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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>AltOS Companion Port</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="article"><div class="titlepage"><div><div><h2 class="title"><a name="idm46040259592256"></a>AltOS Companion Port</h2></div><div><h3 class="subtitle"><i>Protocol Definitions</i></h3></div><div><div class="author"><h3 class="author"><span class="firstname">Keith</span> <span class="surname">Packard</span></h3></div></div><div><p class="copyright">Copyright © 2012 Keith Packard</p></div><div><div class="legalnotice"><a name="idm46040233083952"></a><p>
This document is released under the terms of the
<a class="ulink" href="http://creativecommons.org/licenses/by-sa/3.0/" target="_top">
Creative Commons ShareAlike 3.0
</a>
license.
</p></div></div><div><div class="revhistory"><table style="border-style:solid; width:100%;" summary="Revision History"><tr><th align="left" valign="top" colspan="2"><b>Revision History</b></th></tr><tr><td align="left">Revision 0.1</td><td align="left">13 January 2012</td></tr><tr><td align="left" colspan="2">Initial content</td></tr></table></div></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idm46040232383776">1. Companion Port</a></span></dt><dt><span class="section"><a href="#idm46040232379280">2. Companion SPI Protocol</a></span></dt><dt><span class="section"><a href="#idm46040232376384">3. SPI Message Formats</a></span></dt><dd><dl><dt><span class="section"><a href="#idm46040232375104">3.1. Command Message</a></span></dt><dt><span class="section"><a href="#idm46040233245360">3.2. SETUP reply message</a></span></dt><dt><span class="section"><a href="#idm46040233223824">3.3. FETCH reply message</a></span></dt></dl></dd><dt><span class="section"><a href="#idm46040227732240">4. History and Motivation</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idm46040232383776"></a>1. Companion Port</h2></div></div></div><p>
Many Altus Metrum products come with an eight pin Micro MaTch
connector, called the Companion Port. This is often used to
program devices using a programming cable. However, it can also
be used to connect TeleMetrum to external companion boards
(hence the name).
</p><p>
The Companion Port provides two different functions:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
Power. Both battery-level and 3.3V regulated power are
available. Note that the amount of regulated power is not
huge; TeleMetrum contains a 150mA regulator and uses, at
peak, about 120mA or so. For applications needing more than
a few dozen mA, placing a separate regulator on them and
using the battery for power is probably a good idea.
</p></li><li class="listitem"><p>
SPI. The flight computer operates as a SPI master, using
a protocol defined in this document. Companion boards
provide a matching SPI slave implementation which supplies
telemetry information for the radio downlink during flight
</p></li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idm46040232379280"></a>2. Companion SPI Protocol</h2></div></div></div><p>
The flight computer implements a SPI master communications
channel over the companion port, and uses this to get
information about a connected companion board and then to get
telemetry data for transmission during flight.
</p><p>
At startup time, the flight computer sends a setup request
packet, and the companion board returns a board identifier, the
desired telemetry update period and the number of data channels
provided. The flight computer doesn't interpret the telemetry
data at all, simply packing it up and sending it over the link.
Telemetry packets are 32 bytes long, and companion packets use 8
bytes as a header leaving room for a maximum of 12 16-bit data
values.
</p><p>
Because of the limits of the AVR processors used in the first
two companion boards, the SPI data rate is set to 187.5kbaud.
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idm46040232376384"></a>3. SPI Message Formats</h2></div></div></div><p>
This section first defines the command message format sent from
the flight computer to the companion board, and then the various
reply message formats for each type of command message.
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm46040232375104"></a>3.1. Command Message</h3></div></div></div><div class="table"><a name="idm46040232374432"></a><p class="title"><b>Table 1. Companion Command Message</b></p><div class="table-contents"><table summary="Companion Command Message" border="1"><colgroup><col align="center" class="Offset"><col align="center" class="Data Type"><col align="left" class="Name"><col align="left" class="Description"></colgroup><thead><tr><th align="center">Offset</th><th align="center">Data Type</th><th align="center">Name</th><th align="center">Description</th></tr></thead><tbody><tr><td align="center">0</td><td align="center">uint8_t</td><td align="left">command</td><td align="left">Command identifier</td></tr><tr><td align="center">1</td><td align="center">uint8_t</td><td align="left">flight_state</td><td align="left">Current flight computer state</td></tr><tr><td align="center">2</td><td align="center">uint16_t</td><td align="left">tick</td><td align="left">Flight computer clock (100 ticks/second)</td></tr><tr><td align="center">4</td><td align="center">uint16_t</td><td align="left">serial</td><td align="left">Flight computer serial number</td></tr><tr><td align="center">6</td><td align="center">uint16_t</td><td align="left">flight</td><td align="left">Flight number</td></tr><tr><td align="center">8</td><td class="auto-generated"> </td><td class="auto-generated"> </td><td class="auto-generated"> </td></tr></tbody></table></div></div><br class="table-break"><div class="table"><a name="idm46040233261392"></a><p class="title"><b>Table 2. Companion Command Identifiers</b></p><div class="table-contents"><table summary="Companion Command Identifiers" border="1"><colgroup><col align="center" class="Value"><col align="left" class="Name"><col align="left" class="Description"></colgroup><thead><tr><th align="center">Value</th><th align="left">Name</th><th align="left">Description</th></tr></thead><tbody><tr><td align="center">1</td><td align="left">SETUP</td><td align="left">Supply the flight computer with companion
information</td></tr><tr><td align="center">2</td><td align="left">FETCH</td><td align="left">Return telemetry information</td></tr><tr><td align="center">3</td><td align="left">NOTIFY</td><td align="left">Tell companion board when flight state
changes</td></tr></tbody></table></div></div><br class="table-break"><p>
The flight computer will send a SETUP message shortly after
power-up and will then send FETCH messages no more often than
the rate specified in the SETUP reply. NOTIFY messages will be
sent whenever the flight state changes.
