Idling along, (or what to do in the idle task)

If you are using an RTOS in your latest design then no doubt you have an idle task. (Most of the time, the idle task is explicit and is the user task with the lowest priority; sometimes it’s built into the RTOS). It’s been my experience that the idle task is an interesting beast. On […]

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Efficient C Tip #13 – use the modulus (%) operator with caution

This is the thirteenth in a series of tips on writing efficient C for embedded systems.  As the title suggests, if you are interested in writing efficient C, you need to be cautious about using the modulus operator.  Why is this? Well a little thought shows that C = A % B is equivalent to C = […]

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Median Filter Performance Results

In my earlier post on median filtering I made the claim that for filter sizes of 3, 5 or 7 that using a simple insertion sort is ‘better’ than using Phil Ekstrom’s technique.  It occurred to me that this claim was based upon my testing with 8 bit processors quite a few years ago, and that the […]

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Median filtering

NOTE: I have heavily edited this blog post since it was originally published, based on some recent testing If your engineering education was anything like mine then I’m sure that you learned all about different types of linear filters whose essential objective was  to pass signals within a certain frequency band and to reject as far […]

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Sorting (in) embedded systems

Although countless PhD’s have been awarded on sorting algorithms, it’s not a topic that seems to come up much in embedded systems (or at least the kind of embedded systems that I work on). Thus it was with some surprise recently that I found myself needing to sort an array of integers. The array wasn’t […]

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Horner’s rule addendum

A few weeks ago I wrote about using Horner’s rule to evaluate polynomials. Well today I’m following up on this posting because I made a classic mistake when I implemented it. On the premise that one learns more from one’s mistakes than one’s successes, I thought I’d share it with you. First, some background. I had some […]

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Horner’s rule and related thoughts

Recently I was examining some statistical data on the performance of a sensor against temperature. The data were from a number of sensors and I was interested in determining a mathematical model that most closely described the sensors’ performance. Using the regression tools built into Excel, I was looking at the various models, from a […]

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Modulo Means (reprised)

In my previous post I had asked for some input on how to compute the mean of a phase comparator. Bruno Santiago suggested converting the phase readings to their Cartesian co-ordinates and averaging the resulting (X, Y) data, and then converting the means of X & Y back into a phase angle. Well kudos to […]

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Modulo means

Normally on this blog I’m either giving my opinions on embedded matters, or offering tips on how to do things better. Well today I’m turning the tables, as I’d like your help. Yesterday I ran into a rather perplexing problem, which I’d be interested to see if any of my readers can solve. In a […]

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Integer Log functions

A few months ago I wrote about a very nifty square root function in Jack Crenshaw’s book “Math Toolkit for Real-time Programming”. As elegant as the square root function is, it pails in comparison to what Crenshaw calls his ‘bitlog’ function. This is some code that computes the log (to base 2 of course) of an integer […]

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