is transferred, or timeout occurs.

Attention: Data buffer passed in cmdinfo->data must be in DMA capable memory

Note

This function is not thread safe w.r.t. init/deinit functions, and bus width/clock speed configuration functions. Multiple tasks can call sdmmc_host_do_transaction as long as other sdmmc_host_* functions are not called.

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
cmdinfo – pointer to structure describing command and data to transfer

Returns

ESP_OK on success
ESP_ERR_TIMEOUT if response or data transfer has timed out
ESP_ERR_INVALID_CRC if response or data transfer CRC check has failed
ESP_ERR_INVALID_RESPONSE if the card has sent an invalid response
ESP_ERR_INVALID_SIZE if the size of data transfer is not valid in SD protocol
ESP_ERR_INVALID_ARG if the data buffer is not in DMA capable memory

esp_err_t sdmmc_host_io_int_enable(int slot)

Enable IO interrupts.

This function configures the host to accept SDIO interrupts.

Parameters: slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
Returns: returns ESP_OK, other errors possible in the future

esp_err_t sdmmc_host_io_int_wait(int slot, TickType_t timeout_ticks)

Block until an SDIO interrupt is received, or timeout occurs.

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
timeout_ticks – number of RTOS ticks to wait for the interrupt

Returns

ESP_OK on success (interrupt received)
ESP_ERR_TIMEOUT if the interrupt did not occur within timeout_ticks

esp_err_t sdmmc_host_deinit(void)

Disable SDMMC host and release allocated resources.

Note

This function is not thread safe

Returns

ESP_OK on success
ESP_ERR_INVALID_STATE if sdmmc_host_init function has not been called

esp_err_t sdmmc_host_get_real_freq(int slot, int *real_freq_khz)

Provides a real frequency used for an SD card installed on specific slot of SD/MMC host controller.

This function calculates real working frequency given by current SD/MMC host controller setup for required slot: it reads associated host and card dividers from corresponding SDMMC registers, calculates respective frequency and stores the value into the ‘real_freq_khz’ parameter

Parameters

slot – slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)
real_freq_khz – [out] output parameter for the result frequency (in kHz)

Returns

ESP_OK on success
ESP_ERR_INVALID_ARG on real_freq_khz == NULL or invalid slot number used

Structures

struct sdmmc_slot_config_t

Extra configuration for SDMMC peripheral slot

Public Members

gpio_num_t clk: GPIO number of CLK signal.

gpio_num_t cmd: GPIO number of CMD signal.

gpio_num_t d0: GPIO number of D0 signal.

gpio_num_t d1: GPIO number of D1 signal.

gpio_num_t d2: GPIO number of D2 signal.

gpio_num_t d3: GPIO number of D3 signal.

gpio_num_t d4: GPIO number of D4 signal. Ignored in 1- or 4- line mode.

gpio_num_t d5: GPIO number of D5 signal. Ignored in 1- or 4- line mode.

gpio_num_t d6: GPIO number of D6 signal. Ignored in 1- or 4- line mode.

gpio_num_t d7: GPIO number of D7 signal. Ignored in 1- or 4- line mode.

gpio_num_t gpio_cd: GPIO number of card detect signal.

gpio_num_t cd: GPIO number of card detect signal; shorter name.

gpio_num_t gpio_wp: GPIO number of write protect signal.

gpio_num_t wp: GPIO number of write protect signal; shorter name.

uint8_t width: Bus width used by the slot (might be less than the max width supported)

uint32_t flags: Features used by this slot.

Macros

SDMMC_HOST_SLOT_0: SDMMC slot 0.

SDMMC_HOST_SLOT_1: SDMMC slot 1.

SDMMC_HOST_DEFAULT()

Default sdmmc_host_t structure initializer for SDMMC peripheral.

Uses SDMMC peripheral, with 4-bit mode enabled, and max frequency set to 20MHz

SDMMC_SLOT_FLAG_INTERNAL_PULLUP: Enable internal pullups on enabled pins. The internal pullups are insufficient however, please make sure external pullups are connected on the bus. This is for debug / example purpose only.

SDMMC_SLOT_NO_CD: indicates that card detect line is not used

SDMMC_SLOT_NO_WP: indicates that write protect line is not used

SDMMC_SLOT_WIDTH_DEFAULT: use the maximum possible width for the slot

SDMMC_SLOT_CONFIG_DEFAULT(): Macro defining default configuration of SDMMC host slot

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SDMMC Host Driver

Overview

Supported Speed Modes

Using the SDMMC Host Driver

Configuring Bus Width and Frequency

Configuring GPIOs

DDR Mode for eMMC chips

See also

API Reference

Header File

Functions

Structures

Macros