Module: MmGPS

Defined in:
lib/mm_gps/mm_gps_module.rb,
lib/mm_gps.rb,
lib/mm_gps/version.rb,
lib/mm_gps/mm_gps_beacon.rb,
lib/mm_gps/mm_gps_buffer.rb,
ext/mm_gps/mm_gps.c

Overview

Manage connection and data decoding with a MarvelMind beacon or hedgehog.

Defined Under Namespace

Classes: Beacon, Buffer

Constant Summary collapse

VERSION = 
"0.2.1"

Class Method Summary collapse

Class Method Details

.append_crc16(buf) ⇒ String

Appends a CRC16 checksum to a string

Parameters:

  • buf (String) —

    the starting string

Returns:

  • (String) —

    the original string plus its CRC16



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# File 'ext/mm_gps/mm_gps.c', line 52

static VALUE mm_gps_add_CRC16(VALUE klass, VALUE str)
{
  union {
    ushort u;
    char   s[2];
  } crc;
  
  Check_Type(str, T_STRING);
  crc.u = CRC16(RSTRING_PTR(str), RSTRING_LEN(str));  
  return rb_str_buf_cat(str, crc.s, 2);
}

.crc16(buf) ⇒ Fixnum

Calculate CRC16 checksum of a string

Parameters:

  • buf (String) —

    the string to be checksummed

Returns:

  • (Fixnum) —

    the CRC16 value



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# File 'ext/mm_gps/mm_gps.c', line 40

static VALUE mm_gps_CRC16(VALUE klass, VALUE str)
{
  Check_Type(str, T_STRING);
  return rb_fix_new(CRC16(RSTRING_PTR(str), RSTRING_LEN(str)));
}

.hexify(buf) ⇒ String

Returns a HEX description of a binary buffer

Parameters:

  • buf (String) —

    the input buffer

Returns:

  • (String) —

    the HEX description



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# File 'lib/mm_gps/mm_gps_module.rb', line 39

def self.hexify(buf)
  len = buf.length
  return (("%02X " * len) % buf.unpack("C#{len}")).chop
rescue NoMethodError
  return '--'
end

.parse_packet(buf) ⇒ Hash|Array

Parse the given buffer according to the MarvelMind protocol. See www.marvelmind.com/pics/marvelmind_beacon_interfaces_v2016_03_07a.pdf

Parameters:

  • buf (String) —

    the String buffer to be parsed

Returns:

  • (Hash|Array) —

    if the system is running, return a Hash with timestamp, coordinates, and error code (data code 0x0001). Otherwise returns an Array of Hashes for beacons status (data code 0x0002).



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# File 'lib/mm_gps/mm_gps_module.rb', line 52

def self.parse_packet(buf)
  unless valid_crc16?(buf) then
    raise MmGPSError.new("Invalid CRC", {reason: :nocrc, packet:buf, crc:("%04X" % crc16(buf[0...-2]))}) 
  end
  header = buf[0..5].unpack('CCS<C')
  if header[2] == 1 then # Regular GPS Data
    result = {}
    payload = buf[5...16].unpack('L<s<3C')
    result = %I(ts x y z f).zip(payload).to_h
    result[:ts] /= 64.0
    %I(x y z).each {|k| result[k] /= 100.0}
  elsif header[2] == 2 then # Frozen
    len = buf[5].unpack('C')[0]
    result = []
    len.times do |i|
      offset = 6 + i * 8
      payload = buf[offset...(offset + 8)].unpack('Cs<3C')
      result << %I(address x y z reserved).zip(payload).to_h
      %I(x y z).each {|k| result.last[k] /= 100.0}
    end
  else
    unless valid_crc16?(buf) then
      raise MmGPSError.new("Unexpected packet type #{header[2]}",
        {reason: :notype, packet:buf, crc:("%04X" % crc16(buf[0...-2])), type:header[2]}) 
    end
  end
  return result
end

.valid_crc16?(str) ⇒ Bool

Checks a sbuffer for valid CRC16.

Parameters:

  • str (String) —

    the buffer to be checked

Returns:

  • (Bool) —

    true if the buffer is self-consistent



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# File 'lib/mm_gps/mm_gps_module.rb', line 31

def self.valid_crc16?(str)
  crc16(str) == 0
end