SD SPI Host Driver

Overview

The SD SPI host driver allows communicating with one or more SD cards by the SPI Master driver which makes use of the SPI host. Each card is accessed through an SD SPI device represented by an sdspi_dev_handle_t spi_handle returned when attaching the device to an SPI bus by calling sdspi_host_init_device. The bus should be already initialized before (by spi_bus_initialize).

This driver’s naming pattern was adopted from the SDMMC Host driver due to their similarity. Likewise, the APIs of both drivers are also very similar.

SD SPI driver (access the SD card in SPI mode) offers lower throughput but makes pin selection more flexible. With the help of the GPIO matrix, an SPI peripheral’s signals can be routed to any ESP32 pin. Otherwise, if SDMMC host driver is used (See SDMMC Host) to access the card in SD 1-bit/4-bit mode, higher throughput can be reached but it requires routing the signals through their dedicated IO_MUX pins only.

With the help of SPI Master driver based on, the SPI bus can be shared among SD cards and other SPI devices. The SPI Master driver will handle exclusive access from different tasks.

The SD SPI driver uses software-controlled CS signal.

How to Use

Firstly, use the macro SDSPI_DEVICE_CONFIG_DEFAULT to initialize a structure sdmmc_slot_config_t, which is used to initialize an SD SPI device. This macro will also fill in the default pin mappings, which is same as the pin mappings of SDMMC host driver. Modify the host and pins of the structure to desired value. Then call sdspi_host_init_device to initialize the SD SPI device and attach to its bus.

Then use SDSPI_HOST_DEFAULT macro to initialize a sdmmc_host_t structure, which is used to store the state and configurations of upper layer (SD/SDIO/MMC driver). Modify the slot parameter of the structure to the SD SPI device spi_handle just returned from sdspi_host_init_device. Call sdmmc_card_init with the sdmmc_host_t to probe and initialize the SD card.

Now you can use SD/SDIO/MMC driver functions to access your card!

Other Details

Only the following driver’s API functions are normally used by most applications:

Other functions are mostly used by the protocol level SD/SDIO/MMC driver via function pointers in the sdmmc_host_t structure. For more details, see the SD/SDIO/MMC Driver.

Note

SD over SPI does not support speeds above SDMMC_FREQ_DEFAULT due to the limitations of the SPI driver.

Warning

If you want to share the SPI bus among SD card and other SPI devices, there are some restrictions, see Sharing the SPI bus among SD card and other SPI devices.

API Reference

Header File

Functions

esp_err_t sdspi_host_init(void)

Initialize SD SPI driver.

Note

This function is not thread safe

Returns

  • ESP_OK on success

  • other error codes may be returned in future versions

esp_err_t sdspi_host_init_device(const sdspi_device_config_t *dev_config, sdspi_dev_handle_t *out_handle)

Attach and initialize an SD SPI device on the specific SPI bus.

Note

This function is not thread safe

Note

Initialize the SPI bus by spi_bus_initialize() before calling this function.

Note

The SDIO over sdspi needs an extra interrupt line. Call gpio_install_isr_service() before this function.

Parameters

  • dev_config – pointer to device configuration structure

  • out_handle – Output of the handle to the sdspi device.

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_ARG if sdspi_host_init_device has invalid arguments

  • ESP_ERR_NO_MEM if memory can not be allocated

  • other errors from the underlying spi_master and gpio drivers

esp_err_t sdspi_host_remove_device(sdspi_dev_handle_t handle)

Remove an SD SPI device.

Parameters

handle – Handle of the SD SPI device

Returns

Always ESP_OK

esp_err_t sdspi_host_do_transaction(sdspi_dev_handle_t handle, 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.

Note

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

Parameters

  • handle – Handle of the sdspi device

  • 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_t sdspi_host_set_card_clk(sdspi_dev_handle_t host, 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

  • host – Handle of the sdspi device

  • freq_khz – card clock frequency, in kHz

Returns

  • ESP_OK on success

  • other error codes may be returned in the future

esp_err_t sdspi_host_deinit(void)

Release resources allocated using sdspi_host_init.

Note

This function is not thread safe

Returns

  • ESP_OK on success

  • ESP_ERR_INVALID_STATE if sdspi_host_init function has not been called

esp_err_t sdspi_host_io_int_enable(sdspi_dev_handle_t handle)

Enable SDIO interrupt.

Parameters

handle – Handle of the sdspi device

Returns

  • ESP_OK on success

esp_err_t sdspi_host_io_int_wait(sdspi_dev_handle_t handle, TickType_t timeout_ticks)

Wait for SDIO interrupt until timeout.

Parameters

  • handle – Handle of the sdspi device

  • timeout_ticks – Ticks to wait before timeout.

Returns

  • ESP_OK on success

Structures

struct sdspi_device_config_t

Extra configuration for SD SPI device.

Public Members

spi_host_device_t host_id

SPI host to use, SPIx_HOST (see spi_types.h).

gpio_num_t gpio_cs

GPIO number of CS signal.

gpio_num_t gpio_cd

GPIO number of card detect signal.

gpio_num_t gpio_wp

GPIO number of write protect signal.

gpio_num_t gpio_int

GPIO number of interrupt line (input) for SDIO card.

Macros

SDSPI_DEFAULT_HOST
SDSPI_DEFAULT_DMA
SDSPI_HOST_DEFAULT()

Default sdmmc_host_t structure initializer for SD over SPI driver.

Uses SPI mode and max frequency set to 20MHz

‘slot’ should be set to an sdspi device initialized by sdspi_host_init_device().

SDSPI_SLOT_NO_CD

indicates that card detect line is not used

SDSPI_SLOT_NO_WP

indicates that write protect line is not used

SDSPI_SLOT_NO_INT

indicates that interrupt line is not used

SDSPI_DEVICE_CONFIG_DEFAULT()

Macro defining default configuration of SD SPI device.

Type Definitions

typedef int sdspi_dev_handle_t

Handle representing an SD SPI device.

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