The on board software is written entirely in C. Non-realtime IPC is done with a TCP server that repeats back any information sent to it. This makes debugging/monitoring/controlling over a network very simple. Realtime data is stored in shared memory.

Note: this is mainly for our reference!

There are 5 major processes:

Forks, controls and handles errors from other processes. This also controls the shared memory,

This process manages the flight (ie, keeps track of when it is ascending/descending/landed, sends text messages etc) and keeps a list of waypoints. The main waypoint tasks:

• Keeping a list of waypoints. Waypoints consist of a position and an optional required altitude.
• Calculating “sub waypoints” for circling around to get to required altitudes etc.
• Calculating when a waypoint is reached based on GPS position and thresholds
• Calculating headings to go in based on the current position and the next waypoint (continuous so it will not drift off course)

Currently for development, there is a very simple waypoint manager that cycles around a set of waypoints in an array.

• Maintaining straight/level flight.
• Calculate current heading
• Bank and turn based on heading to next waypoint and current heading

• Maintain constant airspeed, maybe based on stall speed at current altitude or fixed pitch. Without a pressure sensor, this will have to be done purely with ground speed, so a fixed pitch may be necessary. I shall have to look into attaching a pitot pressure sensor.

Currently for powered flight development, this process is just maintaining a certain altitude.

• Reads GPS data from gpsd using libgps and sticks it in shared memory.

• Calculates roll and pitch attitude (in degrees) from thermopile inputs.

• Various calculations, currently converts two sets of GPS coordinates to bearings and distances.

See client

• Client for server.

• Logs errors and messages.

• Controls servos via i2c.

To display:

• Readings from sensors.
• Flight plan and waypoints
• Attitude/artificial horizon
• Altitude.
• GPS position.
• Speed.
• Rate of descent/ascent.
• Payload status (ascending, descending, landed etc).
• Raw output from log.
• Battery voltages.
• Space remaining on disk.
• Number of photos taken and, depending on bandwidth, a compressed version of the last image.

To send:

• Cut down.
• Take photo.
• Change/add to flight plans.
• Edit/add to waypoints.
• Manual control for emergencies.
• Release parachute.