1. TinyOS Programming Boot Camp Part III: Hardware Tour
David Culler, Jason Hill, Rob Szewczyk, Alec Woo
U.C. Berkeley
2/9/2001

2. Hardware Tour

3. Outline Design overview Connector bus Sensor motherboard Sensor boards
Supporting hardware
Resources

4. Design Rationale Want to experiment with a wide variety of sensors
Need a wide variety of interfaces, analog and digital
Sensor platforms should be easy to design
Want to preserve processor and communication module
Major investment in SW and programming environment
Want interoperability between the various types of sensors
Every sensor node needs communication to be useful
Need a fixed interface to match the sensor modules with processor and communication

5. Design Rationale Main board requirements Sensor requirements
Easy to program and debug
Need an easy access to most signals in the system
Need standard interfaces
Basic self-monitoring and maintenance capability
Ability to reprogram remotely
Ability to control radio cell size
Ability to monitor signal strength
Other self monitoring added on sensor packs
Sensor requirements
Digital serial interfaces
Analog sensor support
Ability to control on/off state of individual sensors

6. Mote Connector Schematics

7. Mote Expansion Connector
Documented hardware interface
Swap components on either side of the connector while preserving investment in sensors or main boards
Sensor interfaces
4 lines dedicated to switching components on and off
7 analog voltage sensing lines
2 I2C busses
SPI
UART lines
Debugging aids
All radio-related signals: RX, TX, base band, control signals, signal strength
Programming interfaces
SPI and reset signals for the main processor and the coprocessor
Ground, Vcc for both analog and digital circuits
12 lines reserved for future use

8. Power Lines Need to control on/off state of individual sensors
Independently switched, used as outputs
Capability
Sink up to 20 mA, source a bit less
If more current is required by a sensor circuit, use MOSFETs
No higher level protocol attached
The place to implement functionality not provided by standard interfaces

9. Analog Lines and AD Conversion
Most sensors provide an analog interface
Simple voltage dividers with photo resistors, thermistors, etc.
Whetstone bridges, condenser microphones, etc.
Need analog voltage sensing lines
10 bit ADC,  2 LSB=> 8 usable bits
 3 mV error
Rail-to-rail range
Sampling rate
Max 15.4 ksps in continuous sampling mode
Max 4 ksps in a single sampling mode
8 multiplexed channels
One dedicated to sampling BBOUT
Sampling rate high enough for most environmental phenomena
Interrupt driven, or polling version

10. I2C Bus 2-wire serial bus: clock and data
Clock is an “or” of all clock generators, the slowest clock generator dictates the speed
Bi-directional data line
Higher level protocol than UART or SPI
Defines a protocol for multiple device access, up to 128 devices per bus
Defines a multiple master arbitration
Allows for multi-byte transactions
Speed: up to 400 kbps
Software implementation
Soft timing constraints mean that the use of timers is not mandatory, use tasks instead
Either 1 bit or 1 byte per task
Many slave devices available
EEPROM used for logging and other permanent storage
IO extenders, ADC converters, sensors, etc.

11. SPI 3-wire, full duplex serial bus: clock, MISO, MOSI
Connector bus defines 2 SPI busses
Speed: up to 1 mbps
Hardware support on the main processor, software implementation on the coprocessor
Low-voltage programming interface to ATMEL microcontrollers
Interaction with coprocessor
Cyclic 16 bit distributed register

12. UART A standard way for exchanging information with a PC
Voltage conversion and connector required, provided by the programming board
Available speed: 2400 bps to 115 kbps
Most reliable for communication with PC: 19.2 kbps
Large clock rate errors at high sending rates
1 byte FIFOs
Hardware doesn’t buffer multiple bytes of either input or output
Operate in either polling or interrupt driven mode
TinyOS uses UARTs in interrupt driven mode

13. Rene: the Motherboard Main components Processor: ATMEL AVR 90LS8535
Reprogramming coprocessor
Short range radio
LEDs
I2C EEPROM

14. Rene Schematics

15. AVR Processor Core Clock speed: 4 MHz Memory IO capabilities
8 Kbytes of program memory (flash)
512 bytes of data RAM
512 bytes of EEPROM on chip (write: 4 ms/byte)
32 8 bit registers
IO capabilities
32 general purpose IO lines
Some lines also serve more specialized purposes, e.g. UART
10-bit 8-channel ADC
Connector interface means that the IO lines serve a more specific purposes
Interrupts
No external interrupts available
No interrupt queuing

16. Wakeup latency (cycles) Wakeup granularity (cycles)
AVR Processor Core
Timers
8 bit timer/counter – unused in current applications
16 bit counter – one comparator used for radio sampling, other functions unused
8 bit, externally clocked timer/counter – used for periodic sampling of sensors and sleep control
More advanced timer features (input capture, PWM output) are available, through not explicitly allocated on the connector, use at your own risk
Power consumption
Restrictions
No truly general purpose registers
Limited arithmetic/logic instructions
Current
Wakeup latency (cycles)
Wakeup granularity (cycles)
Active
6 mA -
Idle
2 mA 4 1
Power save
5 uA
122

