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6LoWPAN: The Wireless Embedded Internet
Companion Exercise Slides
Zach Shelby, Martti Huttunen
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Figures on slides with book symbol from 6LoWPAN: The Wireless Embedded
Internet, Shelby & Bormann, ISBN: 978-0-470-74799-5, (c) 2009 John Wiley & Sons
Ltd
The Book
6LoWPAN: The Wireless Embedded
Internet
by Zach Shelby, Carsten Bormann
Length: 254 pages
Publisher: John Wiley & Sons
http://www.6lowpan.net
Companion web-site with blog, full
companion course slides and
exercises
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Outline
•
•
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•
•
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Introduction
Embedded Devices
Operating Systems
Embedded Development
6LoWPAN Implementation Issues
Exercise Hardware
Contiki & uIP
Exercises
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Introduction
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Embedded Meets Wireless
• Microcontrollers are everywhere in embedded systems
– appliances, watches, toys, cameras, industrial control, mobile phones,
sensors, cars, automation
• Microcontroller vs. microprocessor market
– 15 x more microcontroller units sold yearly (8 billion)
– 20 billion vs 43 billion USD market by 2009
• Possibilities of wireless are endless
– 802.15.4 chips to 150 million unit sales by 2009
• Embedded systems have special characteristics
• Academic community very computer science and protocol driven,
often ignoring
– Physical layer realities
– Embedded system operation
– Real-time capabilities
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Embedded Devices
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Device Architecture
• Microcontroller and program code
• Power supply
– Power management
– Renewable energy?
•
•
•
•
•
•
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Memory (RAM, FLASH)
Sensors
Actuators
Communication
Input/output
Part of a larger system?
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Microcontroller
• Main processing units of embedded devices
• Special purpose and highly integrated
– Integrated RAM, ROM, I/O, peripherals
– Extremely good power to performance ratio
– Cheap, typically 0.25 - 10.00 USD
• Executes programs including embedded system control,
measurement & communications
– Usually time-critical requiring guarantees
– Real-time performance a common requirement
• Pre-emptive scheduled tasks
• Queues and semaphores
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Example: MSP430
• Texas Instruments mixedsignal uC
• 16-bit RISC
• ROM: 1-60 kB
• RAM: Up to 10 kB
• Analogue
– 12 bit ADC & DAC
– LCD driver
• Digital
– USART x 2
– DMA controller
– Timers
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Example: Atmel AVR
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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•
•
•
•
Atmel AVR family
8-bit RISC
RAM: Up to 4 kB
ROM: Up to 128 kB
Analogue
– ADC
– PWM
• Digital
– USARTs
– Timers
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Memory
• Random access memory (RAM)
– Included on-board in microcontrollers
– Often the most valuable resource
• Read-only memory (ROM)
– Usually actually implemented with NOR flash memory
• Flash
–
–
–
–
Eraseable programmable memory
Can be read/written in blocks
Slow during the write process
Consumes power of course!
• External memory
– External memory supported by some microcontrollers
– Serial flash always supported
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Common Bus Interfaces
• Digital and analogue I/O
– Accessed by port and pin number (e.g. P1.3)
– Some pins are also connected to interrupts
• UART
– Asynchronous serial bus
– After level translation it is an RS232 bus
– Usually kbps up to 1 mbps
• SPI (serial peripheral interface)
– Synchronous serial bus
– Reliable with speeds of several Mbps
• I2C (inter-integrated circuit) bus
– 2-wire bus with data and clock
• Parallel bus
– Implemented with X-bit width
– X-bit address and clock signals
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Communications
• Embedded devices are autonomous but most often part of a
larger system
• Thus communications interfaces are very important in the
embedded world
• Wired interfaces
– Serial: RS232, RS485
– LAN: Ethernet
– Industrial: Modbus, Profibus, Lontalk, CAN
• Wireless interfaces
– Low-power: IEEE 802.15.4 (ZigBee, ISA100, Wireless HART)
– WLAN: WiFi
– WAN: GPRS, WiMax
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Transceivers
• Modern embedded communications chips are transceivers: they
combine half-duplex transmission and reception.
