Follow me down the optimization rabbit hole

Intro I grew up in the era of 8-bit computers (late 1970s). At that time, basically anything done on a computer meant it was written in English and text was written using 7-bit ASCII characters stored in 8-bit bytes. It wasn't until a few years later that IBM and Microsoft added support for accented characters to be more inclusive of European languages. The initial solution was to shoehorn a bunch of characters and symbols into the "unused space" of values 128 to 255. This became known as Extended ASCII. There were multiple de-facto standards, but Microsoft's seemed to win; they called it codepage 1252 . This stuck for a while until the various countries got together to create "one character set to rule them all" and called it Unicode. In this new world, the old ASCII 7-bit set was slotted into the first 128 spots followed by the accented characters, symbols and then Asian and middle-eastern characters came after that. There are literally thousands of symbol...

Intro The ESP32 (there are now quite a few varieties), is an incredibly versatile microcontroller. It's main value proposition has always been that it's a low cost MCU with WiFi capability - something that was relatively unique when it was first released. The processing speed and internal RAM size prevent it from doing tasks that Linux machines like the Raspberry Pi series can do, but there is some overlap where the ESP32 can still surprise you with its abilities. I've been working on projects which use a variety of ESP32s as video and animation playback devices. I recently released an optimized MPEG-1 player ( https://github.com/bitbank2/pl_mpeg ) and was looking at other applications for video playback. Until now, I've seen multiple projects which have been using my JPEGDEC jpeg decoder library to play motion-jpeg videos. I was curious to see if anyone had published a project to play motion-jpeg streams from public IP camera URLs. I didn't find any, so I thought ...

I've been wanting to create a series of lessons on code optimization and something I encountered yesterday seemed like a good starting point. There are many ways to get the same results in software; not all are efficient. Optimizing code is one of those skills that any programmer can do, it just takes a little extra experience and patience. In this lesson I'll walk you through the thought process of how I analyze code followed by the steps to improve it. I will attempt to show you how code looks "through my eyes". We're going to look at part of the font rendering code within LVGL. By optimizing this code, I'm not intending this lesson to be a criticism of that project, it's just a good example of code I analyze. Here's the code in question: ( LVGL Github link ) The purpose of this type of optimization is to improve the C code for all target systems, not to slice 1 clock cycle off of register reads. A 'normal' C programmer will look at this code...

Intro This is an idea I've had for quite a while and have created limited-scope versions for a few customers. The idea is that developing software (any software) is challenging and often frustrating. Developing software for embedded devices is often much more challenging and frustrating. The extra time spent waiting for edit/compile/run cycles and more limited tooling hurts productivity. The simulators I've created allow you to work on Arduino projects as native MacOS/iOS projects. (Photo of an old iPhone running my simulation of a Guition ESP32-2432S028R) What's the benefit? Using the Apple tools, specifically Xcode and Instruments, I'm able to run/debug/profile my code much quicker and with a much friendlier set of tools. For my own work, the productivity boost has been tremendous. My Arduino imaging and video codecs ( JPEGDEC , JPEGENC, PNGDEC, PNGENG, AnimatedGIF, pl_mpeg, TIFF_G4, G4_ENC) were all written, debugged and profiled on the Mac as a native MacOS app. It...

Intro DMA ( direct memory access ) is a topic that's similar to pointers in C - it's not easy for everyone to visualize how it works. My goal for this blog post is to explain, in the simplest way possible, how it works and why your project can benefit from proper use of it. What's it all about? DMA is a useful feature for a CPU/MCU to have because it means that data can move around without the CPU (your code) having to do the work. In other words, DMA can move a block of data from memory-to-memory, peripheral-to-memory or memory-to-peripheral independently from the CPU. For people used to programming multi-core CPUs with a multi-threaded operating system, that may not sound very special. For those of us familiar with programming slow, low power, single threaded, embedded processors, it can make quite a difference. Here's a practical example - sending data to an SPI device (e.g. a small LCD display): Without DMA <prepare data1 - 10ms > <send data1 to SPI - 10ms...

Intro Most of my blog posts share info about a general topic or highlight something interesting that I've discovered. This post will be essentially a tutorial or "how-to". Users of my display libraries probably know that they support Windows BMP files as a source of graphics. My latest eink libraries (both SPI and parallel - bb_epaper, FastEPD) both support this format in addition to a special lossless compression format I call Group5. It's challenging to describe in a few words what type of images will work correctly in both of these formats, so this article will walk through the steps needed to prepare graphics for eink projects. What's inside of the file? One of the first challenges of working with any image file format is that each file format can support quite a long list of different types of data within it. The two main variables are bit depth and compression options. Bit depth is probably the most confounding issue because it can be hidden in plain sight. ...