lighttroupe/luz-next

#
# DMX support, specifically targeting the "Enttec DMX USB Pro" device
#
#  https://en.wikipedia.org/wiki/DMX512
#
require 'serialport'

class DMX
    START_OF_MESSAGE = "\x7E"
    SEND_DMX_LABEL   = "\x06"    # ID of the message type we send, DMX channel values
    START_OF_DATA    = "\x00"
    END_OF_MESSAGE   = "\xE7"

    SERIAL_PORT_PARAMS = {
        'baud' => 115_200,
        'data_bits' => 8,
        'stop_bits' => 2,
        'parity' => SerialPort::NONE
    }

    #
    # Wikipedia says "A maximum-sized packet, which has 512 channels, takes
    # approximately 23 ms to send, corresponding to a max refresh rate of ~44 Hz.
    # For higher refresh rates, packets having fewer than 512 channels can be sent.
    #
    def initialize(path, channel_count)
        raise ArgumentError.new("channel_count must be between 25 and 512") if (channel_count < 25 or channel_count > 512)

        @path, @channel_count = path, channel_count

        @port = SerialPort.new(@path, SERIAL_PORT_PARAMS)

        # Allocate a buffer once, so we don't continually produce garbage
        @packet = "\0" * (@channel_count + 6)        # 6 bytes of START_OF_MESSAGE, etc.
        @clear_string = "\0" * @channel_count

        # Set the static values
        @packet[0] = START_OF_MESSAGE
        @packet[1] = SEND_DMX_LABEL
        payload_size = (@channel_count + 1)        # +1 is for the start code
        @packet[2] = (payload_size & 255).chr                    # LSB of size
        @packet[3] = ((payload_size >> 8) & 255).chr    # MSB of size
        @packet[4] = START_OF_DATA
        # @channel_count bytes of DMX channels
        @packet[4 + @channel_count + 1] = END_OF_MESSAGE

        @starting_channel = 1
    end

    def with_starting_channel(channel)
        return yield if channel == @starting_channel

        raise ArgumentError.new("channel out of range") if (channel < 1 or channel > @channel_count)
        old_starting_channel = @starting_channel
        @starting_channel = channel
        yield
        @starting_channel = old_starting_channel
    end

    def set(channel, value)
        channel_with_offset = channel + (@starting_channel - 1)
        raise ArgumentError.new("channel out of range") if (channel_with_offset < 1 or channel_with_offset > @channel_count)
        @packet[5 + channel_with_offset - 1] = value.to_i.chr
    end

    def get(channel)
        channel_with_offset = channel + (@starting_channel - 1)
        raise ArgumentError.new("channel out of range") if (channel_with_offset < 1 or channel_with_offset > @channel_count)
        @packet[5 + channel_with_offset - 1].ord
    end

    # Helper method
    def add(channel, value)
        set(channel, (get(channel) + value).clamp(0, 255))
    end

    def send
        begin
            @port.write(@packet)
        rescue Errno::EIO
            # ignore?
        rescue Exception => e
            puts "Exception writing to DMX serial port: #{e}"
        end
    end

    def clear
        @packet[5, @channel_count] = @clear_string
    end
end

#
# Example usage
#
=begin
    dmx = DMX.new('/dev/ttyUSB0', 256)
    v = 1
    loop {
        # Test values for a Chauvet Colorsplash JR
        dmx.set(1, 0)                                # reserved
        dmx.set(2, 255)                            # brightness
        dmx.add(3, v % 255)                    # R
        dmx.add(4, 0)                                # G
        dmx.add(5, 255 - (v % 255))    # B
        dmx.send
        v += 1
    }
=end