A.R.Drone Developer Guide - Abstract

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All the blocks share this common structure :
Listing 7.1: Navdata option structure
typedef struct _navdata_option_t {
uint16_t tag; /* Tag for a specific option */
uint16_t size; /* Length of the struct */
uint8_t data[]; /* Structure complete with the special tag */
} navdata_option_t;
The most important options are navdata_demo_t, navdata_cks_t, navdata_host_angles_t and
navdata_vision_detect_t. Their content can be found in the C structure, mainly in the navdata_common.h.
7.1.2 Initiating the reception of Navigation data
To receive Navdata, you must send a packet of some bytes on the port NAVDATA_PORT of host.
Two cases :
• the drone starts in bootstrap mode, only the status and the sequence counter are sent.
• the Drone is always started, Navdata demo are send.
To exit BOOTSTRAP mode, the client must send an AT command in order to modify configuration
on the Drone. Send AT command: "AT*CONFIG=\"general:navdata_demo\",\"TRUE\"\\r".
Ack control command, send AT command: "AT*CTRL=0. The drone is now initialized and
sends Navdata demo. This mechanism is summarized by figure 7.1.
How do the client and the drone synchronize ?
The client application can verify that the sequence counter contained in the header structure of
NavData is growing.
There are two cases when the local (client side) sequence counter should be reset :
• the drone does not receive any traffic for more that 50ms; it will then set its ARDRONE_COM_WATCHDOG_MASK
bit in the ardrone_state field (2nd field) of the navdata packet. To exit this mode, the client
must send the AT Command AT*COMWDG.
• The drone does not receive any traffic for more than 2000ms; it will then stop all communication
with the client, and internally set the ARDRONE_COM_LOST_MASK bit in its state
variable. The client must then reinitialize the network communication with the drone.