Shubhendu S. Advances in semiconductor technology have let microprocessors integrate more than a million transistors on a single chip. The Alpha microprocessor1,2 uses million transistors to integrate an Alpha processor core, a 1. In the 0. A fully configured, processor, shared-memory system can support up to 4 terabytes of Rambus memory and hundreds of terabytes of disk storage.
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Current wireless systems only Exploiting local communication and appli- scratch the surface of possibilities emerging cation-specific protocols can drastically reduce from the integration of low-power commu- size, cost, and power use in wireless devices. Generally, when people consider with the nearest high-power control tower, wireless devices they think of such items as but only with their local peers.
Peer-to-peer cell phones or personal digital assistants, items networking techniques provide a flexible with high costs and energy requirements that meshlike interconnect that shuttles data target specific, highly standardized applica- between thousands of tiny embedded devices.
A A handful of the devices might act as bridges new direction in wireless system design, how- between a local embedded communication Jason L. Hill ever, is extending wireless connectivity to mesh and a traditional data network. Figure 1 small, low-cost embedded devices for a wide depicts a precision agriculture deployment— David E. Culler range of applications. Application possibilities for miniature wire- Researchers are developing new algorithms for University of California, less sensing devices include inventory asset data aggregation, ad hoc routing, and distrib- tracking, roadside traffic pattern and open uted signal processing for low-power peer-to- Berkeley parking spot detection, individual plant mon- peer wireless networks.
As researchers envision itoring for precision agriculture, habitat mon- smaller and lower-cost devices, the range of itoring in nature preserves, and advanced application scenarios grows dramatically. The mili- The Mica wireless platform serves as a foun- tary could blanket fields with sensors to detect dation for the emerging possibilities. Pictured troop movement.
Sensors might enable civil in Figure 2, the Mica platform measures 1. Integrating hundreds of thousands of suited for self-configuring multihop wireless sensing and control points could provide new networks. With sensing, communication, and insights into the state of the world.
Ad hoc, wireless embedded network for precision agriculture. Sensors detect tem- perature, light levels, and soil moisture at hundreds of points across a field.
The system communicates the data over a multihop network for analysis. Nearly a hundred research groups cur- rently use Mica nodes to explore networking techniques, data analysis, distributed algo- rithms, networked services, programming, and novel applications.
We created Mica with off-the-shelf hardware, but the architecture and its capabilities represent what could be implemented in just a few square millimeters of custom silicon. Instead of defining narrow, standardized application interfaces, Mica provides a set of richly interconnected primitives such as data serializers and timing extractors to facilitate cross-layer optimiza- tions.
To explore novel systems approaches, researchers can develop customized protocols Figure 2. Mica node. First, power consumption must be drastically Conventional wireless design comparison reduced.
A deeply embedded, battery-operat- An explanation of the current wireless archi- ed device might need to operate for years on a tectures and their shortcomings for deeply pair of AA batteries or a lithium coin cell.
Deeply embed- microamps range, requiring powering down ded wireless networks differ in several key most of the device much of the time—a cell respects from traditional wireless scenarios. In a deeply embedded wire- less network, however, devices typically require less than a milliwatt to communicate with their neighbor nodes. This drastic reduction in transmission power must be complemented Voice codec Application controller by a highly efficient protocol processing mech- anism.
A pair of AA batteries would last less than eight hours with RF protocol processing a standard Thus, in deeply embedded wireless networks, protocol pro- cessing must be optimized for ultralow-power Power regulator operation, not for high data rates.
Traditional and deeply embedded wireless RF transceiver devices also differ in their required level of flex- ibility. Peer-to-peer protocols and in-network processing implementations must adapt to Figure 3. Typical cell phone architecture. The design is parti- meet application needs in sensor networks. This hundredfold power with a single and highly specific algorithm, and consumption reduction mandates drastic complex radio controllers provide the low-level changes to system architecture.
Second, many channel processing. Figure 3 depicts a gener- deeply embedded systems cannot rely on a pre- alized cell phone architecture. A prolonged deployed, powerful infrastructure for support. In a peer-to- components. New services are typically over- peer multihop network, typically, only the last laid on the established structure. An audio stream provides an IP data communi- advantage of a peer-to-peer architecture is that cation stack.
The An average cell phone uses to specific media access control MAC 1,mW to reach a distant cell tower. In such protocol. For example, cation-specific requirements.
Additionally, the if sensor data is sampled only once per minute, complex controllers surrounding the radio it might be acceptable to delay transferring the consume significant power bringing the radio data to the consumer for several seconds, allow- online, making low-power operation difficult. Originally envisioned to replace the weeks to years. Rather than a narrow, eight. While the specification lets devices par- standardized interface to a complex radio con- ticipate in logical communication groups dis- troller, our deeply embedded designs use sim- tinct from the primary master-slave ple radios with much of the RF channel relationship, it has a powerful master in direct control exposed to software through a rich control of a small collection of physically close interface.
Rather than dedicated protocol con- low-power devices. In the deeply embedded trollers, we provide simple accelerators for networks we envision—a mesh of thousands protocol primitives that are composed in soft- of interconnected embedded nodes—the key ware.
Rather than partitioning the design into to power, cost, and size reduction is neighbors dedicated subsystems, this new approach forwarding and routing data. Ad hoc, multi- pools processing resources and uses fine- hop interconnections could be simulated as grained multithreading to dynamically allo- an overlay on the Bluetooth master-slave phys- cate subtask processing.