• Transceivers integrate varying functionality, from a bare analogue
interface to the whole digital baseband and key MAC functions.
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Important Characteristics
• Level of digital integration
• Power consumption and efficiency
– Transition speeds and consumption
– Levels of sleep
•
•
•
•
•
•
•
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Carrier frequency and data rate
Modulation
Error coding capabilities
Noise figure and receiver sensitivity
Received signal strength indicator (RSSI)
Support for upper layers
Data and control interface characteristics
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Example: RFM TR1000
•
•
•
•
•
•
Proprietary radio at 916 MHz
OOK and ASK modulation
30 kbps (OOK) or 115.2 kbps (ASK) operation
Signal strength indicator
Sleep
Provides bit interface
0.7 uA
Not included:
–
–
–
–
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Tx
Rx
12 mA
3.8 mA
Synchronization
Framing
Encoding
Decoding
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Example: CC2420
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•
•
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IEEE 802.15.4 compliant radio
2.4 GHz band using DSSS at 250 kbps
Integrated voltage regulator
Integrated digital baseband and MAC functions
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Clear channel assessment
Energy detection (RSSI)
Synchronization
Framing
Encryption/authentication
Retransmission (CSMA)
Sleep
Idle
Tx
Rx
20 uA
426 uA
8.5 – 17.4 mA
18.8 mA
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Example: CC2430
• System-on-a-chip solution
• Integrated 8051 microcontroller
– 32 MHz Clock Speed
– ADC, DAC, IOs, 2 UARTs etc.
– 8 kB of RAM, up to 128 kB of ROM
• Integrated IEEE 802.15.4 radio, like the CC2420
• Power consumption 10-12 mA higher than the CC2420,
coming from the 8051 microcontroller
• Saves cost, only about 1 EUR more expensive than the
CC2420
• Internal DMA makes radio and UART performance better than
with a uC + CC2420 solution
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Power Consumption
• Radio power consumption critical
to consider
• Power output level
– Limited savings effect
– Optimal power difficult
– Must be considered globally
Output
Power (mW)
0.003
0.032
0.100
0.200
0.316
0.501
0.794
1.000
Power
Used (mW)
15.30
17.82
20.16
22.50
25.02
27.36
29.70
31.32
• Transition times
– Each transition costs
– Power equal to RX mode
– Should be accounted for
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Power Consumption
A simple approximation for power consumption:
1
Pavg  PRxTwk  up  PRx ( N TxTTx  up  N RxTRx up )  PTxTTx  PRxTRx  PidleTidle  PsleepTsleep
TF
















Twk  up =
TTx  up =
T
=
Tx
TRx up =
TRx
Tidle
Tsleep
N Tx
N Rx
TF
PTx
PRx
Pidle
Psleep
Pavg
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Time that takes to go from sleep state to awake state
Transmitter setup time, i.e. time it takes for the transmitter to be ready
Time in the Tx state
Receiver setup time, i.e. time it takes for the receiver to be ready
= Time in the Rx state
= Time in the idle state
= Time in the sleep state
= Average number of times per frame that the transmitter is used
= Average number of times per frame that the receiver is used
= Duration of the time frame
= Power used in the Tx state
= Power used in the Rx state
= Power used in the idle state
= Power used in the sleep state
= Average power used by the transceiver
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Sensors & Actuators
• Sensors measure real-world phenomena and convert them to
electrical form
– Analogue sensors require an ADC
– Digital sensors use e.g. I2C or SPI interfaces
– Human interface can also be a sensor (button)
• IEEE 1451 standard becoming important
– Defines standard interfaces and auto-configuration
– Also some protocol specifications
• Actuators convert an electrical signal to some action
– Analogue and digital interfaces both common
– A motor servo is a good example
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Operating Systems
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Real-time Operating Systems
• Library vs. operating system
– Operating system manages all resources
• Embedded systems have pre-defined tasks
– Designed to optimize size, cost, efficiency etc.
