A.R.Drone Developer Guide - Abstract

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6.1 AT Commands syntax
Strings are encoded as 8-bit ASCII characters, with a Line Feed character (byte value 10(10)),
noted hereafter, as a newline delimiter.
One command consists in the three characters AT* (i.e. three 8-bit words with values 41(16),54(16),2a(16))
followed by a command name, and equal sign, a sequence number, and optionally a list of
comma-separated arguments whose meaning depends on the command.
A single UDP packet can contain one or more commands, separated by newlines (byte value
0A(16)). An AT command must reside in a single UDP packet. Splitting an AT command in two
or more UDP packets is not possible.
Example :
AT*PCMD=21625,1,0,0,0,0AT*REF=21626,290717696
The maximum length of the total command cannot exceed 1024 characters; otherwise the entire
command line is rejected. This limit is hard coded in the drone software.
Note : Incorrect AT commands should be ignored by the drone. Nevertheless, the client should
always make sure it sends correctly formed UDP packets.
Most commands will accept arguments, which can be of three different type :
• A signed integer, stored in the command string with a decimal representation (ex: the
sequence number)
• A string value stored between double quotes (ex: the arguments of AT*CONFIG)
• A single-precision IEEE-754 floating-point value (aka. float). Those are never directly
stored in the command string. Instead, the 32-bit word containing the float will be considered
as a 32-bit signed integer and printed in the AT command (an example is given
below).
6.2 Commands sequencing
In order to avoid the drone from processing old commands, a sequence number is associated
to each sent AT command, and is stored as the first number after the "equal" sign. The drone
will not execute any command whose sequence number is less than the last valid received AT-
Command sequence number. This sequence number is reset to 1 inside the drone every time
a client disconnects from the AT-Command UDP port (currently this disconnection is done by
not sending any command during more than 2 seconds), and when a command is received
with a sequence number set to 1.
A client MUST thus respect the following rule in order to successfully execute commands on
the drone :