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 :cpp:class:`sdmmc_slot_config_t` structure before calling :cpp:func:`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.
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.
Both slots :c:macro:`SDMMC_HOST_SLOT_0` and :c:macro:`SDMMC_HOST_SLOT_1` support 1-, 4- and 8-line SD interfaces. The slots are connected to {IDF_TARGET_NAME} GPIOs using the GPIO matrix. This means that any GPIO may be used for each of the SD card signals.
Other functions, such as the ones given below, will be called by the SD/MMC protocol layer via function pointers in the :cpp:class:`sdmmc_host_t` structure:
With the default initializers for :cpp:class:`sdmmc_host_t` and :cpp:class:`sdmmc_slot_config_t`, i.e., :c:macro:`SDMMC_HOST_DEFAULT` and :c:macro:`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 :cpp:class:`sdmmc_host_t`:
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``.
{IDF_TARGET_NAME} SDMMC Host can be configured to use arbitrary GPIOs for each of the signals. Configuration is performed by setting members of :cpp:class:`sdmmc_slot_config_t` structure.
For example, to use GPIOs 1-6 for CLK, CMD, and D0-D3 signals respectively:
Once :cpp:class:`sdmmc_slot_config_t` structure is initialized this way, you can use it when calling :cpp:func:`sdmmc_host_init_slot` or one of the higher level functions (such as :cpp:func:`esp_vfs_fat_sdmmc_mount`).
DDR mode places higher requirements for signal integrity. To disable DDR mode while keeping the :c:macro:`SDMMC_FREQ_HIGHSPEED` frequency, clear the :c:macro:`SDMMC_HOST_FLAG_DDR` bit in :cpp:member:`sdmmc_host_t::flags` field of the :cpp:class:`sdmmc_host_t`:
