+++ /dev/null
-<?xml version="1.0" encoding="utf-8" ?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
-"/usr/share/xml/docbook/schema/dtd/4.5/docbookx.dtd">
-
-<article>
- <articleinfo>
- <title>AltOS Telemetry</title>
- <subtitle>Packet Definitions</subtitle>
- <author>
- <firstname>Keith</firstname>
- <surname>Packard</surname>
- </author>
- <copyright>
- <year>2011</year>
- <holder>Keith Packard</holder>
- </copyright>
- <legalnotice>
- <para>
- This document is released under the terms of the
- <ulink url="http://creativecommons.org/licenses/by-sa/3.0/">
- Creative Commons ShareAlike 3.0
- </ulink>
- license.
- </para>
- </legalnotice>
- <revhistory>
- <revision>
- <revnumber>0.1</revnumber>
- <date>01 July 2011</date>
- <revremark>Initial content</revremark>
- </revision>
- </revhistory>
- </articleinfo>
- <section>
- <title>Packet Format Design</title>
- <para>
- AltOS telemetry data is split into multiple different packets,
- all the same size, but each includs an identifier so that the
- ground station can distinguish among different types. A single
- flight board will transmit multiple packet types, each type on a
- different schedule. The ground software need look for only a
- single packet size, and then decode the information within the
- packet and merge data from multiple packets to construct the
- full flight computer state.
- </para>
- <para>
- Each AltOS packet is 32 bytes long. This size was chosen based
- on the known telemetry data requirements. The power of two size
- allows them to be stored easily in flash memory without having
- them split across blocks or leaving gaps at the end.
- </para>
- <para>
- All packet types start with a five byte header which encodes the
- device serial number, device clock value and the packet
- type. The remaining 27 bytes encode type-specific data.
- </para>
- </section>
- <section>
- <title>Packet Formats</title>
- This section first defines the packet header common to all packets
- and then the per-packet data layout.
- <section>
- <title>Packet Header</title>
- <table frame='all'>
- <title>Telemetry Packet Header</title>
- <tgroup cols='4' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='center' colwidth='3*' colname='Data Type'/>
- <colspec align='left' colwidth='3*' colname='Name'/>
- <colspec align='left' colwidth='9*' colname='Description'/>
- <thead>
- <row>
- <entry align='center'>Offset</entry>
- <entry align='center'>Data Type</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0</entry>
- <entry>uint16_t</entry>
- <entry>serial</entry>
- <entry>Device serial Number</entry>
- </row>
- <row>
- <entry>2</entry>
- <entry>uint16_t</entry>
- <entry>tick</entry>
- <entry>Device time in 100ths of a second</entry>
- </row>
- <row>
- <entry>4</entry>
- <entry>uint8_t</entry>
- <entry>type</entry>
- <entry>Packet type</entry>
- </row>
- <row>
- <entry>5</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- <para>
- Each packet starts with these five bytes which serve to identify
- which device has transmitted the packet, when it was transmitted
- and what the rest of the packet contains.
- </para>
- </section>
- <section>
- <title>Sensor Data</title>
- <informaltable frame='none' label='' tocentry='0'>
- <tgroup cols='2' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='left' colwidth='3*' colname='Description'/>
- <thead>
- <row>
- <entry>Type</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0x01</entry>
- <entry>TeleMetrum Sensor Data</entry>
- </row>
- <row>
- <entry>0x02</entry>
- <entry>TeleMini Sensor Data</entry>
- </row>
- <row>
- <entry>0x03</entry>
- <entry>TeleNano Sensor Data</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
- <para>
- TeleMetrum, TeleMini and TeleNano share this same packet
- format for sensor data. Each uses a distinct packet type so
- that the receiver knows which data values are valid and which
- are undefined.
