Module: UART

Defined in:
lib/uart.rb

Constant Summary collapse

VERSION =
'1.0.0'

Class Method Summary collapse

Class Method Details

.data_bits(t, val) ⇒ Object


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# File 'lib/uart.rb', line 67

def data_bits t, val
  t.cflag &= ~Termios::CSIZE               # clear previous values
  t.cflag |= Termios.const_get("CS#{val}") # Set the data bits
  t
end

.open(filename, speed = 9600, mode = '8N1') ⇒ Object

Open a UART as a file.

For example, we have a serial connection on `/dev/tty.usbserial-00000000'. It's speed is 9600, 8 data bits, 1 stop bit, and no parity:

serial = UART.open '/dev/tty.usbserial-00000000', 9600, '8N1'
serial.write 'whatever'

A speed of 9600, 8 data bits, no parity, and 1 stop bit is default, so we can reduce the code to this:

serial = UART.open '/dev/tty.usbserial-00000000'
serial.write 'whatever'

Finally, we can give a block and the file will be automatically closed for us like this:

UART.open '/dev/tty.usbserial-00000000' do |serial|
  serial.write 'whatever'
end

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# File 'lib/uart.rb', line 28

def open filename, speed = 9600, mode = '8N1'
  f = File.open filename, File::RDWR|Fcntl::O_NOCTTY|Fcntl::O_NDELAY
  f.binmode
  f.sync = true

  # enable blocking reads, otherwise read timeout won't work
  f.fcntl Fcntl::F_SETFL, f.fcntl(Fcntl::F_GETFL, 0) & ~Fcntl::O_NONBLOCK

  t = Termios.tcgetattr f
  t.iflag = 0
  t.oflag = 0
  t.lflag = 0

  if mode =~ /^(\d)(\w)(\d)$/
    t = data_bits    t, $1.to_i
    t = stop_bits    t, $3.to_i
    t = parity       t, { 'N' => :none, 'E' => :even, 'O' => :odd }[$2]
    t = speed        t, speed
    t = read_timeout t, 5
    t = reading      t
  else
    raise ArgumentError, "Invalid format for mode"
  end

  Termios.tcsetattr f, Termios::TCSANOW, t
  Termios.tcflush f, Termios::TCIOFLUSH

  if block_given?
    begin
      yield f
    ensure
      f.close
    end
  else
    f
  end
end

.parity(t, val) ⇒ Object


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# File 'lib/uart.rb', line 85

def parity t, val
  case val
  when :none
    t.cflag &= ~Termios::PARENB
  when :even
    t.cflag |= Termios::PARENB  # Enable parity
    t.cflag &= ~Termios::PARODD # Make it not odd
  when :odd
    t.cflag |= Termios::PARENB  # Enable parity
    t.cflag |= Termios::PARODD  # Make it odd
  else
    raise
  end
  t
end

.read_timeout(t, val) ⇒ Object


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# File 'lib/uart.rb', line 109

def read_timeout t, val
  t.cc[Termios::VTIME] = val
  t.cc[Termios::VMIN] = 0
  t
end

.reading(t) ⇒ Object


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# File 'lib/uart.rb', line 116

def reading t
  t.cflag |= Termios::CLOCAL | Termios::CREAD
  t
end

.speed(t, speed) ⇒ Object


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# File 'lib/uart.rb', line 102

def speed t, speed
  t.ispeed = Termios.const_get("B#{speed}")
  t.ospeed = Termios.const_get("B#{speed}")
  t
end

.stop_bits(t, val) ⇒ Object


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# File 'lib/uart.rb', line 74

def stop_bits t, val
  case val
  when 1 then t.cflag &= ~Termios::CSTOPB
  when 2 then t.cflag |= Termios::CSTOPB
  else
    raise
  end
  t
end