• Real-time
– Real-time OS provides tools to meet deadlines
– Pre-emptive, queues, semaphores
• Concurrency
– Execution flows (tasks) able to run simultaneously
– Threads and processes
• Sockets and APIs
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Real-time Issues
• Wireless embedded systems usually are real-time
– Watch, robot, building sensor, control node
• A RTOS only facilitates real-time system creation
– Still requires correct software development
• RTOS is not necessarily high performance
– Can meet general system deadlines (soft real-time)
– or deterministically (hard real-time)
• Deadlines can be met using
– Specialized pre-emptive scheduling algorithms
– Proper inter-task design & communication
– Semaphores and queues to avoid racing
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Real-time Issues
Task1
Task2
Task3
Unlock
resource A
Lock
resource A
Task1
T1
T2
TN
Task2
Task1
Task3
Task2
Task3
T1
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T2
Try access
resource A
time
TN
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Concurrency
• Concurrency occurs when two or more execution flows run
simultaneously
• It introduces many problems such as
– Race conditions from shared resources
– Deadlock and starvation
• OS needs to coordinate between tasks
– Data exchange, memory, execution, resources
• There are two main techniques
– Process based
• CPU time split between execution tasks
• Embedded systems typically use lighter threads
– Event based
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Concurrency
• Process based
• Event based
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OS Examples
• Example embedded operating systems
–
–
–
–
Contiki (www.sics.se/~adam/contiki)
FreeRTOS (www.freertos.org)
TinyOS (www.tinyos.org)
and thousands of others...
• For higher powered MCUs (e.g. ARMs)
–
–
–
–
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VX Works
Microcontroller Linux (Android, Maemo etc.)
Windows CE
Symbian
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Embedded Development
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Embedded Development
Objects
Sources
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Compiler
Binary
Linker
Programmer
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Embedded Development
• Software resides in system non-volatile memory
– External or internal flash/eeprom/prom memories
– Modern microcontrollers are capable of writing the internal flash
memory run-time and often do not have an external memory bus
• Development is done outside the system
• Cross-compilers are used to create binary files
– Cross-compiler creates binary files for a different architecture than
it is running on
– Various commercial and free compilers available
• System is programmed by uploading the binary
– In-system programming tools or external flashers
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Cross-compiler Environments
• Integrated development environments (IDEs)
– Commercial compilers are usually of this type
– Usually dependent on a specific OS (Windows)
– Integrate a text editor, compiler tools and project management
along with C library
– System programmer tool usually tightly integrated
– Also open-source IDEs available
• Open-source IDEs usually employ “plugin” architecture
• General-purpose extensible environments
• Include scripting tools for running any command line tools: compilers,
linkers, external editors and programmers
• Example: Eclipse (implemented in Java)
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Cross-compiler Environments
• Command line utilities
– Separate compiler/linker, editor and project management tools,
architecture-dependent C library
• Project management: make
– make is an automated software building tool
– Based on target-dependency-operation style blocks
– Allows use of project templates and separate platform build rules
by using “include files”
– Most common way of managing open-source software projects
– automake and autoconf tools extend functionality to platformindependent software development
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Cross-compiler Environments
• Command line compilers
– most common is gcc: available for a multitude of microcontroller
and -processor architectures
– sdcc: Small Device C Compiler: PICs, 8051's etc.
