Advantages and Pitfalls of Moving from an 8 bit System to 32 bit Architectures.

International audienceThis paper explores the considerations of designers of embedded systems when they come to choosing the bit width of the embedded CPU architecture, especially in the domain of System on Chip designs. Two typical architectures are compared and contrasted, one 8 bit and the other 32 bits, the 8051 and the Cortus APS3. Embedded systems are a designed with a number of constraints not found in other computer systems. In addition they are also expected to give real-time responses, often with limited resources. Received ideas are explored and evaluated in the light of benchmarks and concrete examples. Attention is paid to modern implementation and programming methodologies. Issues such as power consumption, code density, suitability for real time systems, ease of software development are discussed

High performance extendable instruction set computing

In this paper, a new architecture called the extendable instruction set computer (EISC) is introduced that addresses the issues of memory size and performance in embedded microprocessor systems. The architecture exhibits an efficient fixed length 16-bit instruction set with short length offset and immediate operands. The offset and immediate operands can be extended to 32 bits via the operation of an extension flag. The code density of the EISC instruction set and its memory transfer erformance is shown to be significantly higher than current architectures making it a suitable candidate for the next generation of embedded computer systems. The compact EISC instruction set introduces data dependencies that seemingly limit deep pipeline and superscalar implementations. This paper suggests a mechanism by which these dependencies might be removed in hardware

Capability Memory Protection for Embedded Systems

This dissertation explores the use of capability security hardware and software in real-time and latency-sensitive embedded systems, to address existing memory safety and task isolation problems as well as providing new means to design a secure and scalable real-time system. In addition, this dissertation looks into how practical and high-performance temporal memory safety can be achieved under a capability architecture. State-of-the-art memory protection schemes for embedded systems typically present limited and inflexible solutions to memory protection and isolation, and fail to scale as embedded devices become more capable and ubiquitous. I investigate whether a capability architecture is able to provide new angles to address memory safety issues in an embedded scenario. Previous CHERI capability research focuses on 64-bit architectures in UNIX operating systems, which does not translate to typical 32-bit embedded processors with low-latency and real-time requirements. I propose and implement the CHERI CC-64 encoding and the CHERI-64 coprocessor to construct a feasible capability-enabled 32-bit CPU. In addition, I implement a real-time kernel for embedded systems atop CHERI-64. On this hardware and software platform, I focus on exploring scalable task isolation and fine-grained memory protection enabled by capabilities in a single flat physical address space, which are otherwise difficult or impossible to achieve via state-of-the-art approaches. Later, I present the evaluation of the hardware implementation and the software run-time overhead and real-time performance. Even with capability support, CHERI-64 as well as other CHERI processors still expose major attack surfaces through temporal vulnerabilities like use-after-free. A naive approach that sweeps memory to invalidate stale capabilities is inefficient and incurs significant cycle overhead and DRAM traffic. To make sweeping revocation feasible, I introduce new architectural mechanisms and micro-architectural optimisations to substantially reduce the cost of memory sweeping and capability revocation. Another factor of the cost is the frequency of memory sweeping. I explore tradeoffs of memory allocator designs that use quarantine buffers and shadow space tags to prevent frequent unnecessary sweeping. The evaluation shows that the optimisations and new allocator designs reduce the cost of capability sweeping revocation by orders of magnitude, making it already practical for most applications to adopt temporal safety under CHERI.CSC Cambridge Scholarshi

Tree Parity Machine Rekeying Architectures

The necessity to secure the communication between hardware components in embedded systems becomes increasingly important with regard to the secrecy of data and particularly its commercial use. We suggest a low-cost (i.e. small logic-area) solution for flexible security levels and short key lifetimes. The basis is an approach for symmetric key exchange using the synchronisation of Tree Parity Machines. Fast successive key generation enables a key exchange within a few milliseconds, given realistic communication channels with a limited bandwidth. For demonstration we evaluate characteristics of a standard-cell ASIC design realisation as IP-core in 0.18-micrometer CMOS-technology

Normalizing or not normalizing? An open question for floating-point arithmetic in embedded systems

Emerging embedded applications lack of a specific standard when they require floating-point arithmetic. In this situation they use the IEEE-754 standard or ad hoc variations of it. However, this standard was not designed for this purpose. This paper aims to open a debate to define a new extension of the standard to cover embedded applications. In this work, we only focus on the impact of not performing normalization. We show how eliminating the condition of normalized numbers, implementation costs can be dramatically reduced, at the expense of a moderate loss of accuracy. Several architectures to implement addition and multiplication for non-normalized numbers are proposed and analyzed. We show that a combined architecture (adder-multiplier) can halve the area and power consumption of its counterpart IEEE-754 architecture. This saving comes at the cost of reducing an average of about 10 dBs the Signal-to-Noise Ratio for the tested algorithms. We think these results should encourage researchers to perform further investigation in this issue.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The Chameleon Architecture for Streaming DSP Applications

We focus on architectures for streaming DSP applications such as wireless baseband processing and image processing. We aim at a single generic architecture that is capable of dealing with different DSP applications. This architecture has to be energy efficient and fault tolerant. We introduce a heterogeneous tiled architecture and present the details of a domain-specific reconfigurable tile processor called Montium. This reconfigurable processor has a small footprint (1.8 mm$^2$ in a 130 nm process), is power efficient and exploits the locality of reference principle. Reconfiguring the device is very fast, for example, loading the coefficients for a 200 tap FIR filter is done within 80 clock cycles. The tiles on the tiled architecture are connected to a Network-on-Chip (NoC) via a network interface (NI). Two NoCs have been developed: a packet-switched and a circuit-switched version. Both provide two types of services: guaranteed throughput (GT) and best effort (BE). For both NoCs estimates of power consumption are presented. The NI synchronizes data transfers, configures and starts/stops the tile processor. For dynamically mapping applications onto the tiled architecture, we introduce a run-time mapping tool

Low Power Processor Architectures and Contemporary Techniques for Power Optimization – A Review

The technological evolution has increased the number of transistors for a given die area significantly and increased the switching speed from few MHz to GHz range. Such inversely proportional decline in size and boost in performance consequently demands shrinking of supply voltage and effective power dissipation in chips with millions of transistors. This has triggered substantial amount of research in power reduction techniques into almost every aspect of the chip and particularly the processor cores contained in the chip. This paper presents an overview of techniques for achieving the power efficiency mainly at the processor core level but also visits related domains such as buses and memories. There are various processor parameters and features such as supply voltage, clock frequency, cache and pipelining which can be optimized to reduce the power consumption of the processor. This paper discusses various ways in which these parameters can be optimized. Also, emerging power efficient processor architectures are overviewed and research activities are discussed which should help reader identify how these factors in a processor contribute to power consumption. Some of these concepts have been already established whereas others are still active research areas. © 2009 ACADEMY PUBLISHER