UoSAT Standard Variable Timebase Telemetry-Type Data File Format
(USVTTTDFF)

Author      : Jeff Ward
Modified by : W. T. Ong  7/2/91

Revision 2.1A

ASCII file format for telemetry, WOD, and other data.

This file format is used as "common ground" among data collection, analysis 
and display programs.  It was devised to work with telemetry data from real-
time telemetry frames or WOD frames, and can be extended to convey any 
time tagged data.

In the following discussion, a "reading program" is one that reads
USVTTTDFF files for display or analysis, and a "writing program" is
one that writes USVTTTDFF files.

In general, a well-behaved writing program will not put trailing
spaces on lines, and will end every line with 0d hex followed 0a hex
- ASCII CR, LF.  Of course, well-behaved reading programs will not
depend on this!

DATA LINES

Any line not beginning with a "$" is a data line.  Data lines are of the 
following format:

<channel>, <value> [,<value> ...]

<channel> is a decimal channel number. Channel numbers should relate 
the data to calibration information found in a .CFG file. (Described
elsewhere.)

<value> is a decimal data value for that channel.  

Programs should support values between +32768 and -32768.

[If multiple <value> fields follow a single channel, these are assumed
to be sub-multiplexed telemetry points sampled "simultaneously." This
feature may soon be removed.]

OTHER LINES

All other lines begin with "$" followed by a line-type character.  The
line- type character may be in either upper or lower case, although
upper case is preferred.

$H <HeaderComment>

Header.  <HeaderComment> can be any ASCII string.  Ignored by reading
programs, can be anywhere in the file.

$I <SatNumber>

Satellite identifier.  <SatNumber> is a string (terminated by a space
or carriage return) used to identify the satellite to which the data
pertains.  For example, 
              2                will be displayed as UoSAT-2,
              3                will be displayed as UoSAT-3,
              F                will be displayed as UoSAT-F, etc.

If the <SatNumber> string is more than one character long, then the
entire string will be taken as the satellite identifier. For example,
              UoSAT-5          will be displayed as UoSAT-5,
              MySAT1           will be displayed as MySAT1,
              Our_Sat_2        will be displayed as Our_Sat_2, etc.

Satellite number should preceed any data in the file. 

$F <ConfigFile>

Identifies a configuration file which is associated with the data in
the file.  Configuration files are standard format files which
provide channel names, equations to convert raw channel data to
engineering values, etc.

$C <NoOfChannels> <Chan>, [<Chan>, ...]

An optional feature.

Primarily used in WOD files and other files which contain a limited
number of channels. This line will preceed all data points.  

<NoOfChannels> tells how many channels are sampled in the survey.  The
correct number of <Chan> entries should follow, giving the channel
numbers which are in the survey.

Writing programs should include a $C line to help reading programs
limit their menu choices. Reading programs should not assume that a
$C line will be found in a valid file. Furthermore, reading programs
CANNOT assume that if there is a $C line, all of the listed channels
will be available at every $T time point.

$T <Time>

Gives the time at which any following data points were sampled.  

<Time> is an unsigned 32-bit decimal integer counting seconds since midnight on 
January 1, 1970.  This is the standard timestamp in ANSI C.

There may be no data lines following a $T line.

Data lines always refer to the most recent preceeding $T line.

Files without $T lines are valid, but not for much.

Time will always increase when reading through a file.