While each of these ical layer, but are likely to be inefficient. Addi- differences affects performance on simple tionally, the Bluetooth device power tasks, their real impact is made by enabling consumption is still an order of magnitude high-level software optimizations. Cell phones, tion, power management, and sensing into a wireless local area networks, and Bluetooth pro- small experimental platform. The current form tocols must meet strict bandwidth and latency factor 1.
Cell phone voice traffic trans- pair of AA batteries, although we have com- missions cannot suffer signal delays that cause pressed a variant of the design to about the size noticeable audio variations. Additionally, a of a 2.
These demands several years on a single set of batteries. Mica require that these devices meet strict protocol improves experimental flexibility by including design specifications.
In deeply embedded wire- an expansion bus that connects to a wide array less networks, however, we can exploit trade- of sensor boards. Additionally, to provide each node with a unique TR radio transceiver identification, we include a Maxim DS silicon seri- Figure 4. Mica architecture block diagram. The direct connection between application con- al number—a low-cost ROM troller and transceiver enables flexibility in meeting application demands.
Hardware acceler- device with a minimal elec- ations optionally assist in communication protocols. The Mica radio module mal temperature, barometric pressure, mag- consists of an RF Monolithics TR trans- netic fields, light, passive infrared frequency, ceiver and a set of discrete components to acceleration, vibration, and acoustics.
A quick cy of At maximum transmission survey of the major modules provides a gen- power, it outputs approximately 0. This 8-bit actual communication is occurring. It stores sensor data logs and tem- Normally, programming of these embed- porarily holds program images received over ded microcontrollers occurs during manufac- the network interface. Breakdown of active and idle power consumption for Mica Kbyte program memory. This prevented hardware. Mica operates with inexpensive alka- LEDs 10 0 line batteries that produce between 3.
We chose the Maxim chip because of its small any RSprotocol-based device. Dozens of form factor and high efficiency. The convert- sensor boards with a variety of sensors have er takes input voltage as low as 1. This supplies a clean, stable nector. It has even been used to let the Mica voltage source for the rest of the system.
Input node control a handful of inch-sized micro- voltage significantly affects the TR trans- robotic platforms. This com- microcontroller. The radio will not operate, ponent-based structure lets an application however, without the boost converter enabled. This lets high- to interface with a variety of sensing and pro- level application code and low-level protocol gramming boards.
We divided the connector code coexist on a single CPU. However, low-level system events gramming the microcontrollers. TinyOS shields the the device and communicate with other application-level processing from the under- devices, such as a PC serving as a gateway lying concurrent scheduling, yet exposes low- node.
Additionally, it contains a standard level system components to meet their UART interface to control or provide data to real-time requirements. In contrast, Bluetooth processing. This partitioned approach requires radio chipsets dictate bit rates, signaling enough power in the application and system- schemes, data-encoding methods, framing, level processors to handle the peak demand; MAC protocols, and the routing scheme to though system demand for these two proces- the host processor.
With Bluetooth, the oper- sors might never occur simultaneously. The ating system can only spool packets across the pooled processing approach used in TinyOS interface; delays through the interface have a allows dynamically allocating a single CPU to large, unpredictable variance, and the system a given task, so peak demand is close to aver- or application components cannot observe the age processing.
For example, the radio pack- activity or physical characteristics of the radio et start symbol detection requires a peak of channel. A partitioned system the controller direct access to the signal would require a total of 5 MIPS; however, strength of the incoming RF transmission. It using a shared pool approach, slightly more also allows sampling the level of background than 3 MIPS could handle this application.
Using this information in multihop decreases further because of overprovisioning networking applications can dramatically of the partitioned system to the worst case. Interactions between Furthermore, if a more efficient mechanism transmitter and receiver are very predictable, for performing start symbol detection were as is the delay through the radio interface.
This direct, faces between system components are not low-level interface to the radio provides flex- constrained by narrow chip-to-chip communi- ibility for application developers.
Researchers cation mechanisms defined by physical hard- from the University of California, Los Ange- ware. System components can provide rich les, have exploited this flexibility to create interfaces to other components to enable cross- energy-aware MAC protocols. Additionally, software-based interfaces facilitate interface evolution as new Communication accelerators features are added to system components.
History[ edit ] The Alpha was revealed in October by Compaq at the 11th Annual Microprocessor Forum, where it was described as an Alpha with a 1. Changes to the Alpha core included a larger victim buffer, which was quadrupled in capacity to 32 entries, 16 for the Dcache and 16 for the Scache. It was reported by the Microprocessor Report that Compaq considered implementing minor changes to branch predictor to improve branch prediction accuracy and doubling the miss buffer in capacity to 16 entries instead of 8 in the Alpha However, the original schedule was delayed, with the tape-out in April instead of late It operated at 1.
Damuro The design originally was intended to support multiple control chips to allow implementation of additional instructions such as the Commercial Instruction Set CISbut This avoided unproductive Scache accesses, reducing power consumption. Alpha topic The Netwprk is an unfinished microprocessor that implements the Alpha instruction set architecture ISA developed by Digital Equipment Corporation and later by Compaq after it acquired Digital. Alpha This paper has citations. Member feedback about DEC Alpha: Targets were devices such as newer personal digital assistants and set-top boxes.