1. Slide 1 School of Engineering Klenke163/MAPLD 2004 An FPSLIC-based UAV Control Platform Robert H. Klenke, Abhishek Handa, Jeffrey E. Quinones, Hung H. (Kevin) Van, Brittiany Wynne Department of Electrical and Computer Engineering Virginia Commonwealth University Richmond, Virginia

2. Slide 2 School of Engineering Klenke163/MAPLD 2004 Outline UAV Goals and System Functions Atmel FPSLIC Device Architecture and Features UAV Flight Control System Architecture UAV Implementation and Testing Conclusions and Future Work

3. Slide 3 School of Engineering Klenke163/MAPLD 2004 UAV System The goal of the project was to develop a flight control system (FCS) for a UAV which would enable it to fly autonomously to GPS waypoints and perform reconnaissance of its overfly area Senior project in computer engineering at VCU  Hardware and software design  Low total system cost  Off-the-shelf hardware system  Available commercial tools for design and implementation Entry in AUVSI Student UAV Competition  High overall system reliability and safety  Reprogrammable for different missions  Simple enough to be completed in less than 6-months Manual mode for takeoff and landing and upset recovery via standard RC controller link Ground station to FCS real-time link for capturing system operating state (debugging) and tuning of flight parameters Real-time video downlink for reconnaissance mission System was good enough to place first in the 2 nd Annual AUVSI Student UAV Competition – all other teams used COTS UAV autopilots

4. Slide 4 School of Engineering Klenke163/MAPLD 2004 ATMEL FPSLIC Device Characteristics 8-bit AVR microcontroller, EPROM (program memory), SRAM (data memory), 40K gate FPGA on a single device Some of the I/O ports on the AVR are connected to package pins, and others are connected to the I/O’s of the FPGA External interrupts to the AVR can come from the outside world via a dedicated package pin, or from the FPGA via a built-in interrupt controller connected to FPGA I/O’s Some of the FPGA I/O’s are connected to package pins to interface to the outside world The AVR contains a dedicated register connected to I/O selection logic that can be used to select and communicate with several different user designed peripherals implemented in the FPGA. Atmel has designed an integrated hardware/software codesign and coverification environment to develop FPSLIC applications Atmel has available a low-cost FPSLIC-based development board that integrates the device with a number of useful parts such as a power regulator, RS-232 connectors, I/O headers, at 15-segment display, etc.

5. Slide 5 School of Engineering Klenke163/MAPLD 2004 Atmel FPSLIC Hardware Architecture

6. Slide 6 School of Engineering Klenke163/MAPLD 2004 Atmel FPSLIC Development Environment HW Design Flow SW Design Flow Simulation-based Coverification Flow

7. Slide 7 School of Engineering Klenke163/MAPLD 2004 Reasons for Selection of ATMEL Device Low-cost COTS system that is readily available Fairly powerful integrated hardware/software system 40K gate FPGA is easily large enough to implement the hardware required for this application Program and data memory are built-in and, although not large, have proven adequate for this application Typical microcontroller resources and peripherals are provided  RS-232 ports, interrupt pins, timers and counters, etc. Small size, weight, and power consumption due to single integrated device Proven, easy-to-use, integrated development environment for both hardware AND software available

8. Slide 8 School of Engineering Klenke163/MAPLD 2004 System Architecture Overview Video monitor or PC-based video capture system Real-time video stream FCS status data FCS parameter change commands Manual RC control commands 72 MHz 900 MHz 2.4 GHz Visual Basic PC-based ground control system Manual RC pilot

9. Slide 9 School of Engineering Klenke163/MAPLD 2004 UAV System Hardware Architecture

10. Slide 10 School of Engineering Klenke163/MAPLD 2004 UAV Functions Manual RC pilot is responsible for performing takeoffs and landings and switching FCS from manual to autonomous mode Commercial off-the-shelf, Infrared-based horizon sensor is used in autonomous mode to perform pitch and roll stabilization This gives the FCS a stable platform that it can “steer” around the sky using GPS positioning FCS must perform the following functions: Decode the servo positioning pulses being received from the RC pilot via the RC receiver  Detect manual vs. autonomous mode via the position of one of the channels  In manual mode, transfer (generate) the positioning pulses to the servos exactly as received from the RC pilot Receive position (LLA), and velocity (ENU) information from the GPS  RS-232 serial data via TSIP (Trimble Standard Interface Protocol) at 1- second intervals