– single-architecture compilers
• System programming tools
– usually specific to a single microcontroller family
– vary greatly in their ease of use and interface type
– most require some sort of programming cable or a programmer
device to upload software
– dependent on the microcontroller programming algorithm
• standard buses (SPI, UART, JTAG) vs. proprietary buses
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Cross-compiler Environments
• Command-line tools vs. (commercial) IDEs
– IDEs are easily accessible: single installer, single GUI
– Commercial IDEs vary greatly in usability, standards compliance
and are (usually) tied to a single architecture -> bad portability
– Most commercial IDEs don't really support templates
• Programmer must go through various dialogs to create a new project
• Often project files can not just be copied (contain directory paths and
such) and may be binary format
– Command line tools have a steeper learning curve
• Once learned, applicable to most architectures
• Higher flexibility and ease of duplicating projects
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Cross-compiler Issues
• Portability
– Header files may not follow standard naming
– Hardware-specific header files might not be automatically selected
• Most commercial IDEs use different names for each different
hardware model -> difficulties in portability
• gcc e.g. uses internal macros for model selection -> easier portability
via environment variables, no header changes
• Hardware register access and interrupt handlers
– Interrupt handler declaration is compiler-dependent
• Declaration format is not standardized
• Can be worked around via macros (in most cases)
– Some compilers (and C libraries) require I/O macros
• gcc ports implement direct register access modes
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Open-source Tools
• Various text editors available: nedit, emacs, vi ...
• Project build system: make
• Compilers/linkers: binutils & gcc, sdcc
– binutils: as, ld, objcopy, size etc.
– gcc: c compiler; uses binutils to create binary files
• Standard C libraries
– Provide necessary development headers and object files for
linking and memory mapping
– msp430-libc for MSP430, avr-libc for AVR
• Programmers
– AVR: uisp, avrdude
– MSP430: msp430-bsl, msp430-jtag
– CC2430: nano_programmer
• IDE: Eclipse
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SDCC Compiler
• Simple Device C Compiler
• http://www.sdcc.org
• Specialized in 8051, PIC, HC08 etc. microcontrollers
– Has CC2430 and CC2510 support
•
•
•
•
sdcc application handles both compilation and linking
Uses make build environment
Compatible with Eclipse
Support for banking (needed in 8051 with 64k+ ROM)
– Thanks to Peter Kuhar for banking support
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6LoWPAN Implementation Issues
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Chip Models
• How to integrate 6LoPWAN into an embedded device?
• Challenges:
–
–
–
–
Lack of standard interfaces (no USB or PCMCIA)
No standard operating systems (if any!)
Power consumption limitations
Price limitations
• Models for integrating 6LoWPAN include SoC, two-chip or network
processor
• System-on-a-chip model
– Everything on one chip
+ Maximum integration
+ Minimum price and size
- Longer, more difficult development
- Little if any portability
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Chip Models
• Two-chip solution
– Separate radio transceiver
+ Free choice of uC
+ More portability
- More expensive
- App integration with stack
• Network processor solution
– Network stack on the radio
+ Free choice of uC
+ Application independent of
the stack
+ Easy integration
- More expensive
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Contiki uIPv6
• Popular embedded OS for small microcontrollers
– MSP430, AVR, PIC, 8051 etc.
•
•
•
•
•
http://www.sics.se/contiki
Standard C-based
Portable applications
Lightweight protothreads
uIPv6 Stack
– Full IPv6 support
– RFC4944 + 6lowpan-hc
– UDP, TCP, ICMPv6
• Great for research
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NanoStack 2.0
• Sensinode’s commercial 6LoWPAN stack
• Network processor model
– NAP interface over UART
• Optimized for SoC radios
– TI CC2430, CC2530
– TI CC1110
– Portable
•
IPv6/6LoWPAN stack
–
–
–
–
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UDP, ICMPv6
RFC4944, 6lowpan-hc
6lowpan-nd
NanoMesh IP routing
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Router Integration
• Edge Routers interconnect the
IPv6 world and 6LoWPAN
• An ER needs to implement:
–
–
–
–
6LoWPAN interface(s)
6LoWPAN adaptation
Simple 6LoWPAN-ND
A full IPv6 protocol stack
• Other typical features include:
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–
–
–
–
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IPv4 support and tunneling
Application proxy techniques
Extended LoWPAN support
A firewall
Management
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Example Exercise Hardware
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Exercise Hardware
• NanoRouter USB 2.4GHz
– Serial USB device
– NanoStack 2.0
– High-power amplifier
• NanoSensor 2.4GHz
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–
–
–
–
Demo sensor node
Rechargeable batteries
3-axis accelerometer
Light sensor
D-connector for external sensors
• Support for either NanoStack or Contiki
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NanoSensor D-connector
• Standard 9-pin D-connector for sensor expansion
• D-connector pin-out:
1 = 3.3V in/out
2 = Digital I/O or programmer connection
3 = Analog switch control. 1=external I/O in use
4 = Reset
5 = Ground
6 = A/D (Digital I/O). P0_0
7 = Digital I/O (P2_1) or programming connection
8 = UART out (from RC module)
9 = UART in (to RC module)
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Contiki
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What is Contiki?
