Class: LGPIO::OneWire

Inherits:
Object
  • Object
show all
Defined in:
lib/lgpio/one_wire.rb

Constant Summary collapse

READ_POWER_SUPPLY =

Constants

0xB4
CONVERT_T = 
0x44
SEARCH_ROM = 
0xF0
READ_ROM = 
0x33
SKIP_ROM = 
0xCC
MATCH_ROM = 
0x55
ALARM_SEARCH = 
0xEC
READ_SCRATCH = 
0xBE
WRITE_SCRATCH = 
0x4E
COPY_SCRATCH = 
0x48
RECALL_EEPROM = 
0xB8

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(handle, gpio) ⇒ OneWire

Returns a new instance of OneWire.



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# File 'lib/lgpio/one_wire.rb', line 18

def initialize(handle, gpio)
  @handle = handle
  @gpio   = gpio
  @found_addresses = []
  LGPIO.gpio_claim_output(handle, gpio, LGPIO::SET_OPEN_DRAIN | LGPIO::SET_PULL_UP, LGPIO::HIGH)
end

Instance Attribute Details

#found_addresses ⇒ Object (readonly)

Returns the value of attribute found_addresses.



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# File 'lib/lgpio/one_wire.rb', line 16

def found_addresses
  @found_addresses
end

#gpio ⇒ Object (readonly)

Returns the value of attribute gpio.



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# File 'lib/lgpio/one_wire.rb', line 16

def gpio
  @gpio
end

#handle ⇒ Object (readonly)

Returns the value of attribute handle.



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# File 'lib/lgpio/one_wire.rb', line 16

def handle
  @handle
end

Class Method Details

.address_to_bytes(address) ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 167

def self.address_to_bytes(address)
  [address].pack('Q<').split("").map(&:ord)
end

.calculate_crc(data) ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 148

def self.calculate_crc(data)
  if data.class == Integer
    bytes = address_to_bytes(data)
  else
    bytes = data
  end

  crc = 0b00000000
  bytes.take(bytes.length - 1).each do |byte|
    for bit in (0..7)
      xor = byte[bit] ^ crc[0]
      crc = crc ^ ((xor * (2 ** 3)) | (xor * (2 ** 4)))
      crc = crc >> 1
      crc = crc | (xor * (2 ** 7))
    end
  end
  [crc, bytes.last]
end

.crc(data) ⇒ Object

CRC Class Methods



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# File 'lib/lgpio/one_wire.rb', line 143

def self.crc(data)
  calculated, received = self.calculate_crc(data)
  calculated == received
end

Instance Method Details

#parse_search_result(result) ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 116

def parse_search_result(result)
  address, complement = split_search_result(result)

  raise "OneWire device not connected, or disconnected during search" if (address & complement) > 0
  raise "CRC error during OneWire search" unless OneWire.crc(address)

  # Gives 0 at every discrepancy we didn't write 1 for on this pass.
  new_discrepancies = address ^ complement

  high_discrepancy = -1
  (0..63).each { |i| high_discrepancy = i if new_discrepancies[i] == 0 }

  [address, high_discrepancy]
end

#read(byte_count) ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 30

def read(byte_count)
  read_bytes = []
  byte_count.times do
    byte = 0b00000000
    8.times { |i| byte |= LGPIO.one_wire_bit_read(handle, gpio) << i }
    read_bytes << byte
  end
  read_bytes
end

#reset ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 25

def reset
  # LGPIO.one_wire_reset returns 0 if device present on bus.
  return (LGPIO.one_wire_reset(handle, gpio) == 0)
end

#search ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 48

def search
  branch_mask      = 0
  high_discrepancy = 0

  loop do
    reset
    write [SEARCH_ROM]
    result = search_pass(branch_mask)

    address, high_discrepancy = parse_search_result(result)
    @found_addresses << address

    # No unsearched discrepancies left.
    break if high_discrepancy == -1

    # Force highest new discrepancy to be a 1 on the next search.
    # i.e. Go as deep as possible into each branch found then back out.
    #
    branch_mask = branch_mask | (2 ** high_discrepancy)

    # Clear bits above high_discrepancy so we don't repeat branches.
    # When high_discrepancy < MSB of branch_mask, this moves us
    # one node out, closer to the root, and finishing the search.
    #
    unset_mask = 0xFFFFFFFFFFFFFFFF >> (63 - high_discrepancy)
    branch_mask = branch_mask & unset_mask
  end
end

#search_pass(mask) ⇒ Object

Read a single 64-bit address and complement from the bus.



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# File 'lib/lgpio/one_wire.rb', line 78

def search_pass(mask)
  bytes = []

  8.times do |i|
    addr = 0
    comp = 0
    8.times do |j|
      addr |= LGPIO.one_wire_bit_read(handle, gpio) << j
      comp |= LGPIO.one_wire_bit_read(handle, gpio) << j

      # A set (1) mask bit means we're searching a branch with that bit set.
      # Force it to be 1 on this pass. Write 1 to both the bus and address bit.
      #
      # Don't change the complement bit from 0, Even if the bus said 0/0,
      # send back 1/0, hiding known discrepancies, only sending new ones.
      #
      # Mask is a 64-bit number, not byte array.
      if ((mask >> (i*8 + j)) & 0b1) == 1
        LGPIO.one_wire_bit_write(handle, gpio, 1)
        addr |= 1 << j

      # Whether there was no "1-branch" marked for this bit, or there is no
      # discrepancy at all, just echo address bit to the bus. We will
      # compare addr/comp to find discrepancies for future passes.
      else
        LGPIO.one_wire_bit_write(handle, gpio, (addr >> j) & 0b1)
      end
    end
    bytes << addr
    bytes << comp
  end

  # 16 bytes, address and complement bytes interleaved LSByteFIRST.
  # DON'T CHANGE! #split_search_result deals with it. denko uses #search_pass
  # directly on Linux, but MCUs send it this format to save RAM. Always match it.
  return bytes
end

#split_search_result(data) ⇒ Object

Convert interleaved address/complement bytes to 64-bit numbers.



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# File 'lib/lgpio/one_wire.rb', line 132

def split_search_result(data)
  address    = 0
  complement = 0
  data.reverse.each_slice(2) do |comp_byte, addr_byte|
    address    = (address << 8)    | addr_byte
    complement = (complement << 8) | comp_byte
  end
  [address, complement]
end

#write(byte_array, parasite: nil) ⇒ Object 



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# File 'lib/lgpio/one_wire.rb', line 40

def write(byte_array, parasite: nil)
  byte_array.each do |byte|
    8.times { |i| LGPIO.one_wire_bit_write(handle, gpio, (byte >> i) & 0b1) }
  end
  # Drive bus high to feed parasite capacitor after write.
  LGPIO.gpio_write(handle, gpio, LGPIO::HIGH) if parasite
end