Written by Chris Woodall on 23 Dec 2016
I started making some
.gifs to embed in documentation and my notes as I
develop Rusty Nail. I always have to lookup how to
convert the images to
gifs. Every time I am also concerned with how big the
.gifs are so after doing some looking around I made a little script which
giflossy) to take an input
webm, or any video that ffmpeg can decode.
The process is this:
ffmpegsplits the video into a directory of
convertthose images and stitches them together into one
gifand allow a stage to resize it and also change the color. The
giflossyplug-in also can apply lossy compression to the gif video during the optimization step.
Read on for the script.
Written by Chris Woodall on 19 Dec 2016
I decided to customize my bash prompt. I initially started off with the following requirements:
After some work I came up with the prompt shown above. I am excited to keep using it and customizing it, I am also happy that I decided to use unicode in the prompt. I have been avoiding unicode in general, but Rust has convinced me that I should try to accept unicode into my life more readily!
After going through the process, here are sometake aways:
printfsupports unicode more reliably than echo. I had some trouble getting echo to do what I want to do
I hope you enjoy! Below is the code for my prompt! Put it into you
.bashrc file depending on your preference. If
you want to use it.
Written by Chris Woodall on 18 Dec 2016
I completed my first Coursera course, which was “Machine Learning” with Andrew Ng from Stanford University. The course was well taught and concentrates on building a solid base for applying Machine Learning to a variety of problems. Andrew Ng uses examples motivated by real-world problems to show how you might apply the algorithms taught. I highly recommend the course if you are looking to take a MOOC and have an interest in machine learning. I learnt a lot, but still need to apply the knowledge in some personal projects of mine.
Read on for more thoughts on the course and tips on how to succeed.
Written by Chris Woodall on 19 Nov 2016
For week 7 of the Coursera Machine Learning course we
learned about Support Vector Machines (SVM). SVMs are a useful and
powerful tools for solving classification problems. They can be tailored to
solve complicated classification boundaries, and don’t suffer from some of the
down sides of optimizing neural networks. One of the
example problems uses an SVM to classify spam emails. A SVM implementation
written in MATLAB/Octave is used, but for further work libsvm (or
another SVM library) is recommended. To get
libsvm working with Octave in
Ubuntu 14.04 there are a few steps that are not obvious. I did not find very
many instructions so I compiled the steps I followed to get a stable Octave
libsvm. Read on for details.
Written by Chris Woodall on 06 Nov 2016
A few weeks ago I was setting up multiple embedded systems using the NXP Kinetis K64F12 family of microcontrollers. Do to an oversight a few of the different systems had different input clock frequencies, but all were intended to work at the same output clock frequency. This is not a major issue and the ARM Cortex-M4 processors are designed to solve this issue using a phase-locked loop (PLL). A PLL can take a clock, of one frequency and output a rather clean clock of another frequency; however, it must be properly configured. My problem now was a configuration, and mathematics problem. The parameters are calculated using the following equation:
, where and are the parameters needed for the configuration. and and are your input and output frequency which you know ahead of time.
A solution to this equation is straightforward but requires a little bit of guessing, and also checking your answers against a series of constraints specified in the datasheet. The details of this equation and its related constraints will be approached later. I wanted to automate this task so in the future I could just adjust these values without having to dig out the datasheet and do the math again. Also to possibly automate making the clock configuration code to prevent me from being the only person who understood how to configure the clocks.
What is someone who loves automation to do? Well, you could solve the equation directly. However, Michael Abed introduced me to a program and library called Z3 which is a constraints solver from Microsoft Research which I found interesting and wanted to do a simple project with since I thought it might be useful in the future. Also, this problem is well-suited as it can take a series of equations and constraints and search the solution space rather trivially easily. Also, it has a way of deciding if no solution is possible. So I decided to use the Z3 python bindings to create a python library, with a command line tool and a web API for solving this problem. This is most certainly overkill, but considering how easily it all went together I would do it again to solve similar problems.
Written by Chris Woodall on 10 Oct 2016
I have been learning Rust lately, which has been an awesome and
rewarding experience thus far. However, at work, and on many of my embedded side
projects I use C/C++ quite extensively. But error handling ends up being
a major pain point and can make an otherwise rather simple API into a disaster.
This can be especially true if you are committed to avoiding throwing exceptions for various
performance and real-time reliability reasons. This is where Rust’s model comes
in as a possibly solution (or at the very least an interesting one): the use of
Result<T, E> types and the
Option<T> type. For the time being I am going to concentrate on the
Option<T> type and write about the
Result<T, E> type in a future post.
The code for this blog post can be found on github as cpp-option!
Written by Chris Woodall on 07 Jul 2013
A nice and simple hack for attaching things onto bikes without dropping a ton of money. Before you buy your P-Clamps, or Rubber Coated Metal Clamps, make sure to measure the diameter of the tube on your bike you want to attach the clamp to. You can get them from Grainger and McMaster-Carr, but they are also easily found in your local hardware store.