- </para>
- <para>
- Sensor Data packets are transmitted once per second on the
- ground, 10 times per second during ascent and once per second
- during descent and landing
- </para>
- <table frame='all'>
- <title>Sensor Packet Contents</title>
- <tgroup cols='4' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='center' colwidth='3*' colname='Data Type'/>
- <colspec align='left' colwidth='3*' colname='Name'/>
- <colspec align='left' colwidth='9*' colname='Description'/>
- <thead>
- <row>
- <entry align='center'>Offset</entry>
- <entry align='center'>Data Type</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>5</entry><entry>uint8_t</entry><entry>state</entry><entry>Flight state</entry>
- </row>
- <row>
- <entry>6</entry><entry>int16_t</entry><entry>accel</entry><entry>accelerometer (TM only)</entry>
- </row>
- <row>
- <entry>8</entry><entry>int16_t</entry><entry>pres</entry><entry>pressure sensor</entry>
- </row>
- <row>
- <entry>10</entry><entry>int16_t</entry><entry>temp</entry><entry>temperature sensor</entry>
- </row>
- <row>
- <entry>12</entry><entry>int16_t</entry><entry>v_batt</entry><entry>battery voltage</entry>
- </row>
- <row>
- <entry>14</entry><entry>int16_t</entry><entry>sense_d</entry><entry>drogue continuity sense (TM/Tm)</entry>
- </row>
- <row>
- <entry>16</entry><entry>int16_t</entry><entry>sense_m</entry><entry>main continuity sense (TM/Tm)</entry>
- </row>
- <row>
- <entry>18</entry><entry>int16_t</entry><entry>acceleration</entry><entry>m/s² * 16</entry>
- </row>
- <row>
- <entry>20</entry><entry>int16_t</entry><entry>speed</entry><entry>m/s * 16</entry>
- </row>
- <row>
- <entry>22</entry><entry>int16_t</entry><entry>height</entry><entry>m</entry>
- </row>
- <row>
- <entry>24</entry><entry>int16_t</entry><entry>ground_pres</entry><entry>Average barometer reading on ground</entry>
- </row>
- <row>
- <entry>26</entry><entry>int16_t</entry><entry>ground_accel</entry><entry>TM</entry>
- </row>
- <row>
- <entry>28</entry><entry>int16_t</entry><entry>accel_plus_g</entry><entry>TM</entry>
- </row>
- <row>
- <entry>30</entry><entry>int16_t</entry><entry>accel_minus_g</entry><entry>TM</entry>
- </row>
- <row>
- <entry>32</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </section>
- <section>
- <title>Configuration Data</title>
- <informaltable frame='none' label='' tocentry='0'>
- <tgroup cols='2' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='left' colwidth='3*' colname='Description'/>
- <thead>
- <row>
- <entry>Type</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0x04</entry>
- <entry>Configuration Data</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
- <para>
- This provides a description of the software installed on the
- flight computer as well as any user-specified configuration data.
- </para>
- <para>
- Configuration data packets are transmitted once per second
- during all phases of the flight
- </para>
- <table frame='all'>
- <title>Sensor Packet Contents</title>
- <tgroup cols='4' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='center' colwidth='3*' colname='Data Type'/>
- <colspec align='left' colwidth='3*' colname='Name'/>
- <colspec align='left' colwidth='9*' colname='Description'/>
- <thead>
- <row>
- <entry align='center'>Offset</entry>
- <entry align='center'>Data Type</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>5</entry><entry>uint8_t</entry><entry>type</entry><entry>Device type</entry>
- </row>
- <row>
- <entry>6</entry><entry>uint16_t</entry><entry>flight</entry><entry>Flight number</entry>
- </row>
- <row>
- <entry>8</entry><entry>uint8_t</entry><entry>config_major</entry><entry>Config major version</entry>
- </row>
- <row>
- <entry>9</entry><entry>uint8_t</entry><entry>config_minor</entry><entry>Config minor version</entry>
- </row>
- <row>
- <entry>10</entry><entry>uint16_t</entry><entry>main_deploy</entry><entry>Main deploy alt in meters</entry>
- </row>
- <row>
- <entry>12</entry><entry>uint32_t</entry><entry>flight_log_max</entry><entry>Maximum flight log size (B)</entry>
- </row>
- <row>
- <entry>16</entry><entry>char</entry><entry>callsign[8]</entry><entry>Radio operator identifier</entry>
- </row>
- <row>
- <entry>24</entry><entry>char</entry><entry>version[8]</entry><entry>Software version identifier</entry>
- </row>
- <row>
- <entry>32</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </section>
- <section>
- <title>GPS Location</title>
- <informaltable frame='none' label='' tocentry='0'>
- <tgroup cols='2' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='left' colwidth='3*' colname='Description'/>
- <thead>
- <row>
- <entry>Type</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0x05</entry>
- <entry>GPS Location</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
- <para>
- This packet provides all of the information available from the
- Venus SkyTraq GPS receiver—position, time, speed and precision
- estimates.