•
Contiki is an open-source operating system/protocol stack for
embedded systems
•
Highly portable and reasonably compact
•
Protocol stack configuration customizable
•
Originally created by Adam Dunkels, developer of the uIP
stack
•
http://www.sics.se/contiki
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Contiki processes
•
Contiki core is event-driven
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–
–
–
•
Interrupts and HW drivers generate events
Events are dispatched to event handlers by the Contiki core
Event handlers must return control to core as soon as possible
Co-operative multitasking
Basic processes are implemented using protothreads
– Easier to create sequential operations
– An abstraction to avoid complex state-machine programming
• In more complex applications, the amount of states may be huge
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Contiki execution models
•
Contiki offers multiple execution models
•
Protothreads: thread-like event handlers
– Allow thread-like structures without the requirement of additional
stacks
– Limits process structure: no switch/case structures allowed
– May not use local variables
•
Multi-threading model available
– For more powerful systems
– Allows structured application design
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Contiki processes
•
Contiki core is event-driven
–
–
–
–
•
Interrupts and HW drivers generate events
Events are dispatched to event handlers by the Contiki core
Event handlers must return control to core as soon as possible
Co-operative multitasking
Basic processes are implemented using protothreads
– Easier to create sequential operations
– An abstraction to avoid complex state-machine programming
• In more complex applications, the amount of states may be huge
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Contiki processes: An example
/* Declare the process */
PROCESS(hello_world_process, “Hello world”);
/* Make the process start when the module is loaded */
AUTOSTART_PROCESSES(&hello_world_process);
/* Define the process code */
PROCESS_THREAD(hello_world_process, ev, data) {
PROCESS_BEGIN();
/* Must always come first */
printf(“Hello, world!\n”);
/* Initialization code goes here */
while(1) {
/* Loop for ever */
PROCESS_WAIT_EVENT();
/* Wait for something to happen */
}
PROCESS_END();
/* Must always come last */
}
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Contiki processes: Notes
•
A process may not use switch-case constructs
– A limitation of the protothread model
– Complex state structures and switches should be subroutines
•
A process may not declare local variables
– Variables will lose their values at any event waiting call
– All variables required by the main process must be static
•
Effects on application design
– The main process thread should only contain sequences between event
waits
– All operations should be done in subroutines
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Contiki events
•
process_post(&process, eventno, evdata);
– Process will be invoked later
•
process_post_synch(&process, evno, evdata);
– Process will be invoked now
– Must not be called from an interrupt (device driver)
•
process_poll(&process);
– Sends a PROCESS_EVENT_POLL event to the process
– Can be called from an interrupt
•
Using events
PROCESS_THREAD(rf_test_process, ev, data) {
while(1) {
PROCESS_WAIT_EVENT();
if (ev == EVENT_PRINT) printf(“%s”, data);
}
}
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Contiki timers
•
•
Contiki has two main timer types; etimer and rtimer
Etimer: generates timed events
Declarations:
static struct etimer et;
In main process:
while(1) {
etimer_set(&et, CLOCK_SECOND);
PROCESS_WAIT_EVENT_UNTIL(etimer_expired(&et));
etimer_reset(&et);
}
•
Rtimer: uses callback function
– Callback executed after specified time
rtimer_set(&rt, time, 0 , &callback_function, void *argument);
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Contiki Protocol Stacks
•
Contiki has 2 different protocol stacks: uIP and Rime
•
uIP provides a full TCP/IP stack
–
–
–
–
•
For interfaces that allow protocol overhead
