Tiny Programming Language In 25 Lines Of Code

January 22, 2018 by 9 Comments

There are certain kinds of programs that fascinate certain kinds of software hackers. Maybe you are into number crunching, chess programs, operating systems, or artificial intelligence. However, on any significant machine, most of the time those activities will require some sort of language. Sure, we all have some processor we can write hex code for in our head, but you really want at least an assembler if not something sturdier. Writing languages can be addictive, but jumping right into a big system like gcc and trying to make changes is daunting for anyone. If you want a gentle introduction, check out [mgechev’s] language that resides in 25 lines of Javascript.

The GitHub page bills it as a tiny compiler, although that is a bit misleading and even the README says it is a transpiler. Actually, the code reads a simple language, uses recursive descent parsing to build a tree, and then uses a “compiler” to convert the tree to JavaScript (which can then be executed, of course). It can also just interpret the tree and produce a numerical answer.

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MicroPython Learns A New Trick – ISP For AVRs

January 18, 2018 by 12 Comments

One of the reasons why the Arduino became so popular was the ability to program it with ease. It meant the end of big parallel programmers that would cost an arm and a leg. The latest installment of CircuitPython from [Lady Ada] and the team over at Adafruit is a library for programming AVR microcontrollers without a dedicated PC.

For the uninitiated, in-system programming or ISP for AVR controllers employ the SPI bus to write the compiled binary to the flash memory of the controller. The discount on the number of pins used itself is a benefit though getting the timings right was a bit tricky in the good old days. Most dedicated ISPs handle this nicely, though they are normally slaves to a host PC where an ‘upload’ button initiates the process.

With CircuitPython (a derivative of MicroPython), programming microcontrollers does not require going through the code-compile-flash cycle. It can be run on a number of processors, however, AVRs are not among them so this neat little library offers the next best thing. Wire-up an Atmega328P or ATmega2560 to a board like the ESP8266 that does run CircuitPython, and you can write firmware on the fly.

There is a complete tutorial on the subject thanks to [Phillip Torrone] and [Lady Ada] which includes some demo files for testing out the functionality. This opens up a lot of possibilities where OTA firmware updates for an AVR co-processor. We expect to see some keychain AVR programmers in the near future taking a hint from the ESP8266 based Two-Factor Authentication featured previously.

Write Your Own X86 Bootloader

October 23, 2017 by 40 Comments

What if you want to make a very lean machine and do without any operating system? Or maybe you want to try to write your own OS, even just for the challenge or fun? Maybe you were reading up on a cool OS architecture and thought to yourself, “I can write that!”. Well, before diving into your code, you’d first have to write something called a bootloader.

A bootloader is code that runs early on in a PC’s, Mac’s, Raspberry Pi’s or microcontroller’s boot sequence, before anything like an operating system is up. Often its job is to set up minimal hardware, such as RAM, and then load the OS or your embedded code.

[Alex Parker] has written a three-part series of clear blog posts that make writing the bootloader part easy, at least for x86 machines. And the nice thing is that you don’t need an x86 to get started. He does it on a Mac using the QEMU processor emulator, though he also talks about doing it under Windows and Linux.

In the first part of the series, the bootloader leaves you in the x86’s real mode, with 16-bit instructions and access to one megabyte of memory — think pre-80286 days, or 1982 for those of us who were computing back then. To prove it works, he uses BIOS calls to display “Hello world!”. This also shows that through the BIOS, you have a set of peripherals you can work with.

In the second part, he shows how to set up 32-bit protected mode and a Global Descriptor Table, making access to a large amount of memory easier.

In the first two parts, the code is written in assembly, so in the third part he finishes the series by showing how to load C++ code into memory and execute it. That C++ code would of course be your application, which we’ll leave to your imagination.

