LED

This utility provides a simple WS2812B RGB LED controller for Lichee-Jack.

It is implemented as a small shell wrapper around the shmled utility, which is written in C and acts as a shared memory writer for the ws2812b-gpio kernel driver.

shmled updates RGB frames in shared memory, while the kernel driver continuously reads and outputs them to the WS2812B LED.

Architecture Overview


Userspace
┌──────────────┐
│   LED script │
└──────┬───────┘
       │
┌──────▼───────┐
│    shmled    │  (shared memory writer)
└──────┬───────┘
       │ SHM
┌──────▼───────┐
│ ws2812-gpio  │  (kernel driver)
└──────┬───────┘
       │ GPIO
┌──────▼───────┐
│   WS2812B    │
└──────────────┘

LED Wrapper Script

The LED script ensures that only one instance of shmled is running.

When invoked, it:

Checks for an existing shmled process
Terminates it if found
Starts a new shmled instance with the given arguments


if pgrep -f shmled; then
    pkill shmled > /dev/null 2>&1
fi
 
shmled "$@" &

This makes it convenient to switch LED modes without manually managing processes.

Usage


root@licheejack:~# shmled -h
shmLED - Shared memory RGB LED writer for Lichee-Jack WS2812-GPIO Driver
 
Usage: shmled -c #RRGGBB -i <rgb bin file input> [-l -i|-b|-d|-r] [-s µs]
 
-c :    #RRGGBB, rgb hex code
-i :    <input.bin>, rgb bin file input, format: \xRR\xGG\xBB ...
 
-l :    loop mode:
    -b :    blink
    -d :    fade
    -r :    rainbow
    -i :    same as rgb file input, but loop mode
 
-s :    delay µs per frame
-h :    show this help
 
Version 0.0.1-licheejack By KaliAssistant
Github: https://github.com/KaliAssistant/Lichee-Jack-utils.git

Basic Examples

Set a Static Color

Set LED to solid red:


LED -c #FF0000

Set LED to green:


LED -c #00FF00

Blink Mode

Blink blue LED:


LED -c #0000FF -l -b -s 500000

Fade Mode

Fade smoothly between colors:


LED -c #FF0000 -l -d -s 20000

Rainbow Mode

Run built-in rainbow animation:


LED -l -r -s 30000

RGB Binary File Playback

You can generate custom RGB animations using a binary RGB file.

RGB Binary Format

Each frame consists of 3 bytes:


\xRR \xGG \xBB

Frames are played sequentially.

Generate a Simple RGB Pattern


printf "\xFF\x00\x00\xFF\x00\x00\xFF\x00\x00\x00\x00\xFF\x00\x00\xFF\x00\x00\xFF" > led.bin

This creates a pattern like:

Red
Red
Red
Blue
Blue
Blue
Red
Red
…

Play the RGB File


LED -l -i ./led.bin -s 50000

The LED will loop through the frames with a 50 ms delay, producing a playful blinking effect (“cop cop”).

Notes

Delay (-s) is specified in microseconds
Only one shmled instance should run at a time
Designed for single WS2812B LED by default
Shared memory allows extremely low-latency updates

LED