A 16-bit ALU implemented in Minecraft
Sep 29th, 2010 by dholm


This is an amazing video demonstrating a fully working 16-bit ALU implemented in the seminal online game Minecraft.

Tumblelog 100929
Sep 29th, 2010 by dholm

fastdep, a faster (than gcc -MM) C/C++ dependency generator.

HOWTO: Build an RT-application, hard realtime using the Linux real-time preemption patch.

The main control room at ESA's European Space Operations Centre in Darmstadt (Photo credit: ESA, 2002)

Eigen, is a linear algebra package for C++ relying on templates to provide syntactic sugar.

The typename Keyword, is used to weed out ambiguity in C++ templated code.

vasm portable and retargetable assembler, supporting many architectures and syntax flavors.

The Atari ST, Part 1, Part 2, a history of the creation of this classic computer.

Stamp-Controlled High Power H-Bridge and H-bridge secrets part 1, good analysis on how H-bridges works and the intricacies involved.

Introduction to NEON on iPhone, a good introduction to assembly and intrinsic NEON programming on the ARM.

Coding for NEON – Part 1: Load and Stores, dive deeper into the world of NEON programming by some useful examples with very good explanations.

strlcpy and strlcat – consistent, safe, string copy and concatenation., improves strncpy and strncat in order to provide more secure implementations.

Tumblelog 100916
Sep 16th, 2010 by dholm

UTF-8 history, provides the correct history of UTF-8 and its creation.

ARM GCC Inline Assembler Cookbook, provides details on how to specify registers etc for the ARM architecture.


BareMetal OS, an operating system for x86-64 written entirely in assembly.

PCD – Process Control Daemon, a process monitoring facility for embedded systems which offers fine grained process control.

Giottto, a state machine for scheduling periodic tasks with hard realtime requirements.

sigslot – C++ Signal/Slot Library, based on Qt sigslot offers a light weight library for implementing events.

RouterStation Pro, is an open hardware platform for building your own router.

Modded Nintendo Lets You Play Mario With Your Eyes, even if your motor skills are impaired.

Wipeout recreated with an RC car and lots of cardboard, when computer games cross over into the real world.

Optimisations of AVR programs using avr-gcc, offers recommendations on how to optimize your AVR code and avoid common performance pitfalls.

Tumblelog 100712
Jul 12th, 2010 by dholm

Electronic Component Coaster Set, coasters for the geeks in all of us. See how many drinks it will take for you to prototype something truly amazing with them.

disassembled household appliances, see the insides of all the regular household appliances.

Please help me find the original source

Personalities by ?

Making a Nintendo SNES controller into bluetooth; using an MSI BGP100, as I’ve been a SNES fan for many a year this goes onto this years wish lists.

Eternal September, free NNTP access for everyone! No more talking to tech support who never heard of anything other than http

Starring the Computer, provides us with a comprehensive list of computers showing up in movies along with freeze frames and everything. Help make the site even more complete.

MathOverflow, yet another projekt from the StackOverflow guys, guess what it’s for. Still, it’s a good concept and their system is sound.

Two Teeny Tiny Fonts, are two extremely small but still readable fonts. Sadly only screenshots are provided as of yet.

“Reply-To” Munging Still Considered Harmful. Really., interesting read if you are into SMTP.

Jul 7th, 2010 by dholm

I decided to start a category for iPod/iPhone/iPad/iWhatever apps since I now have so many and want to share my recommendations. This will be my first post.

By about now everyone should have heard about geocaching, if not you really should read up on it.

My first iPhone application recommendation is Geocaching by Groundspeak Inc..

Tumblelog 100614
Jun 14th, 2010 by dholm

The Hercules System/370, ESA/390, and z/Architecture Emulator, an emulator for the aforementioned systems.

Ubunchu, Ubuntu Manga in English, is a manga about Ubuntu. This is great stuff, check it out,

HP Sauce

DRBD, provides a block device for high availability data clusters.

Digital: A Love Story, become an oldschool cracker and learn the story about Digital along the way.

Fritzing, an open source tool for researchers and hobbyists to create PCBs.

Joe’s Blog: An into to modern OpenGL., a brief but great overview of OpenGL’s inner workings.

Taligent’s Guide to Designing Programs, provides a great object-oriented design system.

Miegakure, is a four dimensional in the works. platformer

Pure C++ Options Classes, how to implement optional arguments using pure C++-

USB Performance Monitor, build a performance monitor using the oh so classic VU meters.

