SD SPI Host Driver
Overview
The SD SPI host driver allows communication with one or more SD cards using the SPI Master driver, which utilizes the SPI host. Each card is accessed through an SD SPI device, represented by an SD SPI handle sdspi_dev_handle_t
, which returns when the device is attached to an SPI bus by calling sdspi_host_init_device()
. It is important to note that the SPI bus should be initialized beforehand 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 that accesses 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 an SDMMC host driver is used (see SDMMC Host Driver) to access the card in SD 1-bit/4-bit mode, higher throughput can be reached while requiring routing the signals through their dedicated IO_MUX pins only.
With the help of SPI Master Driver the SD SPI host 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 the structure sdspi_device_config_t
, which is used to initialize an SD SPI device. This macro will also fill in the default pin mappings, which are the same as the pin mappings of the 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 the SDSPI_HOST_DEFAULT
macro to initialize the sdmmc_host_t
structure, which is used to store the state and configurations of the upper layer (SD/SDIO/MMC driver). Modify the slot
parameter of the structure to the SD SPI device SD 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 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 Cards and Other SPI Devices.
API Reference
Header File
This header file can be included with:
#include "driver/sdspi_host.h"
This header file is a part of the API provided by the
esp_driver_sdspi
component. To declare that your component depends onesp_driver_sdspi
, add the following to your CMakeLists.txt:REQUIRES esp_driver_sdspi
or
PRIV_REQUIRES esp_driver_sdspi
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_get_real_freq(sdspi_dev_handle_t handle, int *real_freq_khz)
Calculate working frequency for specific device.
- Parameters
handle -- SDSPI device handle
real_freq_khz -- [out] output parameter to hold the calculated frequency (in kHz)
- Returns
ESP_ERR_INVALID_ARG :
handle
is NULL or invalid orreal_freq_khz
parameter is NULLESP_OK : Success
-
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.
-
bool gpio_wp_polarity
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.
-
uint16_t duty_cycle_pos
Duty cycle of positive clock, in 1/256th increments (128 = 50%/50% duty). Setting this to 0 (=not setting it) is equivalent to setting this to 128.
-
spi_host_device_t host_id
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_CS
indicates that card select line is not used
-
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_IO_ACTIVE_LOW
-
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.