- </para>
- <para>
- GPS Location packets are transmitted once per second during
- all phases of the flight
- </para>
- <table frame='all'>
- <title>GPS Location Packet Contents</title>
- <tgroup cols='4' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='center' colwidth='3*' colname='Data Type'/>
- <colspec align='left' colwidth='3*' colname='Name'/>
- <colspec align='left' colwidth='9*' colname='Description'/>
- <thead>
- <row>
- <entry align='center'>Offset</entry>
- <entry align='center'>Data Type</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>5</entry><entry>uint8_t</entry><entry>flags</entry>
- <entry>See GPS Flags table below</entry>
- </row>
- <row>
- <entry>6</entry><entry>int16_t</entry><entry>altitude</entry><entry>m</entry>
- </row>
- <row>
- <entry>8</entry><entry>int32_t</entry><entry>latitude</entry><entry>degrees * 10<superscript>7</superscript></entry>
- </row>
- <row>
- <entry>12</entry><entry>int32_t</entry><entry>longitude</entry><entry>degrees * 10<superscript>7</superscript></entry>
- </row>
- <row>
- <entry>16</entry><entry>uint8_t</entry><entry>year</entry>
- </row>
- <row>
- <entry>17</entry><entry>uint8_t</entry><entry>month</entry>
- </row>
- <row>
- <entry>18</entry><entry>uint8_t</entry><entry>day</entry>
- </row>
- <row>
- <entry>19</entry><entry>uint8_t</entry><entry>hour</entry>
- </row>
- <row>
- <entry>20</entry><entry>uint8_t</entry><entry>minute</entry>
- </row>
- <row>
- <entry>21</entry><entry>uint8_t</entry><entry>second</entry>
- </row>
- <row>
- <entry>22</entry><entry>uint8_t</entry><entry>pdop</entry><entry>* 5</entry>
- </row>
- <row>
- <entry>23</entry><entry>uint8_t</entry><entry>hdop</entry><entry>* 5</entry>
- </row>
- <row>
- <entry>24</entry><entry>uint8_t</entry><entry>vdop</entry><entry>* 5</entry>
- </row>
- <row>
- <entry>25</entry><entry>uint8_t</entry><entry>mode</entry>
- <entry>See GPS Mode table below</entry>
- </row>
- <row>
- <entry>26</entry><entry>uint16_t</entry><entry>ground_speed</entry><entry>cm/s</entry>
- </row>
- <row>
- <entry>28</entry><entry>uint8_t</entry><entry>course</entry><entry>/ 2</entry>
- </row>
- <row>
- <entry>29</entry><entry>uint8_t</entry><entry>unused[3]</entry>
- </row>
- <row>
- <entry>32</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- <para>
- Packed into a one byte field are status flags and the count of
- satellites used to compute the position fix. Note that this
- number may be lower than the number of satellites being
- tracked; the receiver will not use information from satellites
- with weak signals or which are close enough to the horizon to
- have significantly degraded position accuracy.
- </para>
- <table frame='all'>
- <title>GPS Flags</title>
- <tgroup cols='3' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='bits'/>
- <colspec align='left' colwidth='2*' colname='name'/>
- <colspec align='left' colwidth='7*' colname='description'/>
- <thead>
- <row>
- <entry align='center'>Bits</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0-3</entry>
- <entry>nsats</entry>
- <entry>Number of satellites in solution</entry>
- </row>
- <row>
- <entry>4</entry>
- <entry>valid</entry>
- <entry>GPS solution is valid</entry>
- </row>
- <row>
- <entry>5</entry>
- <entry>running</entry>
- <entry>GPS receiver is operational</entry>
- </row>
- <row>
- <entry>6</entry>
- <entry>date_valid</entry>
- <entry>Reported date is valid</entry>
- </row>
- <row>
- <entry>7</entry>
- <entry>course_valid</entry>
- <entry>ground speed, course and climb rates are valid</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- <para>
- Here are all of the valid GPS operational modes. Altus Metrum
- products will only ever report 'N' (not valid), 'A'
- (Autonomous) modes or 'E' (Estimated). The remaining modes
- are either testing modes or require additional data.
