Transcript Dia 1 - The Wireless Embedded Internet

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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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
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–
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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
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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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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 = Time that takes to go from sleep state to awake state
TTx  up = Transmitter setup time, i.e. time it takes for the transmitter to be ready
T
= Time in the Tx state
Tx
TRx  up = Receiver setup time, i.e. time it takes for the receiver to be ready
TRx = Time in the Rx state
Tidle = Time in the idle state
Tsleep = Time in the sleep state
N Tx








N Rx
TF
PTx
PRx
Pidle
Psleep
= 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
Pavg


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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
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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
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•
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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:
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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.
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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
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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:
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6LoWPAN interface(s)
6LoWPAN adaptation
Simple 6LoWPAN-ND
A full IPv6 protocol stack
• Other typical features include:
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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
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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
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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 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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