Architectures and Applications for Wireless Sensor Networks ( ) Node Programming Models Chaiporn Jaikaeo Department of Computer Engineering Kasetsart University

2 Outline Microcontroller programming Microcontroller programming  Software development cycle Hardware abstraction Hardware abstraction Event-driven programming model Event-driven programming model  TinyOS Multithreaded programming model Multithreaded programming model  Contiki

3 IWING-MRF Mote Radio transceiver 8-bit AVR Microcontroller USB Connector (for reprogramming and power) Analog/Digital sensor connectors External battery connector UART connectors Morakot Saravanee, Chaiporn Jaikaeo, Intelligent Wireless Network Group (IWING), KU

4 Microcontroller flash memory BSL Typical Development Process For microcontrollers with bootstrap loader (BSL) installed For microcontrollers with bootstrap loader (BSL) installed Source code (C/Asm) Cross Compiler/Assembler Machine code Serial/USB

5 Build Simple App Let's build a simple application Let's build a simple application How to know whether our program is running? How to know whether our program is running?  Make mote output something  What can be used as output?

6 IWING-MRF Schematic Available on course's homepage Available on course's homepage

7 IWING-MRF – Blinking LED Task: turn a LED on and off repeatedly Task: turn a LED on and off repeatedly Idea Idea  Configure Port D's Pin 5 (PD5) for output  Repeatedly set the pin logic level to 0 and 1  Add some delay before toggling pin level

8 IWING-MRF C Code – blink.c How to add delay? How to add delay? Can the code be made shorter? Can the code be made shorter? #include main() { DDRD |= (1 << 5); // Make PD5 output while (1) { // Set pin logic to low PORTD &= ~(1 << 5); // Add some delay // Set pin logic to high PORTD |= (1 << 5); }

9 Compiling Make an ELF binary by running cross compiler Make an ELF binary by running cross compiler Note: blink.elf is not a Windows or Linux executable! Translate the object file into ihex format Translate the object file into ihex format $ avr-gcc -mmcu=atmega328p –o blink.elf blink.c $ avr-objcopy -j.text -j.data –O ihex blink.elf blink.hex

10 Flashing Code Into Mote Plug mote into a USB port Plug mote into a USB port Activate boot-loader Activate boot-loader  Press and release RESET while holding USER/B.L. Make sure it is recognized by your PC Make sure it is recognized by your PC Invoke chip programmer Invoke chip programmer $ avrdude -p atmega328p -c usbasp -U flash:w:blink.hex $ lsusb Bus 003 Device 049: ID 16c0:05dc VOTI Bus 001 Device 003: ID 046d:c03d Logitech, Inc.ls

11 IWING-MRF's Boot Loader

12 IWING's MoteLib Software Hardware Morakot Saravanee, Patra Poome, Chaiporn Jaikaeo, Intelligent Wireless Network Group (IWING), KU

13 Hardware Abstraction IWING-MRF Hardware IWING-MRF API Implementation

14 Mote and Network Emulator Virtual Mote

15 Event-Driven Programming Model MoteLib and TinyOS provides event-based programming environment MoteLib and TinyOS provides event-based programming environment Idle loop Radio event handlerSensor event handlerTimer event handler Boot event handler Handled by Kernel Handled by developer

16 Example Turn red LED on and off repeatedly every 500 ms Turn red LED on and off repeatedly every 500 ms #include Timer t; void fired() { ledToggle(0); } void boot() { timerCreate(&t); timerStart(&t, TIMER_PERIODIC, 500, fired); }

PORTB PORTC PORTD Practicum Board CPE, KU ResetPower Concurrency Example: press and release SW1 to toggle LED1 Example: press and release SW1 to toggle LED1  USB must still be operational by calling usbPoll() at least every 50 ms 17 SW1LED1

Failed Attempt 18 void checkSwitch() { while (!IS_PUSHED(SW1)) while (!IS_PUSHED(SW1)) ; while (IS_PUSHED(SW1)) while (IS_PUSHED(SW1)) ; toggle(LED1); toggle(LED1);} int main() { for (;;) for (;;) { usbPoll(); usbPoll(); checkSwitch(); checkSwitch(); }} Blocking Blocking

Finite State Machines (FSM) To allow concurrent tasks, each task is typically implemented using a Finite State Machine (FSM) To allow concurrent tasks, each task is typically implemented using a Finite State Machine (FSM) 19 Released Pushed SW1 pushed SW1 released / Toggle LED int state; int main() { state = RELEASED; state = RELEASED; for (;;) { for (;;) { usbPoll(); usbPoll(); checkSwitch(); checkSwitch(); }} void checkSwitch() { if (state == RELEASED) { if (state == RELEASED) { if (IS_PRESSED(SW1)) { if (IS_PRESSED(SW1)) { state = PUSHED; state = PUSHED; } } if (state == PUSHED) { if (state == PUSHED) { if (!IS_PRESSED(SW1)) { if (!IS_PRESSED(SW1)) { state = RELEASED; state = RELEASED; toggle(LED1); toggle(LED1); } }}