It’s reasonably rare to write bootloader code for a desktop computer — much less so for microcontrollers. For instance, [Dmitry Grinberg] wrote his own bootloader so that he could have encrypted ROM images for his AVR on USB. And we’ve talked about [Lady Ada]’s guide to burning Arduino bootloaders. But if you want to get down to the bare metal on your x86, the bootloader is the place to start. And it’s not so bad.

Save ESP8266 RAM With PROGMEM

March 10, 2017 by 21 Comments

When [sticilface] started using the Arduino IDE to program an ESP8266, he found he was running out of RAM quickly. The culprit? Strings. That’s not surprising. Strings can be long and many strings like prompts and the like don’t ever change. There is a way to tell the compiler you’d like to store data that won’t change in program storage instead of RAM. They still eat up memory, of course, but you have a lot more program storage than you do RAM on a typical device. He posted his results on a Gist.

On the face of it, it is simple enough to define a memory allocation with the PROGMEM keyword. There’s also macros that make things easier and a host of functions for dealing with strings in program space (basically, the standard C library calls with a _P suffix).

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MicroLisp, Lisp For The AVR

September 13, 2016 by 22 Comments

We’ve seen tiny microcontroller-based computers before, but nothing like this. Where the usual AVR + display + serial connection features BASIC, Forth, or another forgotten language from the annals of computer history, this project turns an AVR into a Lisp machine.

The μλ project is the product of several decades of playing with Lisp on the university mainframe, finding a Lisp interpreter for the 6800 in Byte, and writing a few lisp applications using the Macintosh Toolbox. While this experience gave the author a handle on Lisp running on memory-constrained systems, MicroLisp is running on an ATMega328 with 32k of Flash and 2k of RAM.  In that tiny space, this tiny computer can blink a few boards, write to an OLED display, and read a PS/2 keyboard.

The circuit is simple enough to fit on a breadboard, but the real trick here is the firmware. A large subset of Lisp is supported, as is analog and digitalRead, analog and digitalWrite, I2C, SPI, and a serial interface. It’s an amazing piece of work that’s just begging to be slapped together on a piece of perfboard, if only to have a pocket-sized Lisp machine.

Thanks [gir] for the tip.

Arduinos (and Other AVRs) Write To Own Flash

July 3, 2015 by 52 Comments

In this post on the Arduino.cc forums and this blog post, [Majek] announced that he had fooled the AVR microcontroller inside and Arduino into writing user data into its own flash memory during runtime. Wow!

[Majek] has pulled off a very neat hack here. Normally, an AVR microcontroller can’t write to its own flash memory except when it’s in bootloader mode, and you’re stuck using EEPROM when you want to save non-volatile data. But EEPROM is scarce, relative to flash.

Now, under normal circumstances, writing into the flash program memory can get you into trouble. Indeed, the AVR has protections to prevent code that’s not hosted in the bootloader memory block from writing to flash. But of course, the bootloader has to be able to program the chip, so there’s got to be a way in.

The trick is that [Majek] has carefully modified the Arduino’s Optiboot bootloader so that it exposes a flash-write (SPM) command at a known location, so that he can then use this function from outside the bootloader. The AVR doesn’t prevent the SPM from proceeding, because it’s being called from within the bootloader memory, and all is well.

The modified version of the Optiboot bootloader is available on [Majek]’s Github.  If you want to see how he did it, here are the diffs. A particularly nice touch is that this is all wrapped up in easy-to-write code with a working demo. So next time you’ve filled up the EEPROM, you can reach for this hack and log your data into flash program memory.

Thanks [Koepel] for the tip!

Embed With Elliot: Shifting Gears With AVR Microcontrollers

June 18, 2015 by 63 Comments

Most modern computers are able to dynamically adjust their operating frequency in order to save power when they’re not heavily used and provide instantaneous-seeming response when load increases. You might be surprised to hear that the lowly 8-bit AVR microcontrollers can also switch CPU-speed gears on the fly. In this edition of Embed with Elliot, we’ll dig into the AVR’s underappreciated CPU clock prescaler.

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