pi_pico_example

Raspberry Pi Pico Example

Overview

This example demonstrates how to flash an Espressif SoC (target) from a Raspberry Pi Pico Series MCU (host) using esp_serial_flasher. uart1 is dedicated for communication with the Espressif SoC, whereas, either uart0 or USB can be used for debug output.

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

1. Peripherals are initialized.
2. Host puts the slave device into boot mode and tries to connect by calling esp_loader_connect().
3. Then esp_loader_flash_start() is called to enter the flashing mode and erase the amount of memory to be flashed.
4. The esp_loader_flash_write() function is called repeatedly until the whole binary image is transferred.

In addition to the steps mentioned above, esp_loader_change_transmission_rate() is called after connection is established in order to increase the flashing speed. The bootloader is also capable of detecting the baud rate during connection phase, however, it is recommended to start at lower speed and then use dedicated command to increase the baud rate. This does not apply for the ESP8266, as its bootloader does not support this command, therefore, baud rate can only be changed before the connection phase in this case.

Hardware Required

• A Raspberry Pi Pico Board with 2MB of flash or more.
• A development board with an Espressif SoC (e.g. ESP-WROVER-KIT, ESP32-DevKitC, etc.).
• Jumper cables to connect the boards.
• One or two USB cables for power supply and programming.

Hardware Connection

This example uses the UART interface. For detailed interface information and general hardware considerations, see the Hardware Connections Guide.

Pi Pico-to-Espressif SoC Pin Assignment:

Pi Pico (host)	Espressif SoC (target)
18	BOOT
19	RESET
20	RX0
21	TX0

Prepare Target Firmware

Place the required target firmware binaries in the target-firmware/ directory. You can use your own binaries, build them from the esp-idf examples, or build them from the source in the test/target-example-src directory.

Required binaries:

• bootloader.bin - ESP bootloader binary
• partition-table.bin - Partition table configuration
• app.bin - Main application binary

To build from the example source:

cd test/target-example-src/hello-world-ESP32-src
idf.py set-target esp32s3  # Set target chip (esp32, esp32s3, esp32c3, etc.)
idf.py fullclean
idf.py -D SDKCONFIG_DEFAULTS=sdkconfig.defaults.flash reconfigure build

# Copy binaries to example
cp build/bootloader/bootloader.bin ../../pi_pico_example/target-firmware/
cp build/partition_table/partition-table.bin ../../pi_pico_example/target-firmware/
cp build/hello_world.bin ../../pi_pico_example/target-firmware/app.bin

Build and Flash

First, either export the SDK location in your shell:

export PICO_SDK_PATH=<sdk_location>

or set the PICO_SDK_FETCH_FROM_GIT CMake variable for the SDK to be pulled from GitHub.

Create and navigate to the example build directory:

mkdir build && cd build

Run CMake (with appropriate parameters) and build:

cmake .. && cmake --build .

Note

CMake 3.22 or later is required.

Binaries to be flashed are placed in the binaries.c file for each possible target and converted to C arrays. Flash integrity verification is enabled by default.

For more details regarding esp_serial_flasher configuration and Raspberry Pi Pico support, please refer to the top level README.md.

Finally, flash the board by connecting your Raspberry Pi Pico board to your PC, with the BOOTSEL button pressed and copy over the .uf2 file from the example build directory to the Mass Storage Device the Pico presents itself as.

To see the debug output, connect to the boards virtual com port with a serial monitor (e.g. using minicom):

minicom -b 115200 -o -D /dev/ttyACM0

Here is the example's console output:

Connected to target
Transmission rate changed changed
Loading bootloader...
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Loading partition table...
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Loading app...
Erasing flash (this may take a while)...
Start programming
Progress: 100 %
Finished programming
Done!