Keyboard

Wiring

Here is the breadboard wiring image:

When running the Pico as a USB device, you can power it from the USB connector, but when using it as a host, you need to supply 5V to VBUS (pin 40) from an external source. If you connect power to VSYS (pin 39), the diode for reverse current protection will prevent power from reaching USB VBUS, so be careful.

Building and Flashing the Program

Create a new Pico SDK project named usbhost-keyboard.

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++.

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.

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 ..

  

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.

Click Yes and you will see the following window.

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 at the bottom right corner of VSCode.

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

├── pico-jxglib/
└── usbhost-keyboard/
    ├── CMakeLists.txt
    ├── usbhost-keyboard.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:

target_link_libraries(usb-keyboard
    jxglib_USBHost)
add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../pico-jxglib pico-jxglib)
jxglib_configure_USBHost(usb-keyboard CFG_TUH_HID 1)

Enable UART or USB stdio as described below.

Enable UART and/or USB stdio

Find the following lines in CMakeLists.txt:

pico_enable_stdio_uart(your-project 0)
pico_enable_stdio_usb(your-project 0)

You can set the value to 1 to enable stdio or 0 to disable it.

• pico_enable_stdio_uart() enables UART stdio that uses GPIO0 (UART0 TX) and GPIO1 (UART0 RX).
• pico_enable_stdio_usb() enables USB stdio that uses the USB interface. Make sure to disable USB stdio when you use USB features because they conflict with each other.

Edit usbhost-keyboard.cpp as follows:

#include <stdio.h>
#include "pico/stdlib.h"
#include "jxglib/USBHost/HID.h"

using namespace jxglib;

int main()
{
    ::stdio_init_all();
    // Initialize the USB Host and Keyboard
    USBHost::Initialize();
    USBHost::Keyboard keyboard;
    for (;;) {
        KeyData keyData;
        if (keyboard.GetKeyDataNB(&keyData)) {
            char ch = keyData.GetChar();
            if (ch) {
                ::printf("Char:    '%c'\n", ch);
            } else {
                ::printf("KeyCode: 0x%02x (modifier: %03b)\n", keyData.GetKeyCode(), keyData.GetModifier());
            }
        }
        Tickable::Sleep(100);
    }
}

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.

   

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

Open a terminal emulator to connect it.

Setup Tera Term for stdio

Tera Term is available here.

From the menu bar, select [File] - [New Connection...] to open the dialog below:

Select the appropriate serial port for your Pico board and press Enter key in the terminal. When successfully connected, you will see a prompt in the terminal, which varies depending on the firmware.

A prompt will appear in the terminal like this:

>

About the Program

To use the USB host functionality in pico-jxglib, use the USBHost class.

Create a USBHost::Keyboard instance and use the following APIs to get keyboard information:

• Keyboard::IsPressed() — Checks if a specified key is pressed
• Keyboard::ScanKeyCode() — Returns the keycode of the pressed key
• Keyboard::ScanKeyData() — Returns the KeyData (keycode and character code) of the pressed key
• Keyboard::GetKeyCode() — While a key is pressed, repeats and returns the keycode; blocks if no key is pressed
• Keyboard::GetKeyCodeNB() — While a key is pressed, repeats and returns the keycode; returns false immediately if no key is pressed
• Keyboard::GetKeyData() — While a key is pressed, repeats and returns the KeyData; blocks if no key is pressed
• Keyboard::GetKeyDataNB() — While a key is pressed, repeats and returns the KeyData; returns false immediately if no key is pressed

The jxglib_configure_USBHost() function generates the tusb_config.h header file needed for building tinyusb. The argument CFG_TUH_HID specifies the maximum number of HID interfaces to connect.

Below is an example using Keyboard::IsPressed(). The LED lights up when the specified key is pressed.

The Tickable::Sleep() function is specified in milliseconds. This function runs the tinyusb and pico-jxglib tasks.

Below is an example using Keyboard::GetKeyCodeNB(). The LED blinks in response to the repeated key presses.