11. Slide 11 School of Engineering Klenke163/MAPLD 2004 UAV Functions (cont.) Determine aircraft position and velocity vs. desired track to next waypoint Determine correct aircraft steering commands to retain/regain desired track Generate required pulses for servos based on aircraft mode and commanded surface positions Detect waypoint arrival and update next waypoint based on mission data Provide system state to ground station via radio modem link Receive, decode, and implement parameter update commands from ground station Detect loss-of-signal from RC transmitter and take appropriate action depending on system state (failsafe) In manual mode, spiral aircraft to the ground in a low energy state In autonomous mode, fly to first (home) waypoint and wait for signal from RC transmitter

12. Slide 12 School of Engineering Klenke163/MAPLD 2004 UAV Hardware/Software Partitioning Characteristics of functions that are more efficiently implemented in hardware: Simple, repetitive functions – I.e., monitoring system inputs to insure they remain within a desired range Functions that do not fit well within the processor’s time scale  Repetitive computations that tax the processor’s resources, OR,  Functions whose time scale is much longer than the processor’s cycle time In the UAV system, that includes: Decoding the servo positioning pulses being received from the RC pilot via the RC receiver Generating the required pulses for servos based on aircraft mode and commanded surface positions Detecting loss-of-signal from the RC transmitter Servo position controlled by pulse width of 0.5 ms to 2.5 ms Pulses (regardless of size) must repeat at 10 ms intervals

13. Slide 13 School of Engineering Klenke163/MAPLD 2004 UAV Flight Control System (FCS) Hardware Architecture AVR Microcontroller Register File Down-counter based PWM Generators Control State Machine 10ms Timer On-Chip FPGA 16 Aircraft Servos Aircraft FM Receiver Register File 16 Counter-based pulse width measurement system Atmel FPSLIC Device UART connections to GPS Receiver and 900 MHz link to GCS Main FCS software for aircraft stabilization and waypoint following

14. Slide 14 School of Engineering Klenke163/MAPLD 2004 FSC Software Function Example

15. Slide 15 School of Engineering Klenke163/MAPLD 2004 UAV Flight Control System (FCS)

16. Slide 16 School of Engineering Klenke163/MAPLD 2004 FCS Testbed

17. Slide 17 School of Engineering Klenke163/MAPLD 2004 UAV Aircraft

18. Slide 18 School of Engineering Klenke163/MAPLD 2004 Ground Station Display Lat: 37.0156 Lon: -76.13 Heading: 50 Alt: 98

19. Slide 19 School of Engineering Klenke163/MAPLD 2004 Lessons Learned Hardware resources in the FPGA were more than adequate for this application Application used about 30% of the total 40K gate size I/O select logic built into the AVR FPGA interface was used, but the dedicated interrupt structure was not The hardware development flow and tools were easy to use and gave very few problems Leonardo synthesis, Modelsim simulation, and Figaro place and route were all familiar and worked as expected The compiler was an active participant in the software development… Certain C++ constructs would not compile, or produced erroneous results Memory management issues produced unwanted, and sometime unpredictable side effects, requiring “padding” of the code to produce correct operation The cosimulation tools were not as effective for this application as we had hoped Steep learning curve hindered use in the beginning, and… Lack of simulation models for other system components (e.g., GPS receiver RS-232 interface) and slow system simulation hindered use as the software became more complex The FPSLIC device itself worked very well, but available memory size was an issue Available RAM was adequate, but we were very careful to minimize use  conversion of GPS coordinates from floats to integers  use of position relative to local datum vs. absolute position  “flat earth” assumption Available program ROM was ultimately too small for current system and will significantly limit future system growth

20. Slide 20 School of Engineering Klenke163/MAPLD 2004 Conclusions and Future Work System has been fully developed and tested Flight testing took place at Felker Army Airfield at Ft. Eustis in VA under their UAV development efforts Some interest in further development of this system has been generated because of its low cost Future improvements to the system architecture are being considered: The use of a gyro unit and additional software to provide wing leveling in lieu of the commercial infrared-based CoPilot unit Addition of pressure sensors for altitude and airspeed measurement to allow more precise control More sophisticated, linear PID algorithms for altitude and heading control Migration of the FCS to a Xilinx Microblaze-based implementation is also being considered: Faster, more powerful 32-bit processor More flexibility in changing/adding to system architecture Toolset more difficult to use Problems such as adding off-chip memory for data and storage to a Microblaze-based system must be addressed

21. Slide 21 School of Engineering Klenke163/MAPLD 2004 AUVSI Competition