Ethernet devices
Serial line IP
Includes IPv4 and IPv6/6LoWPAN support
Rime provides compressed header support
– Application may use MAC layer only
•
Protocol stacks may be interconnected
– uIP data can be transmitted over Rime and vice versa
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The Rime protocol stack
•
Separate modules for protocol parsing and state machines
– Rime contains the protocol operation modules
– Chameleon contains protocol parsing modules
•
Rime startup: an example
– Configure Rime to use sicslowmac over cc2430 rf
– Startup is done in platform main function:
platform/sensinode/contiki-sensinode-main.c
rime_init(sicslowmac_init(&cc2430_rf_driver));
set_rime_addr(); //this function reads MAC from flash and places
//it to Rime address
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Rime: Receiving
•
Setting up Rime receiving: broadcast
– Set up a callback function
Declarations:
static struct broadcast_conn bc;
static const struct broadcast_callbacks broadcast_callbacks =
{recv_bc};
The callback definition:
static void
recv_bc(struct broadcast_conn *c, rimeaddr_t *from);
In main process:
broadcast_open(&bc, 128, &broadcast_callbacks);
•
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Unicast receive in a similar manner
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Rime: Sending
•
Sending broadcast data using Rime
Declarations:
static struct broadcast_conn bc;
In main process:
packetbuf_copyfrom("Hello everyone", 14);
broadcast_send(&bc);
•
Sending unicast data using Rime
Declarations:
static struct unicast_conn uc;
In your function:
rimeaddr_t *addr;
addr.u8[0] = first_address_byte;
addr.u8[1] = second_address_byte;
packetbuf_copyfrom("Hello you", 9);
unicast_send(&uc, &addr);
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Creating Contiki Ports
•
First step: see if your cpu already has code
– If yes, configure your platform to use it
– If not, see other cpu directories for implementation models
•
Second step: see if your hardware is close to other platforms
– If yes, copy code from example platform and modify
– If not, see other platforms for minimal model
•
Create a test application
– Start with LEDs in platform/myplatform/contiki-myplatform-main.c
– Use for loops to make sure that your compiler works
– Continue by adding printf's to see if your UART works
•
First real application
– Create an etimer for your test process: flash LEDs, print info
– Try different timeouts to see if your clocks are correct
•
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Add more drivers and try them out
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Exercises
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Contiki Basics
•
Create your own Contiki “Hello World” application using
/examples/sensinode as an example. Compile and run it on
the CC2430 target platform
•
Create two parallel Contiki processes, each controlling a
different LED
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Contiki Advanced
•
Use an etimer to set a timer event for your own process after
a certain period (for example to flash a LED).
•
Make two processes, and use process events between them.
•
Make a Contiki application to read the NanoSensor
accelerometer and light sensors using the ADC on the
CC2430. Convert the values using the sensor data sheets
and print them out periodically.
•
Make Contiki sensor libraries for the NanoSensor buttons and
sensors (using code from above) and use them to print
events.
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Contiki uIP
•
Make an application which uses uIP protosockets, and
spawns protothreads to handle both UDP and TCP sockets.
•
Make a client application and a server application which
communicate between each other over UDP.
•
Design a publish/subscribe protocol implementation over
UDP/6LoWPAN using the MQTT-S specification (simplified).
Implement Publisher, Subscriber and Broker applications.
•
Use MQTT-S to publish and subscribe to NanoSensor
buttons and sensor values.
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