WRITINGS

• Misc.
  • Substituting fonts in .eps and .fig files
    A couple quick hacks I cooked up to bulk-edit my .fig (and resulting .eps) figure source files to convert them from Times-Roman (for papers) to Helvetica (for slides). Also included a script to bulk-convert them to .jpg if necessary.
  • Chaucer's description of a Grad Student from 600 years ago
    From his Prologue to the Canterbury Tales, circa 1392.
  • Correlation of Ground-Level Computer Installation Error Rates with Solar Activity
    The data suggests that the amount of solar activity does indeed increase the probability of errors in computer systems. Boeing Radiation Effects Laboratory used to have many papers (archived copy) on this topic. There are more links in Berke Durak's "On the need to use error-correcting memory" and its follow-ups.
  • Canadian Space Gazette (November 2005)
    I wrote "Terrapin Station: An Alternative Approach To Space Exploration" to argue that developing self-sustaining stations should be done sooner than later, and would have great technology transfer potential on Earth. Since then, I've been told that the Van Allen belts pose a bit of a problem...
• Code Structure and Optimization
  • Some Thoughts On Machine Code Organization
    Just a digression on the relationship between iterative, recursive, and threaded machine code, and how the choice of fundamental parameter-passing structure leads to different programming environments.
  • Survey of Loop Transformation Techniques (Slides: PDF PPT)
    A report on all the loop transformation techniques I had to learn in Parallelizing Compilers. If your algorithm is memory-bound, the speedup can be remarkable: "How We Made Our Face Recognizer 25x Faster" In C, in some cases, you'll likely have to use the obscure 'restrict' keyword to give the compiler a chance, else the potential for pointer aliasing makes dependency analysis very hard. Not having array accesses being pointer-based is the main strength of Fortran for such things.
• Parallelism and Message-Passing
  • HashLife on GPU
    A mostly-failed attempt at implementing Gosper's HashLife algorithm on a GPU using CUDA. Hopefully this will help someone else get it right.
  • Message-Passing Concurrency on Shared-Memory Multiprocessors
    Inspired by Erlang, I tested various locking schemes for a message mailbox. Even with thousands of threads contending for a single lock, it turns out that a single, simple Pthread mutex works best due to playing very well with the Linux process scheduler.
• Chaotic Systems and Neural Engineering
  • Finding the Largest Lyapunov Exponent
    In short: use Rosenstein's algorithm over Wolf's. It's much faster and more accurate. (MATLAB code)
  • Second-Order Wiener-Bose Model of a FitzHugh-Nagumo Giant Squid Axon Model
    Finding the number of Laguerre functions is easy enough, but scaling them to the available number of data points is tricky. I initially tried to do it all in MATLAB, but broke down and used LYSIS instead for the modelling. The MATLAB code contains a fast memoized recursive Nth-order Wiener-Bose filter implementation, if you need such a thing.
• Asynchronous Circuits
  • Burst-Mode Locally-Clocked Asynchronous Circuits
    (My initial foray into asynchronous circuits.) I chose Nowick's Burst-Mode (hazard-free two-level logic) circuits to implement an active and a passive version of an asynchronous four-phase handshake circuit, then used them to build self-timed modules which can generate local clocks with a variable period, exchange data with other asynchronous systems (with early handshake termination if desired), or act as input/output ports with provisions against metastability. I also outline the use of these modules to create an asynchronous implementation of the Gullwing computer architecture.
  • Optimization of Burst-Mode Circuits Using Logical Effort Theory
    (Contains nice nutshell explanations, calculations, and experiments using Logical Effort Theory on control circuits.) The logical effort and parasitic delay of static CMOS logic gates are determined through simple simulation experiments based on Logical Effort theory. This calibrated model is then used to calculate near-optimum gate sizes and path delays for an active/passive pair of Burst-Mode circuits under load. Finally, an extension of Logical Effort theory is applied to the circuits in order to determine their critical delay under an equal gate delay model and compare them to other asynchronous control circuits.