Binding C++ to Lua, Part 2; Binding Our First Class
May 23rd, 2010 by dholm

This part will be rather short and summarize part one by providing a very simple sample using our Luna implementation.
Let’s begin by creating a very simple class which we call Test along with a Lua binding LuaTest which will be the intermediate between C++ and Lua.

#include <iostream>

#include "Luna.hpp"

class Test {
    Test(int x) : m_x(x) { }
    int getValue() const { return m_x; }
    int m_x;

The test class is a simple getter that provides a method, getValue, which will return the value set in the constructor.
In order to make this class available from Lua we need to write a binder class which translates to and from C++ and Lua code, called LuaTest for the sake of simplicity.

class LuaTest {

LUNA_TYPES(LuaTest); is a simple macro which injects the class with a couple of placeholder variables used by Luna.

LuaTest(lua_State* l) : m_test(luaL_checknumber(l, 1)) { }
    LuaTest(int x) : m_test(x) { }

We need to set up two constructors, one for Lua and one for C++ which emulates the same functionality as the C++ version. The C++ constructor for LuaTest is pretty straightforward but the Lua version is a bit more tricky.
All Lua calls only take a pointer to the actual Lua state since all values are pushed and pulled onto the stack. in this case we use luaL_checknumber(l, 1). This function call will return the first element on the top of the stack assuming it’s a number otherwise it will trigger an error.

int getValue(lua_State* l) {
    lua_pushnumber(l, static_cast<double>(m_test.getValue()));
    return 1;

This time we use lua_pushnumber(l, static_cast<double>(m_test.getValue())); to get the value from the stored Test object instance. Not that all numbers in Lua are in double so we need to cast them when expecting something else.

    Test m_test;

LUNA_CLASS(LuaTest, Test, Test) = {
    LUNA_METHOD(LuaTest, getValue),

The LUNA_CLASS macro is used to register the class along with exposing methods calls, if any, the list has to be terminated with a {0}. The first argument to LUNA_CLASS is the name of the binding class, the second the actual C++ class name and the last the identifier to be used from Lua scripts. This way you can for instance bind a boost class to Lua like: LUNA_CLASS(LuaDate, boost::gregorian::date, Date)

int main(int argc, char** argv)
    lua_State* l = lua_open();
    luaL_dofile(l, argv[1]);
    return 0;

We create a very simple main function, compile it and pass it the following Lua code:

test = Test(1)
print("Test=" .. test:getValue())

The resulting output is left as an exercise to the reader.

In the next installment I will move on to some more advanced features such as instantiating specific C++ classes from within Lua scripts.

Binding C++ to Lua, Part 1; The Basics
May 8th, 2010 by dholm

I have been working on binding C++ to Lua and found that even though there are some good samples available on the lua-users wiki none of them really offers a complete or clean implementation except for Luabind which requires a lot of Boost components which might be unsuitable for embedded systems. Since I’ve never worked with Lua before this proved to be a good project to learn the rules and inner workings of the language.

If you haven’t worked with Lua before please read chapter 3 of the Lua 5.1 Reference Manual which provides a good introduction to the Lua C API. It’s important to understand that Lua is stack based and you work by pushing and popping values on and off the stack. In this first part I will show how to register a C++ class with Lua so that it can be instantiated and used from within a Lua script. This part is already well covered in LunaWrapper but I will attempt to break it down and explain each part.

Think of a Lua table as a sort of std::map to use C++ jargon. Class definitions in Lua live inside what is known as a metatable. The metatable is a table for which it is possible to modify the behavior of certain operations such as common binary operators and indexing. We need to use the metatable in order to let Lua know how to create and destroy C++ objects as well as binding object instances to method calls.

Enough talking, let’s have a look at some code. I will start out with how to set up the metatable and register your C++ class with it.

int methods = lua_gettop(l);

Create a new standard table in which we will store our class’ methods and save the index to it. Remember that Lua is stack based and we need to remember the indices of created variables if we need to reference them later. lua_gettop will return the absolute index of the item at the top of the stack, in this case the newly created table.

luaL_newmetatable(l, T::s_className);
int metatable = lua_gettop(l);

Create the metatable for our class and name if after our class (T::s_className).

lua_pushstring(l, T::s_className);
lua_pushvalue(l, methods);
lua_settable(l, LUA_GLOBALSINDEX);

Lua has three types of environments into which you can put values. We will put our our class metatables into the global environment in order to make the type available to all parts of our scripts. You can read about environments in chapter 2.9 of the reference manual.