17. Programming the Processor
Program the runtime memory image into a flash
No loader, no dynamic linker
Programming steps
Extract the code and data segments from an executable into an SREC file
Erase the current contents of the flash
Reset the processor
Download the program
Serial download protocol
Each download command contains the address, and the contents of to be stored
10 ms delay per byte of code
Verify the program: read the flash, match it against the source image
After reset, start executing C runtime
No ability to write the flash on the fly
Requires a coprocessor for reprogramming

18. Coprocessor Circuit Coprocessor: ATMEL AVR AT90S2343
2 Kbytes of code space
1 MHz internal clock
Required connections
SPI for programming the main microcontroller
RESET for the main controller
I2C for accessing EEPROM storage
Insufficient pins – I2C and SPI clock lines are shared
Minimal capability
Software SPI
Software I2C

19. Radio Circuit RFM Monolithics TR1000 916 MHz radio Processor interface
On/off keying at 10 kbps (max kbps)
Capable of 115 kbps using amplitude shift keying
Capable of turning on in 30 us
Low-power listening by switching on and off on a sub-bit granularity
Processor interface
RFM CNTRL 0 and 1 – switch between transmit, receive, and sleep
Raw, unbuffered access to transmit (RFM TX) and receive (RFM RX)
Requires DC balanced signal – an equal number of 1’s and 0’s in the signal
Sampling on reception and modulating on transmission done is software
Too much noise in received signal to use UART for sampling
too little flexibility offered by UART
Imposes real time constraints on the system
Power usage
Transmit current: 7 mA
Receive current: 4.5 mA
Sleep: 5 uA

20. Radio Signal Strength
Measuring the quality of reception from a node is useful
Aid in multihop routing decisions
Help with location estimation
Signal strength measurement
Based on base band sampling
Demodulated and amplified analog signal, fed into ADC channel 0
Raw samples further processed in TinyOS
Empirical evaluation*
*Klemmer, Waterson, Whitehouse, 2000

21. Radio Transmission Strength Control
Useful in networking experiments
Control the cell size
Allow for power savings
Principles of operation
Radiated power is proportional to the square of the current on RFM TX pin
Signal strength control
Controlled through a digital potentiometer (DS 1804), 0-50 kOhms
Currently no observable effects on power usage
Evaluation
Optimal transmission at the pot setting of 10 kOhms
Changing the range from 45 to 90 feet in an indoor environment
Changing the transmit strength has no effect on power usage
Effects secondary to shape/length of the antenna

22. LEDs Basic mote UI and a great debugging tool Power consumption: 6mA
LED consumes as much power as the main microcontroller
If power is a concern, turn them off!
LED 1 and LED 2 multiplexed with the signal strength potentiometer control
Use them for controlling any other DS 1804 pots, one at a time

23. Matching SW and HW: hardware.h
Define a hardware.h for each motherboard
Map motherboard abstractions onto physical pins
RFM RX, TX, and control pins
Allocate the connector pins onto the motherboard resources: PW lines, I2C busses, UARTs, etc.
Define a header file for each sensor board
Assign symbolic names (e.G. PHOTO_PWR) to the connector signals
Attempt to maintain a consistent convention in hardware design
Photo and temperature on the same signals in both basic and advanced boards

24. Mote Connector Caveats
Multipurpose lines
LED1 and LED2 are used to control the signal strength potentiometer. They can also be used to control digital pots on sensor boards
PW3 can be used as a PWM output
PW4 can be used as a timer input capture, useful for PWM inputs
Other restrictions
Relationship between the main processor and the coprocessor dictates that their SPI busses are permanently connected
Shortage of pins on the coprocessor dictates that the SPI SCK is shared with the I2C BUS 2 CLK
Cannot use this bus when the board is plugged into the programming port
Cannot use the logging component when a board is set up for programming

25. Basic Sensor Board Sensors Photo resistor – PW1 and ADC1
Thermistor – PW2 and ADC2
Prototyping area

26. Vibes Sensor Board Vibes Photo resistor: PW1 and ADC1
Thermistor: PW4, ADC6
2 axis accelerometer: ADC2 and 3, PW2
Digital temperature: I2C Bus 1

27. 2xMAG Board Sensor 2 axis magnetometer optimized for vehicle detection
Resources: PW2, 3, and 4, ADC 6 and 7

28. Programming Board SPI interface through the parallel port
Programming either the main microcontroller or the coprocessor with a flip of the switch
RS232 connector
Voltage conversion
CTS/RTS signal grounded
Program the serial port accordingly

29. Building Your Own Tools Complete designs
OrCAD – capture and layout tools
Complete designs
Rene
Basic
Vibes
2xMAG
Base board

30. Resources Datasheets Schematics ATMEL 8535 datasheet
RFM TR1000 datasheet
24WC256 EEPROM
ADXL202 2 axis accelerometer
HMC axis magnetometer
Schematics
Rene motherboard
Basic sensor board
Vibration sensor board
Vehicle detection board
Base board
Debugging board

31. Exercise Basic sensor modification
Add a buzzer to the basic sensor board
Connect buzzer to Vcc and to an unused PW line. The buzzer should turn on when pulled PW is pulled low
Write a component to interface with a buzzer
Use a similar component as a template
Using the previous application as a template, create an application which beeps when the average light level drops below some threshold (audience choice)