Friday, May 24, 2013

Peripheral Template Library - attempt to efficiently capture common microcontroller algorithms in C++

There were not many posts in this year, partly because I decided to concentrate on writing code and hacking things instead. One of the project I find myself hacking regularly during last half-year is a library modestly called Peripheral Template Library.

Ever since initial amazement with Arduino warn off, it became clear that while it provides concise and easy to use (to learn, to understand) API, it is to schematic, implemented too inefficiently, libraries have reuse, compatibility and configurability problems, and all those things are not portable across really wide MCU range and otherwise not production ready (because of all those efficiency, reuse, etc. issue), but rather a toybox.

Trying to implement things without Arduino overhead, there was growing dissatisfaction with the need to slash code when moving from one MCU to another (due to economical and availability issues, or plain for creative reasons). It became clear the need to abstract things away, but without losing efficiency. The only way to achieve that is metaprogramming. As nowadays nobody writes MCU software in LISP, I turned to C++ - after almost 10 years break I guess.

Many embedded programmers shrug at C++, and well, I did that for any C++ at all for quite some time. But modern C++ is not that "object-oriented syntactic sugar" which your old Turbo C++ 1.0 was (yeah, last one which could run on your old XT, because 2.0 required 286 and protected mode memory extender). Modern C++ is multi-paradigm language, of which "runtime" "object orientation" is just small part. The core part is however compile-time type-based metaprogramming template engine, that's something which allows to achieve aforementioned abstraction/efficiency ratio (and we don't talk here about "C" efficiency here, but something closer to Assembler level).

That's how PTL was born. The idea was to wrap the most core part of any MCU - GPIO (General Purpose Input/Output), and on top of it implement support for standard communication protocols - UART, SPI, I2C, 1-Wire, etc. Everything implemented as templated classes, so can be easy specialized to use hardware blocks of particular MCU. Generalized cross-MCU was one of top goals from the start, i.e. more attention was given to design and implementation of classes which capture basic MCU functionality which is available in any MCU, rather than adhoc peculiarities of particular MCU. The latter can be wrapped too of course - on demand.

Past GPIO and communication protocols, handling timers and delays was second goal. Support for CPU-based delay - both (perfect-cycle) static and dynamic was implemented, then basic timer interface was added, with delay on top of it, with all 3 kinds of delays providing the same interface and thus fully replaceable and combinable.

What comes out of it is available at . MSP430, AVR, STM32 and EFM32 are supported (all to the different level though, but the basic functionality as described above is available for all by now). The grand aim is to design framework to support all possible (and impossible) MCUs ;-).

There're still log of refactors to do and functional block of individual MCUs to wrap. Some aspects, like clock tree management needs more though and design. Then, there's a need to add bindings/drivers for specific devices, I did that for few already, but of course that's area where I won't be able to compete with existing code, so I'm looking into finding good codebases to port.

License-wise, Peripheral Template Library is released under LGPL3 license, but I'm already thinking about adding linking exception and/or switch to BSD-like license altogether.

Here's a usual LED blinker example:

#include <gpio.hpp>
#include <cpu.hpp>
#include <board.hpp>
#include <delay_static.hpp>
#include <delay_time.hpp>

using namespace PTL;

typedef TimeDelay<board::freq, StaticDelay> delayer;

int main()
    while (true) {

This will compile and work out of the box on any of supported boards - specific LED to use (board::LED) is configured in board config header.

Let me know what you think about PTL. For me, it's definitely exciting, innovative area - not many libs provide such efficient support with such wide heterogeneous coverage, and you really do architecturing and design here, not just dumb boring code. (I admit that partly PTL effort is driven by dissatisfaction of technical inefficiencies, imperfection and warts in "one level bigger" Linux world.)

Saturday, May 18, 2013

Links for May 2013

I didn't post "Links" topics for a while - that's of course not because there're no interesting projects around, but because there're too many and you can't keep up with them ;-). Anyway, not collecting links to them doesn't help either, so:

  • openFrameworks - C++ framework to glue together ~20 well-known technologies and libraries, mostly for visualization, UI and multimedia (all collectively "creative arts coding")
  • Cinder - Another C++ contender from the similar area
  • Emscripten - "An LLVM-to-JavaScript Compiler" (C, C++ compilation to JavaScript)
  • asm.js - "An extraordinarily optimizable, low-level subset of JavaScript", from Emscripten authors.
  • "List of languages that compile to JS"- from CoffeeScript authors.