Writing Android Apps In C, No Java Required

Older Android devices can be had for a song, and in many cases are still packing considerable computational power. With built in networking, a battery, and a big touch screen, they could easily take the place of a Raspberry Pi and external display in many applications. As it so happens, Google has made it very easy to develop your own Android software. There’s only one problem: you’ve got to do it in Java.

Looking to get away from all that bloat and overhead, [CNLohr] set out to see what it would take to get 100% C code running on an Android device. After collecting information and resources from the deepest and darkest corners of the Internet, he found out that the process actually wasn’t that bad. He’s crafted a makefile which can be used to get your own C program up and running in seconds.

We mean that literally. As demonstrated in the video after the break, [CNLohr] is able to compile, upload, and run a C Android program in less than two seconds with a single command. This rapid development cycle allows you to spend more time on actually getting work done, as you can iterate through versions of your code almost as quickly as if you were running them on your local machine.

[CNLohr] says you’ll still need to have Google’s Android Studio installed, so it’s not as if this is some clean room implementation. But once it’s installed, you can just call everything from his makefile and never have to interact with it directly. Even if you don’t have any problem with the official Android development tools, there’s certainly something to be said for being able to write a “Hello World” that doesn’t clock in at multiple-megabytes.

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C#, The Language For All Platforms – Now Including Windows 3.11 And DOS

The Microsoft .NET framework has been with us in one form or another since the millennium, and though it has remained largely the preserve of the Microsoft universe, it has found its way since then through a variety of implementations to other platforms including MacOS and GNU/Linux. In Microsoft terms though its history goes back only as far as Windows 98, earlier MS operating systems remain off-limits.

Just a glimmer of .NET in DOS and Windows 3.11 comes courtesy of [Michal Strehovsk√Ĺ], who has successfully compiled .net C# code for both Windows 3.11 and DOS. An in-depth explanation comes courtesy of [Scott Hanselman], and it involves some tricks spanning the decades since the early 1990s. The .NET Core compiler’s object files can be fed into the linker that shipped with an ancient version of Microsoft’s C++ compiler, which when used with Microsoft’s Win32s compatibility layer that brought some of Windos NT’s APIs to the 16-bit OS, allows C# from 2020 to run as though it were 1992 again. Meanwhile the DOS version uses .NET Core’s ability to produce self-contained executables along with some very significant tricks to pare down the size of the finished program from many megabytes to an eventual DOS-suitable 27k. Remember the apocryphal Bill Gates quote, that “640k should be enough for anyone“, that refers to the maximum memory available to DOS without extra memory-extending tricks.

Neither piece of software is especially useful, and we can’t see a rush of C# coders to these new platforms. But we applaud him for his ingenuity, and getting old hardware to do new tricks is right up our alley. It’s certainly dredged up a few memories from back in the day for us. Meanwhile we’ve featured .NET in a few projects over the years, most recently on an FPGA.

Little Hex Tricks Make Little Displays A Little Easier

Depending on the device in hand and one’s temperament, bringing up a new part can be a frolic through the verdant fields of discovery or an endless slog through the grey marshes of defeat. One of the reasons we find ourselves sticking with tried and true parts we know well is that interminable process of configuration. Once a new display controller is mostly working, writing convenience functions to make it easier to use can be very satisfying, but the very first thing is figuring out how to make it do anything at all. Friend of Hackaday [Dan Hienzsch] put together a post describing how to use a particular LED controller which serves as a nice walkthrough of figuring out the right bitmath to make things work, and includes a neat trick or two.

The bulk of the post is dedicated to describing the way [Dan] went about putting together his libraries for a 7-segment display demo board he makes. At its heart the board uses the IS31FL3728 matrix driver from ISSI. We love these ISSI LED controllers because they give you many channels of control for relatively low cost, but even with their relative simplicity you still need to do some bit twiddling to light the diodes you need. [Dan]’s post talks about some strategies for making this easier like preconfigured lookup tables with convenient offsets and masking bits to control RGB LEDs.

