esp32_sdio_example

# Example of flashing through SDIO

## Overview

This example demonstrates how to flash an Espressif MCU (target) with SDIO download support from another MCU (host) using the `esp_serial_flasher`. In this case, another Espressif MCU is used as the host. Binaries to be flashed from the host MCU to the target Espressif SoC can be found in `binaries` folder and are converted into C-array during build process.

The following steps are performed in order to re-program the targets memory:

1. SDIO interface in slot 1 through which the binary will be transferred is initialized.
2. The host puts the slave device into joint download mode and tries to connect by calling `esp_loader_connect()`.
3. The binary file is opened and its size is acquired, as it has to be known before flashing.
4. Then `esp_loader_flash_start()` is called to enter the flashing mode and erase the amount of memory to be flashed.
5. `esp_loader_flash_write()` function is called repeatedly until the whole binary image is transferred.

## Hardware Required

* Two development boards, one with an Espressif SoC with an SDMMC peripheral (only ESP32-P4 is supported for now) and one Espressif SoC with SDIO download support (only ESP32-C6 is supported as the target MCU for now).

* One or two USB cables for power supply and programming.

> **Note:** Please check if your board has [possible issues](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/sd_pullup_requirements.html) regarding SDIO requirements.

## Hardware Connection

Table below shows connection between two Espressif MCUs.

| Host (ESP32-P4) | Target        |
|:---------------:|:-------------:|
|    IO_54        |    RESET      |
|    IO_4         |    BOOT       |
|    IO_14        |    D0         |
|    IO_15        |    D1         |
|    IO_16        |    D2         |
|    IO_17        |    D3         |
|    IO_18        |    CLK        |
|    IO_19        |    CMD        |
|    IO_5         |    UART0_RX   |
|    IO_6         |    UART0_TX   |

You can find the target SDIO pins for each target [here](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/sdio_slave.html).

SDIO pins CMD and DAT0-3 must be pulled up with adequate values, please take a look at the [SD Pull-up Requirements](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/sd_pullup_requirements.html) for more info.

> **Note:** For the ESP32 used as a reference, it is not possible to reassign SDIO pins, due to GPIO matrix limitations

## Build and Flash

To run the example, type the following command:

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

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

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

## Configuration

For details about available configuration options, please refer to the top level [README.md](../../README.md).
Compile definitions can be specified in the command line when running `idf.py`, for example:

```bash
idf.py build -DMD5_ENABLED=1
```

Binaries to be flashed are placed in a separate folder (binaries.c) for each possible target and converted to C-array. Without explicitly enabling MD5 check, flash integrity verification is disabled by default.

## Example output

Here is the example's console output:

```
Connected to target
I (1866) sdio_ram_loader: Loading bootloader...
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Flash verified
I (2226) sdio_ram_loader: Loading partition table...
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Flash verified
I (2276) sdio_ram_loader: Loading app...
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Flash verified
I (2906) sdio_ram_loader: Done!
I (3506) sdio_ram_loader: ********************************************
I (3506) sdio_ram_loader: *** Logs below are print from slave .... ***
I (3506) sdio_ram_loader: ********************************************
Hello world!
...
```