Latest revision |
Your text |
Line 1: |
Line 1: |
| acquire packets like: | | acquire packets like: |
| strace -p $(pidof location-daemon) -e read=6 2>&1|grep '| 000' | | strace -p $(pidof location-daemon) -e read=6 2>&1|grep '| 000' |
- |
| |
- | alternatively you can capture them from the network interface, but this will include other modem information:
| |
- | tcpdump -i phonet0 -s 0 -w phonet.cap
| |
| | | |
| == Packet Graph == | | == Packet Graph == |
Line 33: |
Line 30: |
| | 000c0 09 08 00 0c xx xx xx xx xx xx xx xx | | | 000c0 09 08 00 0c xx xx xx xx xx xx xx xx |
| DL---------------------------------- | | DL---------------------------------- |
- |
| |
- | B9 BE 67 48 2D 08 AC 08 CC AF 0A EC 49 B5 C8 08 A8 0C 49 49 95 75 4C E8 8C 84 6B 8E EC 29 78 10 10 44 00 18 EF 8E EC 48 91 10 04 EA 18 EA 8E 8C A7 11 FE
| |
| | | |
| === Key === | | === Key === |
Line 53: |
Line 48: |
| == Packet Analysis == | | == Packet Analysis == |
| *??? = mode: The mode of the fix | | *??? = mode: The mode of the fix |
- | *??? = fields: A bitfield representing which items of this tuple contain valid data | + | *??? = fields: A bitfield representing which items of this tuple contain valid data |
- | *00 = ISI sequence ID (seems to be always 0 for GPS)
| + | |
- | *01 = GPS Data Opcode (0x92)
| + | |
| *10,11 = time year | | *10,11 = time year |
| *12 = time month | | *12 = time month |
Line 62: |
Line 55: |
| *16 = time minute | | *16 = time minute |
| *18,19 = time seconds and milliseconds (in milliseconds) | | *18,19 = time seconds and milliseconds (in milliseconds) |
- | *1a,1b = *probably* ept: Time accuracy, but *always* 0, so no way to verify | + | *??? = ept: Time accuracy |
- | *20,21,22,23 = latitude / 360 * 256*256*256*256 | + | *20,21,22(,23?) = latitude / 360 * 256*256*256(*256?) |
- | *24,25,26,27 = longitude / 360 * 256*256*256*256 | + | *24,25,26(,27?) = longitude / 360 * 256*256*256(*256?) |
| *28 = | | *28 = |
| *2b,2c = 0590-12a9 (hex) | | *2b,2c = 0590-12a9 (hex) |
| *2e,2f = eph (cm) | | *2e,2f = eph (cm) |
| + | *??? = altitude: Fix altitude in meters |
| *30 = | | *30 = |
- | *32,33,,36,37 = altitude; ((p32;33) - (p36;37)) / 2 = meters
| |
| *(34?,)35 = (double epv: Vertical position accuracy) * 2 | | *(34?,)35 = (double epv: Vertical position accuracy) * 2 |
| *3c,3d = track: Direction of motion in hundredths of a degree | | *3c,3d = track: Direction of motion in hundredths of a degree |
| *3e,3f = epd: Track accuracy (in hundredths?) | | *3e,3f = epd: Track accuracy (in hundredths?) |
| *42,43 = speed, in centimetres per second | | *42,43 = speed, in centimetres per second |
- | *44,45 = eps: speed accuracy, in centimetres per second | + | *??? = eps: Speed accuracy |
- | *46,47 = climb: Current rate of climb in cm/s | + | *??? = climb: Current rate of climb in m/s |
- | *48,4a = epc: Climb accuracy, in cm/s | + | *??? = epc: Climb accuracy |
- | | + | *45 = |
- | == Protocol Details ==
| + | |
- | | + | |
- | NOTE: I am counting octets based on zero.
| + | |
- | | + | |
- | The actual packets are comprised of "sub-packets".
| + | |
- | The overall packet has a 12 byte header.
| + | |
- | The number of sub-packets is located at octet 8 (and possibly little-endian extended to octet 11).
| + | |
- | | + | |
- | Each subpacket has a 4 byte header:
| + | |
- | * Octet 0 is always 9 | + | |
- | * Octet 1 is the subpacket type
| + | |
- | * Octet 2 is always 0
| + | |
- | * Octet 3 is the length of the subpacket (which includes the subpacket header itself)
| + | |
- | | + | |
- | Subpacket 2 contains position information:
| + | |
- | * Octets 0-3 are the latitude
| + | |
- | * Octets 4-7 are the longitude
| + | |
- | * Octets 12-15 are "eph" (in centimetres)
| + | |
- | * Octets 18-23 are the altitude (and accuracy information)
| + | |
- | | + | |
- | Subpacket 3 contains date and time information:
| + | |
- | * Octets 0-1 are the year
| + | |
- | * Octet 2 is the month
| + | |
- | * Octet 3 is the day of month
| + | |
- | * Octet 5 is the hour
| + | |
- | * Octet 6 is the minute
| + | |
- | * Octets 8-9 are milliseconds (including seconds)
| + | |
- | * Octets 10-11 are the time accuracy
| + | |
- | | + | |
- | Subpacket 4 contains information on track, speed, and climb:
| + | |
- | * Octets 0-1 are track (direction of motion) in cm/sec
| + | |
- | * Octets 2-3 are the track accuracy
| + | |
- | * Octets 6-7 are the speed in cm/sec
| + | |
- | * Octets 8-9 are speed accuracy
| + | |
- | * Octets 8-11 are climb in cm/sec
| + | |
- | * Octets 12-13 are climb accuracy
| + | |
- | | + | |
- | Subpacket 5 contains satellite information:
| + | |
- | * Octet 0 is the number of sats visible
| + | |
- | * Beginning with octet 8, there are series of 12-octet info for each sat visible:
| + | |
- | ** Octet 1 is the PRN
| + | |
- | ** Octet 2 is 1 if the sat is being used, and 0 otherwise
| + | |
- | ** Octets 3-4 are the signal strength
| + | |
- | ** Octets 6-7 are the elevation
| + | |
- | ** Octets 8-9 are the azimuth
| + | |
- | | + | |
- | Subpacket 7 contains information on the GSM cellular network:
| + | |
- | ** Octets 0-1 contain the Mobile Country Code
| + | |
- | ** Octets 2-3 contain the Mobile Network Code
| + | |
- | ** Octets 4-5 contain the Location Area Code
| + | |
- | ** Octets 6-7 contain the Cell ID
| + | |
- | | + | |
- | Subpacket 8 contains information on the WCDMA cellular network:
| + | |
- | ** Octets 0-1 contain the Mobile Country Code
| + | |
- | ** Octets 2-3 contain the Mobile Network Code
| + | |
- | ** Octets 4-7 contain the UC ID
| + | |
- | | + | |
- | == Wireshark == | + | |
- | | + | |
- | [[User:sre|Sebastian Reichel]] writes a lowlevel library to access the N900's modem features and a wireshark plugin to analyze the packages. The information from above is currently only included in the Wireshark Plugin:
| + | |
- | | + | |
- | * [http://elektranox.org/n900/images/wireshark/04.png Screenshot]
| + | |
- | * [https://git.ring0.de/isi-wireshark-plugin/ Plugin]
| + | |
- | | + | |
- | [http://maemo.org/profile/view/luke-jr Luke Dashjr] wrote small program in C which show GPS data from phonet modem stack.
| + | |
- | | + | |
- | * [http://luke.dashjr.org/tmp/code/gps2.c gps2.c]
| + | |
- | | + | |
- | [[Category:N900 Hardware]]
| + | |