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SDMMC Host Driver ​

Overview ​

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

  • Slot 0 (SDMMC_HOST_SLOT_0) is an 8-bit slot. It uses HS1_* signals in the PIN MUX.

  • Slot 1 (SDMMC_HOST_SLOT_1) is a 4-bit slot. It uses HS2_* signals in the PIN MUX.

The slots are connected to ESP32 GPIOs using IO MUX. Pin mappings of these slots are given in the table below.

SignalSlot 0Slot 1
CMDGPIO11GPIO15
CLKGPIO6GPIO14
D0GPIO7GPIO2
D1GPIO8GPIO4
D2GPIO9GPIO12
D3GPIO10GPIO13
D4GPIO16
D5GPIO17
D6GPIO5
D7GPIO18
CDany input via GPIO matrixany input via GPIO matrix
WPany input via GPIO matrixany input via GPIO matrix

The Card Detect (CD) and Write Protect (WP) signals can be routed to arbitrary pins using the GPIO matrix. To reserve the pins, set the cd and wp members of the sdmmc_slot_config_t structure before calling sdmmc_host_init_slot(). Please note that it is not advised to specify a CD pin when working with SDIO cards, because the CD signal in ESP32 can also trigger SDIO slave interrupt.

Warning

Pins used by Slot 0 (HS1_*) are also used to connect the SPI flash chip in ESP32-WROOM and ESP32-WROVER modules. These pins cannot be concurrently shared between an SD card and an SPI flash. If you need to use Slot 0, establish an alternative connection for the SPI flash using different pins and configure the necessary eFuses accordingly.

Supported Speed Modes ​

SDMMC Host driver supports the following speed modes:

  • Default Speed (20 MHz): 1-line or 4-line with SD cards, and 1-line, 4-line, or 8-line with 3.3 V eMMC

  • High Speed (40 MHz): 1-line or 4-line with SD cards, and 1-line, 4-line, or 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, i.e., 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 an 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;

DDR Mode for eMMC Chips ​

By default, DDR mode will be used if:

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

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

See also ​

  • SD/SDIO/MMC Driver: introduces the higher-level driver which implements the protocol layer.

  • SD SPI Host Driver: introduces a similar driver that uses the SPI controller and is limited to SD protocol's SPI mode.

  • SD Pull-up Requirements: introduces pull-up support and compatibilities of modules and development kits.

API Reference ​

Header File ​

#include "driver/sdmmc_host.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

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

esp_err_t sdmmc_host_set_input_delay(int slot, sdmmc_delay_phase_t delay_phase)

set input delay

  • This API sets delay when the SDMMC Host samples the signal from the SD Slave.

  • This API will check if the given delay_phase is valid or not.

  • This API will print out the delay time, in picosecond (ps)

Note

ESP32 doesn't support this feature, you will get an ESP_ERR_NOT_SUPPORTED

Parameters

  • slot -- slot number (SDMMC_HOST_SLOT_0 or SDMMC_HOST_SLOT_1)

  • delay_phase -- delay phase, this API will convert the phase into picoseconds and print it out

Returns

  • ESP_OK: ON success.

  • ESP_ERR_INVALID_ARG: Invalid argument.

  • ESP_ERR_NOT_SUPPORTED: ESP32 doesn't support this feature.

Structures ​

struct sdmmc_slot_config_t

Extra configuration for SDMMC peripheral slot

Public Members

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_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_FLAG_WP_ACTIVE_HIGH

GPIO write protect polarity. 0 means "active low", i.e. card is protected when the GPIO is low; 1 means "active high", i.e. card is protected when GPIO is high.

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