On the ESP32, SDMMC host peripheral has two slots:
- Slot 0 (:c:macro:`SDMMC_HOST_SLOT_0`) is an 8-bit slot. It uses
HS1_*signals in the PIN MUX. - Slot 1 (:c:macro:`SDMMC_HOST_SLOT_1`) is a 4-bit slot. It uses
HS2_*signals in the PIN MUX.
Pin mappings of these slots are given in the following table:
Signal Slot 0 Slot 1 CMD GPIO11 GPIO15 CLK GPIO6 GPIO14 D0 GPIO7 GPIO2 D1 GPIO8 GPIO4 D2 GPIO9 GPIO12 D3 GPIO10 GPIO13 D4 GPIO16 D5 GPIO17 D6 GPIO5 D7 GPIO18 CD any input via GPIO matrix WP any input via GPIO matrix
Card Detect and Write Protect signals can be routed to arbitrary pins using GPIO matrix. To use these pins, set gpio_cd and gpio_wp members of :cpp:class:`sdmmc_slot_config_t` structure before calling :cpp:func:`sdmmc_host_init_slot`. Note that it is not advised to specify Card Detect pin when working with SDIO cards, because in ESP32 card detect signal can also trigger SDIO slave interrupt.
Warning
Pins used by slot 0 (HS1_*) are also used to connect SPI flash chip in ESP-WROOM32 and ESP32-WROVER modules. These pins can not be shared between SD card and SPI flash. If you need to use Slot 0, connect SPI flash to different pins and set Efuses accordingly.
SDMMC Host driver supports the following speed modes:
- Default Speed (20MHz), 4-line/1-line (with SD cards), and 8-line (with 3.3V eMMC).
- High Speed (40MHz), 4-line/1-line (with SD cards), and 8-line (with 3.3V eMMC)
- High Speed DDR (40MHz), 4-line (with 3.3V eMMC)
Not supported at present are:
- High Speed DDR mode, 8-line eMMC
- UHS-I 1.8V modes, 4-line SD cards
Of all the funtions listed below, only :cpp:func:`sdmmc_host_init`, :cpp:func:`sdmmc_host_init_slot`, and :cpp:func:`sdmmc_host_deinit` will be used directly by most applications.
Other functions, such as :cpp:func:`sdmmc_host_set_bus_width`, :cpp:func:`sdmmc_host_set_card_clk`, and :cpp:func:`sdmmc_host_do_transaction` will be called by the SD/MMC protocol layer via function pointers in :cpp:class:`sdmmc_host_t` structure.
With the default initializers for :cpp:class:`sdmmc_host_t` and :cpp:class:`sdmmc_slot_config_t` (:c:macro:`SDMMC_HOST_DEFAULT` and :c:macro:`SDMMC_SLOT_CONFIG_DEFAULT`), SDMMC Host driver will attempt to use widest bus supported by the card (4 lines for SD, 8 lines for eMMC) and 20MHz frequency.
In designs where communication at 40MHz frequency can be achieved, it is possible to increase the bus frequency to by changing max_freq_khz field of :cpp:class:`sdmmc_host_t`:
sdmmc_host_t host = SDMMC_HOST_DEFAULT(); host.max_freq_khz = SDMMC_FREQ_HIGHSPEED;
To configure bus width, set width field of :cpp:class:`sdmmc_slot_config_t`. For example, to set 1-line mode:
sdmmc_slot_config_t slot = SDMMC_SLOT_CONFIG_DEFAULT(); slot.width = 1;
See :doc:`SD/SDIO/MMC Driver <../storage/sdmmc>` for the higher level driver which implements the protocol layer.
See :doc:`SD SPI Host Driver <sdspi_host>` for a similar driver which uses SPI controller and is limited to SPI mode of SD protocol.
See :doc:`sd_pullup_requirements` for pullup support and compatiblities about modules and devkits.