- </para>
- <table frame='all'>
- <title>GPS Mode</title>
- <tgroup cols='3' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='value'/>
- <colspec align='center' colwidth='3*' colname='name'/>
- <colspec align='left' colwidth='7*' colname='description'/>
- <thead>
- <row>
- <entry align='center'>Mode</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Decsription</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>N</entry>
- <entry>Not Valid</entry>
- <entry>All data are invalid</entry>
- </row>
- <row>
- <entry>A</entry>
- <entry>Autonomous mode</entry>
- <entry>Data are derived from satellite data</entry>
- </row>
- <row>
- <entry>D</entry>
- <entry>Differential Mode</entry>
- <entry>
- Data are augmented with differential data from a
- known ground station. The SkyTraq unit in TeleMetrum
- does not support this mode
- </entry>
- </row>
- <row>
- <entry>E</entry>
- <entry>Estimated</entry>
- <entry>
- Data are estimated using dead reckoning from the
- last known data
- </entry>
- </row>
- <row>
- <entry>M</entry>
- <entry>Manual</entry>
- <entry>Data were entered manually</entry>
- </row>
- <row>
- <entry>S</entry>
- <entry>Simulated</entry>
- <entry>GPS receiver testing mode</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </section>
- <section>
- <title>GPS Satellite Data</title>
- <informaltable frame='none' label='' tocentry='0'>
- <tgroup cols='2' align='center' colsep='1' rowsep='1'>
- <colspec align='center' colwidth='*' colname='Offset'/>
- <colspec align='left' colwidth='3*' colname='Description'/>
- <thead>
- <row>
- <entry>Type</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0x06</entry>
- <entry>GPS Satellite Data</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
- <para>
- This packet provides space vehicle identifiers and signal
- quality information in the form of a C/N1 number for up to 12
- satellites. The order of the svids is not specified.
- </para>
- <para>
- GPS Satellite data are transmitted once per second during all
- phases of the flight.
- </para>
- <table frame='all'>
- <title>GPS Satellite Data Contents</title>
- <tgroup cols='4' align='center' colsep='1' rowsep='1'>
- <colspec align='right' colwidth='*' colname='Offset'/>
- <colspec align='center' colwidth='3*' colname='Data Type'/>
- <colspec align='left' colwidth='3*' colname='Name'/>
- <colspec align='left' colwidth='9*' colname='Description'/>
- <thead>
- <row>
- <entry align='center'>Offset</entry>
- <entry align='center'>Data Type</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>5</entry><entry>uint8_t</entry><entry>channels</entry>
- <entry>Number of reported satellite information</entry>
- </row>
- <row>
- <entry>6</entry><entry>sat_info_t</entry><entry>sats[12]</entry>
- <entry>See Per-Satellite data table below</entry>
- </row>
- <row>
- <entry>30</entry><entry>uint8_t</entry><entry>unused[2]</entry>
- </row>
- <row>
- <entry>32</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- <table frame='all'>
- <title>GPS Per-Satellite data (sat_info_t)</title>
- <tgroup cols='4' align='center' colsep='1' rowsep='1'>
- <colspec align='right' colwidth='*' colname='Offset'/>
- <colspec align='center' colwidth='3*' colname='Data Type'/>
- <colspec align='left' colwidth='3*' colname='Name'/>
- <colspec align='left' colwidth='9*' colname='Description'/>
- <thead>
- <row>
- <entry align='center'>Offset</entry>
- <entry align='center'>Data Type</entry>
- <entry align='center'>Name</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>0</entry><entry>uint8_t</entry><entry>svid</entry>
- <entry>Space Vehicle Identifier</entry>
- </row>
- <row>
- <entry>1</entry><entry>uint8_t</entry><entry>c_n_1</entry>
- <entry>C/N1 signal quality indicator</entry>
- </row>
- <row>
- <entry>2</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </section>
- </section>
- <section>
- <title>Data Transmission</title>
- <para>
- Altus Metrum devices use the Texas Instruments CC1111
- microcontroller which includes an integrated sub-GHz digital
- transceiver. This transceiver is used to both transmit and
- receive the telemetry packets. This section discusses what
- modulation scheme is used and how this device is configured.
