lvglterm LVGL Terminal for NuttShell (NSH)

LVGL application that runs an interactive NuttShell (NSH) on the display. NSH is started with its standard streams redirected through pipes, its output is rendered in an LVGL text area, and the input comes from either a touchscreen or a keyboard, selected at build time.

The shared code lives in lvglterm.c (NSH startup, output rendering, main loop); lvglterm_touch.c and lvglterm_kbd.c implement the input variants.

Input variants

The input source is chosen with the LVGL Terminal input source Kconfig choice (only one is built at a time).

On-screen keyboard (touch)

CONFIG_EXAMPLES_LVGLTERM_INPUT_TOUCH (default). An LVGL keyboard widget operated by touch; a command line is typed and submitted with Enter. Suits touchscreen boards and keeps the original behaviour.

LVGL Terminal with the on-screen touch keyboard

On-screen keyboard (touch) variant

Physical keyboard

CONFIG_EXAMPLES_LVGLTERM_INPUT_KBD. Keys are read from a keyboard registered with keyboard_register() and streamed to the shell; the output fills the whole screen. The Up and Down cursor keys scroll the output. Any keyboard works, and the terminal does not need to know which kind it is: USB HID, a matrix, the simulator, virtio.

LVGL Terminal driven by a matrix keyboard

Physical keyboard variant, driven by a matrix keyboard

LVGL Terminal driven by a USB HID keyboard

The same variant, driven by a USB HID keyboard

The keyboard defaults to CONFIG_EXAMPLES_LVGLTERM_KBD_DEV and can be overridden at run time by passing the path as the first argument (lvglterm /dev/kbd1) when more than one keyboard is present. Note that the USB HID driver names its devices /dev/kbda onwards, since they come and go as keyboards are plugged in, while the option defaults to /dev/kbd0.

The terminal reads struct keyboard_event_s events unless the kernel was built with CONFIG_INPUT_KEYBOARD_BYTESTREAM, in which case it reads the byte stream that the keyboard codec defines. That is a property of the build rather than of the hardware, so it is not something to configure here.

Driving the terminal without a keyboard

Because the terminal reads a keyboard device and does not care which one, it can be driven from the serial console with nothing plugged in. Enable CONFIG_UINPUT_KEYBOARD, which registers a virtual keyboard on /dev/ukeyboard, and CONFIG_SYSTEM_KBD, which injects into it:

nsh> lvglterm /dev/ukeyboard &
nsh> kbd -i /dev/ukeyboard

Everything typed on the console appears on the display from that point on. Forwarding a real keyboard into the same virtual one lets both drive the terminal at once, which it cannot do by itself since it opens a single device:

nsh> kbd -i /dev/ukeyboard /dev/kbda &

Raise CONFIG_UINPUT_KEYBOARD_BUFNUMBER when doing this. It counts events rather than keys, so the default of eight holds four keystrokes, and a console hands over a whole line at once.

Font

The monospaced terminal font is chosen with the LVGL Terminal font choice: CONFIG_EXAMPLES_LVGLTERM_FONT_UNSCII_16 (default), or the smaller CONFIG_EXAMPLES_LVGLTERM_FONT_UNSCII_8 for low-resolution displays where UNSCII 16 shows too few columns.

Configuration

  • CONFIG_LIBC_EXECFUNCS=y – posix_spawn() must be enabled.

  • CONFIG_PIPES=y – Pipes must be enabled.

  • CONFIG_SYSTEM_NSH=y – the NSH library must be enabled.

  • CONFIG_GRAPHICS_LVGL=y and CONFIG_LV_USE_NUTTX=y – LVGL with its NuttX integration.

  • A display (CONFIG_LV_USE_NUTTX_LCD or a framebuffer). Each input variant also needs its own driver: a touchscreen (CONFIG_LV_USE_NUTTX_TOUCHSCREEN) for the touch variant, or CONFIG_INPUT_KEYBOARD and a keyboard driver for the physical variant. CONFIG_LIBC_KBDCODEC is selected automatically when the build delivers the byte stream.

  • The selected font (CONFIG_LV_FONT_UNSCII_8 or CONFIG_LV_FONT_UNSCII_16) is enabled automatically by the font choice.

Reference: NuttX RTOS for PinePhone: LVGL Terminal for NSH Shell.