There’s one more trick which we think is the hidden star of the show; a spreadsheet which calculates register values based on “GUI” input! Computing the bit math required to control a display can be an exercise in frustration, especially if the logical display doesn’t fit conveniently in the physical register map of the controller. A spreadsheet like this may not be particularly sexy but it gets the job done; exactly the kind of hack we’re huge fans of here. We’ve mirrored the spreadsheet¬†so you can peek at the formulas inside, and the original Excel document is available on his blog.

All You’ve Ever Wanted To Know About Compilers

They say that in order to understand recursion, you must first understand recursion. Once you master that concept, you might decide that it’s time to write your own compiler that can compile itself as a fun side project. According to [Warren] aka [DoctorWkt], who documented every step of writing this C compiler from scratch, a true compiler will be able to do that.

Some of the goals for the project included self-compiling, focusing on a real hardware platform, practicality, and simplicity. [Warren] outlines a lot of the theory of compilers as well, including all the lexical, grammar, and semantic analysis and then the final translation into assembly language, but really focuses on making this compiler one for practical use rather than just a theoretical implementation. He focuses on Intel x86-64 and 32-bit ARM platforms too, which are widely available.

This project is a long read and very thoroughly documented at around 100,000 words, so if you’ve ever been interested in compilers this is a great place to start. There are a lot of other great compiler tools floating around too, like the Compiler Explorer which shows you generated code as you write in a higher level language.

[via Hackaday.io]

Asynchronous Routines For C

[Sandro Magi] noted that the async/await idiom has become more prevalent in programming recently. According to him, he first encountered it in C# but has found examples of it in JavaScript and Rust, too. The idea is simple: allow a function to return but come back later to complete something that takes a long time. Of course, multithreading is one answer to this, but generally, this technique implies more of a coroutine setup where functions cooperate to some degree to get good behavior. [Sandro] took some ideas from the existing protothread library and used it to create a system to get this effect in C and, by extension, C++.

Adding this “library” is as simple as including a header file. All the magic occurs at the preprocessor and compiler. There’s no code to link. The async routines only need two bytes of overhead and — unlike proper threads — don’t need a preallocated private stack.

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Linux Fu: Shell Scripts In C, C++, And Others

At first glance, it might not seem to make sense to write shell scripts in C/C++. After all, the whole point to a shell script is to knock out something quick and dirty. However, there are cases where you might want to write a quick C program to do something that would be hard to do in a traditional scripting language, perhaps you have a library that makes the job easier, or maybe you just know C and can knock it out faster.

While it is true that C generates executables, so there’s no need for a script, usually, the setup to build an executable is not what you want to spend your time on when you are just trying to get something done. In addition, scripts are largely portable. But sending an executable to someone else is fairly risky — but your in luck because C shell scripts can be shared as… well, as scripts. One option is to use a C interpreter like Cling. This is especially common when you are using something like Jupyter notebook. However, it is another piece of software you need on the user’s system. It would be nice to not depend on anything other than the system C compiler which is most likely gcc.

Luckily, there are a few ways to do this and none of them are especially hard. Even if you don’t want to actually script in C, understanding how to get there can be illustrative.

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Lambdas For C — Sort Of

A lot of programming languages these days feature lambda functions, or what I would be just as happy to call anonymous functions. Some people make a big deal out of these but the core idea is very simple. Sometimes you need a little snippet of code that you only need in one place — most commonly, as a callback function to pass another function — so why bother giving it a name? Depending on the language, there can be more to it that, especially if you get into closures and currying.

For example, in Python, the map function takes a function as an argument. Suppose you have a list and you want to capitalize each word in the list. A Python string has a capitalize method and you could write a loop to apply it to each element in the list. However, map and a lambda can do it more concisely:

map(lambda x: x.capitalize(), ['madam','im','adam'])

The anonymous function here takes an argument x and calls the capitalize method on it. The map call ensures that the anonymous function is called once for each item.

Modern C++ has lambda expressions. However, in C you have to define a function by name and pass a pointer — not a huge problem, but it can get messy if you have a lot of callback functions that you use only one time. It’s just hard to think up that many disposable function names. However, if you use gcc, there are some nonstandard C features you can use to get most of what you want out of lambda expressions.

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