- </para>
- <section>
- <title>Modulation Scheme</title>
- <para>
- Texas Instruments provides a tool for computing modulation
- parameters given a desired modulation format and basic bit
- rate. For AltOS, the basic bit rate was specified as 38 kBaud,
- resulting in the following signal parmeters:
- </para>
- <table>
- <tgroup cols='3'>
- <colspec align="center" colwidth="*" colname="parameter"/>
- <colspec align="center" text-align="." colwidth="*" colname="value"/>
- <colspec align="center" colwidth="*" colname="description"/>
- <thead>
- <row>
- <entry align='center'>Parameter</entry>
- <entry align='center'>Value</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>Modulation</entry>
- <entry>GFSK</entry>
- <entry>Gaussian Frequency Shift Keying</entry>
- </row>
- <row>
- <entry>Deviation</entry>
- <entry>20.507812 kHz</entry>
- <entry>Frequency modulation</entry>
- </row>
- <row>
- <entry>Data rate</entry>
- <entry>38.360596 kBaud</entry>
- <entry>Raw bit rate</entry>
- </row>
- <row>
- <entry>RX Filter Bandwidth</entry>
- <entry>93.75 kHz</entry>
- <entry>Receiver Band pass filter bandwidth</entry>
- </row>
- <row>
- <entry>IF Frequency</entry>
- <entry>140.62 kHz</entry>
- <entry>Receiver intermediate frequency</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </section>
- <section>
- <para>
- The cc1111 provides forward error correction in hardware,
- which AltOS uses to improve reception of weak signals. The
- overall effect of this is to halve the available bandwidth for
- data from 38 kBaud to 19 kBaud.
- </para>
- <title>Error Correction</title>
- <table>
- <tgroup cols='3'>
- <colspec align="center" colwidth="*" colname="parameter"/>
- <colspec align="center" colwidth="*" colname="value"/>
- <colspec align="center" colwidth="*" colname="description"/>
- <thead>
- <row>
- <entry align='center'>Parameter</entry>
- <entry align='center'>Value</entry>
- <entry align='center'>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>Error Correction</entry>
- <entry>Convolutional coding FEC</entry>
- <entry>1/2 code, constraint length m=4</entry>
- </row>
- <row>
- <entry>Interleaving</entry>
- <entry>4 x 4</entry>
- <entry>Reduce effect of noise burst</entry>
- </row>
- <row>
- <entry>Data Whitening</entry>
- <entry>XOR with 9-bit PNR</entry>
- <entry>Rotate right with bit 8 = bit 0 xor bit 5, initial
- value 111111111</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </section>
- </section>
- <section>
- <title>History and Motivation</title>
- <para>
- The original AltoOS telemetry mechanism encoded everything
- available piece of information on the TeleMetrum hardware into a
- single unified packet. Initially, the packets contained very
- little data—some raw sensor readings along with the current GPS
- coordinates when a GPS receiver was connected. Over time, the
- amount of data grew to include sensor calibration data, GPS
- satellite information and a host of internal state information
- designed to help diagnose flight failures in case of a loss of
- the on-board flight data.
- </para>
- <para>
- Because every packet contained all of the data, packets were
- huge—95 bytes long. Much of the information was also specific to
- the TeleMetrum hardware. With the introduction of the TeleMini
- flight computer, most of the data contained in the telemetry
- packets was unavailable. Initially, a shorter, but still
- comprehensive packet was implemented. This required that the
- ground station be pre-configured as to which kind of packet to
- expect.
- </para>
- <para>
- The development of several companion boards also made the
- shortcomings evident—each companion board would want to include
- telemetry data in the radio link; with the original design, the
- packet would have to hold the new data as well, requiring
- additional TeleMetrum and ground station changes.
- </para>
- </section>
-</article>
projects / fw / altos / blobdiff