esp-idf/examples/storage/sd_card/sdspi/README.md

| Supported Targets | ESP32 | ESP32-S2 | ESP32-S3 | ESP32-C3 |
| ----------------- | ----- | -------- | -------- | -------- |

# SD Card example (SDSPI)

(See the README.md file in the upper level 'examples' directory for more information about examples.)

This example demonstrates how to use an SD card with an ESP device over an SPI interface. Example does the following steps:

1. Use an "all-in-one" `esp_vfs_fat_sdspi_mount` function to:
    - initialize SDSPI peripheral,
    - probe and initialize the card connected to SPI bus (DMA channel 1, MOSI, MISO and CLK lines, chip-specific SPI host id),
    - mount FAT filesystem using FATFS library (and format card, if the filesystem cannot be mounted),
    - register FAT filesystem in VFS, enabling C standard library and POSIX functions to be used.
2. Print information about the card, such as name, type, capacity, and maximum supported frequency.
3. Create a file using `fopen` and write to it using `fprintf`.
4. Rename the file. Before renaming, check if destination file already exists using `stat` function, and remove it using `unlink` function.
5. Open renamed file for reading, read back the line, and print it to the terminal.

This example support SD (SDSC, SDHC, SDXC) cards.

## Hardware

This example requires a development board with an SD card socket and and SD card.

Although it is possible to connect an SD card breakout adapter, keep in mind that connections using breakout cables are often unreliable and have poor signal integrity. You may need to use lower clock frequency when working with SD card breakout adapters.

It is recommended to get familiar with [the document about pullup requirements](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/sd_pullup_requirements.html) to understand Pullup/down resistor support and compatibility of various ESP modules and development boards.

### Pin assignments

The GPIO pin numbers used to connect an SD card can be customized. This can be done in two ways:

1. Using menuconfig: Run `idf.py menuconfig` in the project directory and open "SD SPI Example Configuration" menu.
2. In the source code: See the initialization of ``spi_bus_config_t`` and ``sdspi_device_config_t`` structures in the example code.

This example doesn't utilize card detect (CD) and write protect (WP) signals from SD card slot.

The table below shows the default pin assignments.

SD card pin | SPI pin | ESP32 pin     | ESP32-S2, ESP32-S3 | ESP32-C3 and other chips  |  Notes
------------|---------|---------------|--------------------|---------------------------|-------------
 D0         | MISO    | GPIO2         | GPIO37             | GPIO6                     |
 D3         | CS      | GPIO13 (MTCK) | GPIO34             | GPIO1                     |
 CLK        | SCK     | GPIO14 (MTMS) | GPIO36             | GPIO5                     |
 CMD        | MOSI    | GPIO15 (MTDO) | GPIO35             | GPIO4                     |  10k pullup


#### ESP32 related notes

With the default pin assignments, this example runs on ESP-WROVER-KIT boards without any extra modifications required. Only the SD card needs to be inserted into the slot.

For other development boards, adjust the pin assignments as explained above.

Some boards require specific manipulation to enable UART Download mode (GPIO2 low) - eg ESP32-Azure IoT Kit needs KEY_IO0 pressed down for the time of firmware flashing operation (sets IO0 and IO2 low). See troubleshooting section for more details

#### ESP32-S2 and ESP32-S3 related notes

With the default pin assignments, this example is compatible ESP32-S2-USB-OTG and ESP32-S3-USB-OTG development boards.

For other development boards, adjust the pin assignments as explained above.

#### Notes for ESP32-C3 and other chips

Espressif doesn't offer development boards with an SD card slot for these chips. Please check the pin assignments and adjust them for your board if necessary. The process to change pin assignments is described above.

### Build and flash

Build the project and flash it to the board, then run monitor tool to view serial output:

```
idf.py -p PORT flash monitor
```

(Replace PORT with serial port name.)

(To exit the serial monitor, type ``Ctrl-]``.)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.


## Example output

Here is an example console output. In this case a 64GB SDHC card was connected, and `EXAMPLE_FORMAT_IF_MOUNT_FAILED` menuconfig option enabled. Card was unformatted, so the initial mount has failed. Card was then partitioned, formatted, and mounted again.

```
I (336) example: Initializing SD card
I (336) example: Using SPI peripheral
I (336) gpio: GPIO[13]| InputEn: 0| OutputEn: 1| OpenDrain: 0| Pullup: 0| Pulldown: 0| Intr:0
W (596) vfs_fat_sdmmc: failed to mount card (13)
W (596) vfs_fat_sdmmc: partitioning card
W (596) vfs_fat_sdmmc: formatting card, allocation unit size=16384
W (7386) vfs_fat_sdmmc: mounting again
Name: XA0E5
Type: SDHC/SDXC
Speed: 20 MHz
Size: 61068MB
I (7386) example: Opening file /sdcard/hello.txt
I (7396) example: File written
I (7396) example: Renaming file /sdcard/hello.txt to /sdcard/foo.txt
I (7396) example: Reading file /sdcard/foo.txt
I (7396) example: Read from file: 'Hello XA0E5!'
I (7396) example: Card unmounted
```

## Troubleshooting

### Failure to mount filesystem

> The following error message is printed: `example: Failed to mount filesystem. If you want the card to be formatted, set the CONFIG_EXAMPLE_FORMAT_IF_MOUNT_FAILED menuconfig option.`

The example will be able to mount only cards formatted using FAT32 filesystem. If the card is formatted as exFAT or some other filesystem, you have an option to format it in the example code. Enable the `CONFIG_EXAMPLE_FORMAT_IF_MOUNT_FAILED` menuconfig option, then build and flash the example.


### Unable to flash the example, or serial port not available (ESP32 only)

> After the first successful flashing of the example firmware, it is not possible to flash again. Download mode not activated when running `idf.py flash` or the board's serial port disappears completely.

Some ESP32 boards require specific handling to activate the download mode after a system reset, due to GPIO2 pin now being used as both SDSPI (MISO) and an active-low bootstrapping signal for entering download mode. For instance, the ESP32-Azure IoT Kit requires KEY_IO0 button to remain pressed during whole firmware flashing operation, as it sets both GPIO0 and GPIO2 signals low.

Check you board documentation/schematics for appropriate procedure.

An attempt to download a new firmware under this conditions may also result in the board's serial port disappearing from your PC device list - rebooting your computer should fix the issue. After your device is back, use

`esptool --port PORT --before no_reset --baud 115200 --chip esp32 erase_flash`

to erase your board's flash, then flash the firmware again.