</p><p>
'flight_state' records the current state of the flight,
whether on the pad, under power, coasting to apogee or
descending on the drogue or main chute.
</p><p>
'tick' provides the current flight computer clock, which
be used to synchronize data recorded on the flight computer
with that recorded on the companion board in post-flight analysis.
</p><p>
'serial' is the product serial number of the flight computer,
'flight' is the flight sequence number. Together, these two
uniquely identify the flight and can be recorded with any
companion board data logging to associate the companion data
with the proper flight.
</p><p>
NOTIFY commands require no reply at all, they are used solely
to inform the companion board when the state of the flight, as
computed by the flight computer, changes. Companion boards can
use this to change data collection parameters, disabling data
logging until the flight starts and terminating it when the
flight ends.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm46040233245360"></a>3.2. SETUP reply message</h3></div></div></div><div class="table"><a name="idm46040233244688"></a><p class="title"><b>Table 3. SETUP reply contents</b></p><div class="table-contents"><table summary="SETUP reply contents" border="1"><colgroup><col align="center" class="Offset"><col align="center" class="Data Type"><col align="left" class="Name"><col align="left" class="Description"></colgroup><thead><tr><th align="center">Offset</th><th align="center">Data Type</th><th align="center">Name</th><th align="center">Description</th></tr></thead><tbody><tr><td align="center">0</td><td align="center">uint16_t</td><td align="left">board_id</td><td align="left">Board identifier</td></tr><tr><td align="center">2</td><td align="center">uint16_t</td><td align="left">board_id_inverse</td><td align="left">~board_id—used to tell if a board is present</td></tr><tr><td align="center">4</td><td align="center">uint8_t</td><td align="left">update_period</td><td align="left">Minimum time (in 100Hz ticks) between FETCH commands</td></tr><tr><td align="center">5</td><td align="center">uint8_t</td><td align="left">channels</td><td align="left">Number of data channels to retrieve in FETCH command</td></tr><tr><td align="center">6</td><td class="auto-generated"> </td><td class="auto-generated"> </td><td class="auto-generated"> </td></tr></tbody></table></div></div><br class="table-break"><p>
The SETUP reply contains enough information to uniquely
identify the companion board to the end user as well as for
the flight computer to know how many data values to expect in
reply to a FETCH command, and how often to fetch that data.
</p><p>
To detect the presence of a companion board, the flight
computer checks to make sure that board_id_inverse is the
bit-wise inverse of board_id. Current companion boards use
USB product ID as the board_id, but the flight computer does
not interpret this data and so it can be any value.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm46040233223824"></a>3.3. FETCH reply message</h3></div></div></div><div class="table"><a name="idm46040227748144"></a><p class="title"><b>Table 4. FETCH reply contents</b></p><div class="table-contents"><table summary="FETCH reply contents" border="1"><colgroup><col align="center" class="Offset"><col align="center" class="Data Type"><col align="left" class="Name"><col align="left" class="Description"></colgroup><thead><tr><th align="center">Offset</th><th align="center">Data Type</th><th align="center">Name</th><th align="center">Description</th></tr></thead><tbody><tr><td align="center">0</td><td align="center">uint16_t</td><td align="left">data0</td><td align="left">0th data item</td></tr><tr><td align="center">2</td><td align="center">uint16_t</td><td align="left">data1</td><td align="left">1st data item</td></tr><tr><td align="center">...</td><td class="auto-generated"> </td><td class="auto-generated"> </td><td class="auto-generated"> </td></tr></tbody></table></div></div><br class="table-break"><p>
The FETCH reply contains arbitrary data to be reported over
the flight computer telemetry link. The number of 16-bit data items
must match the 'channels' value provided in the SETUP reply
message.
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idm46040227732240"></a>4. History and Motivation</h2></div></div></div><p>
To allow cross-programming, the original TeleMetrum and
TeleDongle designs needed to include some kind of
connector. With that in place, adding the ability to connect
external cards to TeleMetrum was fairly simple. We set the
software piece of this puzzle aside until we had a companion
board to use.
</p><p>
The first companion board was TeleScience. Designed to collect
temperature data from the nose and fin of the airframe, the main
requirement for the companion port was that it be able to report
telemetry data during flight as a back-up in case the
TeleScience on-board data was lost.
</p><p>
The second companion board, TelePyro, provides 8 additional
channels for deployment, staging or other activities. To avoid
re-programming the TeleMetrum to use TelePyro, we decided to
provide enough information over the companion link for it to
independently control those channels.
</p><p>
Providing a standard, constant interface between the flight
computer and companion boards allows for the base flight
computer firmware to include support for companion boards.
</p></div></div></body></html>
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