1. 15 February 2007IASTED Software Engineering 2007, Innsbruck1 Embedded Functional Programming in Hume Gergely Patai patai@iit.bme.hu Péter Hanák hanak@iit.bme.hu Budapest University of Technology and Economics Department of Control Engineering and Information Technology

2. 15 February 2007IASTED Software Engineering 2007, Innsbruck2 Outline  Introducing Hume  Example: lift control  Example: light measurement  Conclusions The Hume language is developed at University of St Andrews and Heriot-Watt University in Scotland within the EmBounded Project (IST-510255). http://www.hume-lang.org http://www.embounded.org

3. 15 February 2007IASTED Software Engineering 2007, Innsbruck3 Hume overview  An experimental functionally based language for embedded systems  Pure functions: no side effects  Inherently parallel  Visual program structure  Static space-time guarantees  Verifiable properties  Increased dependability  Viable on low-end platforms

4. 15 February 2007IASTED Software Engineering 2007, Innsbruck4 Hume example: counter program stream display to "std_out"; type integer = int 32; inc x = x+1; box counter in (n::integer) out (n’::integer, nout::integer) match n -> (inc n, n); wire counter (counter.n’ initially 0) (counter.n, display); Counter display nn’ nout

5. 15 February 2007IASTED Software Engineering 2007, Innsbruck5 Hume basics  Hume programs are ‘boxes’ connected with ‘wires’  Wires:  are mailboxes that can hold one piece of data at a time  each connects strictly one output to one input  statically typed  Boxes:  map their inputs to their outputs with a pure function (combinational network)  the function consists of rules, exactly one of which is chosen by pattern matching on the input  if some outgoing wires needed by the rule are occupied, the result is buffered until the wire is freed up by its consumer  Supersteps: global consume–produce cycles

6. 15 February 2007IASTED Software Engineering 2007, Innsbruck6 Execution alternatives  Source-level interpreter  HAM (Hume Abstract Machine) interpreter  Hume → HAM assembly compilation  Optional transformation to bytecode  Native code  HAM → C conversion (macro expansion)  Compiled with a C compiler, linked to a lightweight runtime system (RTS)  No endianness issues, no malloc, no threads

7. 15 February 2007IASTED Software Engineering 2007, Innsbruck7 Lift control  Task: single-shaft lift simulation  Hardware: mitmót  ARM7 (32-bit) @ 54MHz (Philips LPC2106)  128k flash, 64k RAM  OS: eCos  User code: compiled to native code

8. 15 February 2007IASTED Software Engineering 2007, Innsbruck8 Lift control software Requests state cache →user state’ cache’ C→ C← D→ D← Cabin Door state position →R ←R →D ←D state’ position’ ↑clk R↑ R↓ enabled state ↑C ↓C clk← enabled’ state’

9. 15 February 2007IASTED Software Engineering 2007, Innsbruck9 Light measurement  Task: remote measurement  Hardware: Tmote Sky  MSP430 (16-bit) @ 8MHz  48k flash, 10k RAM  OS: Contiki with HAM interpreter  Stripped string and floating point support  Peripherals accessed as streams  User code: HAM bytecode loadable over the air

10. 15 February 2007IASTED Software Engineering 2007, Innsbruck10 Light measurement software Control Receiver UDP packetCommandAck/Light Speed controlPhoto diode Calibration (thresholds, speeds) State (init/alive/dead) ( Init, _*, _, *) -> (Alive, (200, 400, 50, 10), 50, *) | ( _, _*, _, Reset) -> ( Init, *, *, 0) | ( Dead, _*, _, _*) -> ( Dead, *, *, *) | (Alive, _*, _, Calibrate t1 t2 d1 d2) -> (Alive, (t1, t2, d1, d2), *, 1) | (Alive, (t1, t2, d1, d2), p, *) -> if p < t1 then (Alive, (t1, t2, d1, d2), d1, p) else if p < t2 then (Alive, (t1, t2, d1, d2), d2, p) else (Dead, *, *, *);

11. 15 February 2007IASTED Software Engineering 2007, Innsbruck11 Experiences  Short source code  Easy portability  Big native code (experimental compiler)  No significant speed loss with bytecode  Sufficiently fast for simple tasks  Great potentials for a future IDE

12. 15 February 2007IASTED Software Engineering 2007, Innsbruck12 Future work  Improving the Tmote Sky port of the interpreter  New resource-constrained applications on a variety of platforms  Developing and evaluating extensions and tools for the language  Further information: http://www.inf.bme.hu/fp4es

13. 15 February 2007IASTED Software Engineering 2007, Innsbruck13 Thank you for your attention!