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#!/usr/bin/env ruby -w
# encoding: UTF-8
#
# = EPO_Downloader.rb -- PostRunner - Manage the data from your Garmin sport devices.
#
# Copyright (c) 2015 by Chris Schlaeger <cs@taskjuggler.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of version 2 of the GNU General Public License as
# published by the Free Software Foundation.
#
require 'uri'
require 'net/http'
module PostRunner
# This class can download the current set of Extended Prediction Orbit data
# for GPS satellites and store them in the EPO.BIN file format. Some Garmin
# devices pick up this file under GARMIN/GARMIN/REMOTESW/EPO.BIN.
class EPO_Downloader
@@URI = URI('http://omt.garmin.com/Rce/ProtobufApi/EphemerisService/GetEphemerisData')
# This is the payload of the POST request. It was taken from
# http://www.kluenter.de/garmin-ephemeris-files-and-linux/. It may contain
# a product ID or serial number.
@@POST_DATA = "\n-\n\aexpress\u0012\u0005de_DE\u001A\aWindows\"\u0012601 Service Pack 1\u0012\n\b\x8C\xB4\x93\xB8\u000E\u0012\u0000\u0018\u0000\u0018\u001C\"\u0000"
@@HEADER = {
'Garmin-Client-Name' => 'CoreService',
'Content-Type' => 'application/octet-stream',
'Content-Length' => '63'
}
# Create an EPO_Downloader object.
def initialize
@http = Net::HTTP.new(@@URI.host, @@URI.port)
@request = Net::HTTP::Post.new(@@URI.path, initheader = @@HEADER)
@request.body = @@POST_DATA
end
# Download the current EPO data from the Garmin server and write it into
# the specified output file.
# @param output_file [String] The name of the output file. Usually this is
# 'EPO.BIN'.
def download(output_file)
return false unless (epo = get_epo_from_server)
return false unless (epo = fix(epo))
return false unless check_epo_data(epo)
write_file(output_file, epo)
Log.info "Extended Prediction Orbit (EPO) data has been downloaded " +
"from Garmin site."
true
end
private
def get_epo_from_server
res = @http.request(@request)
if res.code.to_i != 200
Log.error "Extended Orbit Prediction (EPO) data download failed: #{res}"
return nil
end
res.body
end
# The downloaded data contains Extended Prediction Orbit data for 6 hour
# windows for 7 days. Each EPO set is 2307 bytes long, but the first 3
# bytes must be removed for the FR620 to understand it.
# https://forums.garmin.com/showthread.php?79555-when-will-garmin-express-mac-be-able-to-sync-GPS-EPO-bin-file-on-fenix-2&p=277398#post277398
# The 2304 bytes consist of 32 sets of 72 byte GPS satellite data.
# http://www.vis-plus.ee/pdf/SIM28_SIM68R_SIM68V_EPO-II_Protocol_V1.00.pdf
def fix(epo)
unless epo.length == 28 * 2307
Log.error "GPS data has unexpected length of #{epo.length} bytes"
return nil
end
epo_fixed = ''
0.upto(27) do |i|
offset = i * 2307
# The fill bytes always seem to be 0. Let's issue a warning in case
# this ever changes.
unless epo[offset].to_i == 0 &&
epo[offset + 1].to_i == 0 &&
epo[offset + 2].to_i == 0
Log.warning "EPO fill bytes are not 0 bytes"
end
epo_fixed += epo[offset + 3, 2304]
end
epo_fixed
end
def check_epo_data(epo)
# Convert EPO string into Array of bytes.
epo = epo.bytes.to_a
unless epo.length == 28 * 72 * 32
Log.error "EPO file has wrong length (#{epo.length})"
return false
end
date_1980_01_01 = Time.parse("1980-01-01T00:00:00+00:00")
now = Time.now
largest_date = nil
# Split the EPO data into Arrays of 32 * 72 bytes.
epo.each_slice(32 * 72).to_a.each do |epo_set|
# For each of the 32 satellites we have 72 bytes of data.
epo_set.each_slice(72).to_a.each do |sat|
# The last byte is an XOR checksum of the first 71 bytes.
xor = 0
0.upto(70) { |i| xor ^= sat[i] }
unless xor == sat[71]
Log.error "Checksum error in EPO file"
return false
end
# The first 3 bytes of every satellite record look like a timestamp.
# I assume they are hours after January 1st, 1980 UTC. They probably
# indicate the start of the 6 hour window that the data is for.
hours_after_1980_01_01 = sat[0] | (sat[1] << 8) | (sat[2] << 16)
date = date_1980_01_01 + hours_after_1980_01_01 * 60 * 60
# Either the start point (1980-01-01) is not correct or Garmin is
# publishing data that can be up to 5 days old. We check the date
# with some more relaxed ranges.
if date > now + 8 * 24 * 60 * 60
Log.warn "EPO timestamp (#{date}) is in the future"
elsif date < now - 8 * 24 * 60 * 60
Log.warn "EPO timestamp (#{date}) is too old"
end
largest_date = date if largest_date.nil? || date > largest_date
end
end
Log.info "EPO data is valid until #{largest_date + 6 * 60 * 60}."
true
end
def write_file(output_file, data)
begin
File.write(output_file, data)
rescue IOError
Log.fatal "Cannot write EPO file '#{output_file}': #{$!}"
end
end
end
end
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