20 Creating a Reading Task Event-based code can be difficult to read and maintain Event-based code can be difficult to read and maintain Idea Idea  Make a reading task that runs forever  Other tasks can also be added to run concurrently Start timer Wait until timer expired Create timer Turn on sensors Request reading Wait until data ready Complete 4 samples? Compute and display average Turn off sensors

Problem with Event-based Model Threads: sequential code flowEvents: unstructured code flow Very much like programming with GOTOs 21

Events Require One Stack Four event handlers, one stack Four event handlers, one stack Eventhandler 1Eventhandler 2Eventhandler 3 Stack is reused for every event handler Eventhandler 4 22

Problem with Multithreading Four threads, each with its own stack Four threads, each with its own stack Thread 1Thread 2Thread 3Thread 4 23

24 Emulating Concurrency Previous example wouldn't work because of the blocking while-loop Previous example wouldn't work because of the blocking while-loop  Other parts of the system will be unresponsive Must return to kernel inside of the while- loops Must return to kernel inside of the while- loops During kernel's idle loop, keep jumping into the while-loops During kernel's idle loop, keep jumping into the while-loops

Coroutines Generalized subroutines Generalized subroutines  Allow multiple entry points for suspending and resuming execution at certain locations Can be used to implement: Can be used to implement:  Cooperative multitasking  Actor model of concurrency 25

Routine 2 Subroutines vs. Coroutines Routine 1 Subroutines Routine 2 Routine 1 Coroutines call call return return yieldyield yield yield 26 “Subroutines are a special case of coroutines.” --Donald Knuth Fundamental Algorithms. The Art of Computer Programming Fundamental Algorithms. The Art of Computer Programming

27 Programming Model Kernel's Idle loop Task 2 Event handler2 Task 1 Event handler1 Handled by Kernel Handled by developer call return call return continue yield yield continue

Implementing Continuation Each coroutine must be able to continue from where it last yielded Each coroutine must be able to continue from where it last yielded Routine 1 28 Main Loop continue yield continue yield

29 Duff's Device Invented to optimize data transfer by means of loop unwinding Invented to optimize data transfer by means of loop unwinding Switch cases are used like GOTO labels Switch cases are used like GOTO labels do { *to = *from++; } while(--count > 0); register n = (count + 7) / 8; switch(count % 8) { case 0: do { *to = *from++; case 7: *to = *from++; case 6: *to = *from++; case 5: *to = *from++; case 4: *to = *from++; case 3: *to = *from++; case 2: *to = *from++; case 1: *to = *from++; } while(--n > 0); }

30 Protothreads Invented by Adam Dunkels and Oliver Schmidt Invented by Adam Dunkels and Oliver Schmidt  Used in the Contiki OS Provides light-weight mechanism for concurrent programming using standard C macros and switch-case statements Provides light-weight mechanism for concurrent programming using standard C macros and switch-case statements Heavily inspired by Duff's Device and Simon Tatham's Coroutines in C Heavily inspired by Duff's Device and Simon Tatham's Coroutines in CCoroutines in CCoroutines in C See See 

Protothreads Protothreads require only one stack Protothreads require only one stack E.g, four protothreads, each with its own stack E.g, four protothreads, each with its own stack Events require one stack Protothread 1 Protothread 2Protothread 3Protothread 4 Just like events 31

Six-line implementation Protothreads implemented using the C switch statement Protothreads implemented using the C switch statement Heavily inspired by Duff's Device and Simon Tatham's Coroutines in C Heavily inspired by Duff's Device and Simon Tatham's Coroutines in CCoroutines in CCoroutines in C struct pt { unsigned short lc; }; #define PT_INIT(pt) pt->lc = 0 #define PT_BEGIN(pt) switch(pt->lc) { case 0: #define PT_EXIT(pt) pt->lc = 0; return 2 #define PT_WAIT_UNTIL(pt, c) pt->lc = __LINE__; case __LINE__: \ if(!(c)) return 0 if(!(c)) return 0 #define PT_END(pt) } pt->lc = 0; return 1 32

33 Protothreads Limitations Local variables must be manually preserved Local variables must be manually preserved  Local variables are created on stack  They are destroyed when function returns  So they should be stored in an explicit state object  Or declared static, if reentrancy is not required switch-case statements are not allowed switch-case statements are not allowed Cannot take advantage of multi-processing Cannot take advantage of multi-processing

Contiki OS Scheduler 34