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Stdio Input

LVGL operations are typically touchscreens, but keyboard input is also possible. Here, we explain how to simulate keyboard input from Stdio.

Wiring

The TFT LCD uses ST7789. The breadboard wiring image is as follows:

circuit-st7789-uart.png

Building and Flashing the Program

Create a new Pico SDK project named lvgl-stdio.

Create Pico SDK Project
  1. In VSCode, run >Raspberry Pi Pico: New Pico Project in the command palette.

  2. In the dialog below, select C/C++. new-project-dialog

  3. Create a project with the following settings:

    • Name ... Enter the project name.
    • Board type ... Select your board type.
    • Location ... Select the parent directory where the project directory will be created.
    • Stdio support ... Leave Console over USB unchecked when you use LABOPlatform or other USB features because they conflict with each other. You can enable it by editing the CMakeLists.txt file later.
    • Code generation options ... Check Generate C++ code.

new-project

Open Existing Pico SDK Project

Open the project folder in VSCode using one of the following methods:

  • In a command prompt, change the current directory to the project folder and execute code ..

  • In a Explorer, choose the project folder, push Alt+D to focus the address bar, and execute code ..

    vscode-from-explorer

If the folder is already prepared as a Pico SDK project, just proceed with editing and building the project.

If not, you will see the following message at the bottom right corner of VSCode.

do-you-want-to-import

Click Yes and you will see the following window.

import-project

Click Import and the project will be prepared as a Pico SDK project.

When the Do you want to import this project as Raspberry Pi Pico project? message disappears before you click Yes, you can reveal it by clicking the icon notify-icon at the bottom right corner of VSCode.

Clone the pico-jxglib repository from GitHub so the direcory structure looks like this:

├── pico-jxglib/
└── lvgl-stdio/
    ├── CMakeLists.txt
    ├── lvgl-stdio.cpp
    └── ...
Clone the Repository

Change the current directory to the parent directory where you want to clone the pico-jxglib repository and run the following commands:

$ git clone https://github.com/ypsitau/pico-jxglib.git
$ cd pico-jxglib
$ git submodule update --init --recursive

pico-jxglib is updated almost daily. If you've already cloned it, run the following command in the pico-jxglib directory to get the latest version:

$ git pull

A directory from a Git repository can safely be moved to another location even after cloning.

Add the following lines to the end of CMakeLists.txt:

CMakeLists.txt
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target_link_libraries(lvgl-stdio
    jxglib_LVGL lvgl_examples
    jxglib_Display_ST7789)
add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../pico-jxglib pico-jxglib)
jxglib_configure_LVGL(lvgl-stdio LV_FONT_MONTSERRAT_14)

Edit lvgl-stdio.cpp as follows:

lvgl-stdio.cpp
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#include <stdio.h>
#include <examples/lv_examples.h>
#include "pico/stdlib.h"
#include "jxglib/Stdio.h"
#include "jxglib/Display/ST7789.h"
#include "jxglib/LVGL.h"

using namespace jxglib;

int main()
{
    ::stdio_init_all();
    ::spi_init(spi1, 125 * 1000 * 1000);
    GPIO14.set_function_SPI1_SCK();
    GPIO15.set_function_SPI1_TX();
    Display::ST7789 display(spi1, 240, 320, {RST: GPIO10, DC: GPIO11, CS: GPIO12, BL: GPIO13});
    display.Initialize(Display::Dir::Rotate90);
    LVGL::Initialize();
    LVGL::Adapter lvglAdapter;
    lvglAdapter.EnableDoubleBuff().AttachDisplay(display).AttachKeyboard(Stdio::GetKeyboard());
    ::lv_example_keyboard_1();
    for (;;) {
        ::sleep_ms(5);
        ::lv_timer_handler();
    }
}

Build and flash the program to the board.

Build and Flash

The simplest way to build and flash the program is to use the UF2 file generated by the build process. Pico board, a USB cable, and a computer are all you need to get started. Here are the steps to build and flash the program:

  1. Pressing F7 on VSCode will build the project. If this is the first time you build the project, you will see the dialog shown below. Select Pico Using compilers: ... and the build process will start.

    select-a-kit

  2. After building, you can find the generated UF2 file in the build directory.

  3. Connect your Pico to the computer using a USB cable while holding the BOOTSEL button, and it will appear as a mass storage device. Copy the generated UF2 file to this device to flash it. No need to mind the destination directory, just copy it to the root directory of the device.

If you have a debug probe like this, you can also flash the program using OpenOCD and GDB. This is the recommended method for development, as it allows you to debug the program while running it on the board!

Running the Program

PgUp and PgDn move the focus. Enter clicks the focused widget.