25,140 research outputs found
Extending the Real-Time Maude Semantics of Ptolemy to Hierarchical DE Models
This paper extends our Real-Time Maude formalization of the semantics of flat
Ptolemy II discrete-event (DE) models to hierarchical models, including modal
models. This is a challenging task that requires combining synchronous
fixed-point computations with hierarchical structure. The synthesis of a
Real-Time Maude verification model from a Ptolemy II DE model, and the formal
verification of the synthesized model in Real-Time Maude, have been integrated
into Ptolemy II, enabling a model-engineering process that combines the
convenience of Ptolemy II DE modeling and simulation with formal verification
in Real-Time Maude.Comment: In Proceedings RTRTS 2010, arXiv:1009.398
Adaptive control in rollforward recovery for extreme scale multigrid
With the increasing number of compute components, failures in future
exa-scale computer systems are expected to become more frequent. This motivates
the study of novel resilience techniques. Here, we extend a recently proposed
algorithm-based recovery method for multigrid iterations by introducing an
adaptive control. After a fault, the healthy part of the system continues the
iterative solution process, while the solution in the faulty domain is
re-constructed by an asynchronous on-line recovery. The computations in both
the faulty and healthy subdomains must be coordinated in a sensitive way, in
particular, both under and over-solving must be avoided. Both of these waste
computational resources and will therefore increase the overall
time-to-solution. To control the local recovery and guarantee an optimal
re-coupling, we introduce a stopping criterion based on a mathematical error
estimator. It involves hierarchical weighted sums of residuals within the
context of uniformly refined meshes and is well-suited in the context of
parallel high-performance computing. The re-coupling process is steered by
local contributions of the error estimator. We propose and compare two criteria
which differ in their weights. Failure scenarios when solving up to
unknowns on more than 245\,766 parallel processes will be
reported on a state-of-the-art peta-scale supercomputer demonstrating the
robustness of the method
On the Impact of Wireless Jamming on the Distributed Secondary Microgrid Control
The secondary control in direct current microgrids (MGs) is used to restore
the voltage deviations caused by the primary droop control, where the latter is
implemented locally in each distributed generator and reacts to load
variations. Numerous recent works propose to implement the secondary control in
a distributed fashion, relying on a communication system to achieve consensus
among MG units. This paper shows that, if the system is not designed to cope
with adversary communication impairments, then a malicious attacker can apply a
simple jamming of a few units of the MG and thus compromise the secondary MG
control. Compared to other denial-of-service attacks that are oriented against
the tertiary control, such as economic dispatch, the attack on the secondary
control presented here can be more severe, as it disrupts the basic
functionality of the MG
VLSI Architecture and Design
Integrated circuit technology is rapidly approaching a state where feature sizes of one micron or less are tractable. Chip sizes are increasing slowly. These two developments result in considerably increased complexity in chip design. The physical characteristics of integrated circuit technology are also changing. The cost of communication will be dominating making new architectures and algorithms both feasible and desirable. A large
number of processors on a single chip will be possible. The cost of communication will make
designs enforcing locality superior to other types of designs.
Scaling down feature sizes results in increase of the delay that wires introduce. The delay even of metal wires will become significant. Time tends to be a local property which will make the design of globally synchronous systems more difficult. Self-timed systems will eventually become a necessity.
With the chip complexity measured in terms of logic devices increasing by more than an order of magnitude over the next few years the importance of efficient design methodologies and tools become crucial. Hierarchical and structured design are ways of dealing with the complexity of chip design. Structered design focuses on the information
flow and enforces a high degree of regularity. Both hierarchical and structured design encourage the use of cell libraries. The geometry of the cells in such libraries should be parameterized so that for instance cells can adjust there size to neighboring cells and make the proper interconnection. Cells with this quality can be used as a basis for "Silicon Compilers"
- …