diff options
| -rw-r--r-- | README.md | 16 | ||||
| -rw-r--r-- | lib/postrunner/EPO_Downloader.rb | 48 |
2 files changed, 54 insertions, 10 deletions
@@ -80,6 +80,22 @@ This will provide you with a lot more information contained in the FIT files that is not available through Garmin Connect or most other tools. +When you upload your FIT data to the Garmin Connect site using WiFi or +Garmin Software, your device will be updated with 7 days worth of +Extended Prediction Orbit (EPO) data. The GPS receiver in your device +can use this data to acquire GPS locks much faster during the next 7 +days. To fetch the current set of EPO data, just use the following +command while you have your device mounted via USB. + +``` +$ postrunner update-gps +``` + +This was tested on the FR620 and will probably also work on the FR220. +Other devices may work, but you use this at your own risk. This +feature will download a file called EPO.BIN and copy it to +GARMIN/REMOTESW/EPO.BIN. + ### Viewing FIT file data in your web browser You can also view the full details of your activity in your browser. diff --git a/lib/postrunner/EPO_Downloader.rb b/lib/postrunner/EPO_Downloader.rb index 6121d20..30ccd9f 100644 --- a/lib/postrunner/EPO_Downloader.rb +++ b/lib/postrunner/EPO_Downloader.rb @@ -15,9 +15,9 @@ require 'net/http' module PostRunner - # This class can download the current set of ephemeris 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. + # 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') @@ -38,15 +38,17 @@ module PostRunner @request.body = @@POST_DATA end - # Download the current ephemeris data from the Garmin server and write it - # into the specified output file. + # 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 "GPS caching data has been downloaded from Garmin site." + Log.info "Extended Prediction Orbit (EPO) data has been downloaded " + + "from Garmin site." true end @@ -56,16 +58,18 @@ module PostRunner def get_epo_from_server res = @http.request(@request) if res.code.to_i != 200 - Log.error "GPS data download failed: #{res}" + Log.error "Extended Orbit Prediction (EPO) data download failed: #{res}" return nil end res.body end - # The downloaded data contains ephemeris data for 6 hour windows for 7 - # days. Each window set is 2307 bytes long, but the first 3 bytes must - # be removed for the FR620 to understand it. + # 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" @@ -81,6 +85,30 @@ module PostRunner 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 + # 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 + end + end + + true + end + def write_file(output_file, data) begin File.write(output_file, data) |