We push the class name onto the stack followed by the index of our table of methods, which we will fill later. By calling lua_settable we tell Lua to store the method table in the global environment at the key “T::s_className“. In C++-speak this would be equal to having a std::map GLOBALSINDEX and doing GLOBALSINDEX[T::s_className] = methodArray;

lua_pushliteral(l, "__metatable");
lua_pushvalue(l, methods);
lua_settable(l, metatable);

Sets the metatable at the metatable stack index as the metatable of our method table. Meaning that Lua will now look for meta functions in “metatable” when calling methods from our method table.

lua_pushliteral(l, "__index");
lua_pushvalue(l, methods);
lua_settable(l, metatable);

Set up the indexing method of our metatable to get its values from the methods table. This will allow Lua to look for methods in the methods table whenever a call is made to the metatable (the class).

lua_pushliteral(l, "__gc");
lua_pushcfunction(l, gcT);
lua_settable(l, metatable);

Register a garbage collector for the metatable. Here we use lua_pushcfunction to let Lua know that whenever an instance of our class’ goes out of scope the function gcT should be called to clean up the object. This will allow us to execute our objects destructor and avoid any nasty resource leaks.

int methodTable = lua_gettop(l);
lua_pushliteral(l, "__call");
lua_pushcfunction(l, newT);
lua_pushliteral(l, "new");
lua_pushvalue(l, -2);
lua_settable(l, methods);
lua_settable(l, methodTable);
lua_setmetatable(l, methods);

In order for us to be able to create class instances in Lua we have to let Lua know how to instantiate a class. That is done by registering a C function, newT, which is called whenever someone performs a “function call” using our class name. You would recognize this as T::s_className().

Create a method table methodTable, set the function call to dispatch to the C function newT, which we will define later, and link it to the metatable of our table of methods.

In order to link methods names with the actual methods we need to set up a type to map them. Lets create a struct containing the name and a method type.

typedef int (T::*Method)(lua_State* l);

typedef struct {
    const char* name;
    Method method;
} MethodMap;

Note that we cannot bind our regular C++ classes directly to Lua. We will need an intermediate since it has to be able to marshall data to and from Lua. Since all arguments are marshalled each method call only needs to know which Lua state to push and pop data to. Our method calls will therefore only need a pointer to the Lua state and return the number of values it has pushed onto the stack.

for (MethodMap* m = classMethods; m->name; ++m) {
    lua_pushstring(l, m->name);
    lua_pushlightuserdata(l, reinterpret_cast<void*>(m));
    lua_pushcclosure(l, thunk, 1);
    lua_settable(l, methods);

For each method of our class we have to put the method map into the methods table together with a thunk as a C closure so that the object instance of the callee is passed to the method.

lua_pop(l, 2);

Finally pop the methods and class metatable off the stack and we’re done!

Ok, this wasn’t all that hard as long as you understand the stack concept. But we are missing a couple of things, the constructor, destructor and thunk so let’s move on and define them as well.

We need a type to store the pointer to our class instances in. Using Lua-speak we call them user data so we define a struct Userdata for them.

typedef struct { T* pT; } Userdata;

Now we need a “constructor” that creates instances of our objects.

int newT(lua_State* l) {
    lua_remove(l, 1);
    T* obj = new T(l);
    Userdata* ud = reinterpret_cast<Userdata*>(lua_newuserdata(l, sizeof(Userdata)));
    ud->pT = obj;
    luaL_getmetatable(l, T::s_className);
    lua_setmetatable(l, -2);
    return 1;

Remove the item at the top of the stack which is the name of the method call, “new“, which we already know since we have linked this specific function to that call. Create a new object of type T followed by a userdata entry in Lua into which we will put the pointer to our object. Get the metatable associated with the class name of T and connect it with our userdata so that Lua will use the data from our class metatable when working with our object instance. Return one to let Lua know that we put one item at the top of the stack, our object instance.

static int gcT(lua_State* l) {
    Userdata* ud = reinterpret_cast<Userdata*>(lua_touserdata(l, 1));
    T* obj = ud->pT;
    delete obj, obj = NULL;
    return 0;

This is the garbage collector for our class type. It will fetch the object instance from the top of the stack and call the C++ delete operator on it. Since we didn’t put anything on the stack this function returns zero.

int thunk(lua_State* l) {
    T* obj = reinterpret_cast<Userdata*>(luaL_checkudata(l, 1, T::s_className))->pT;
    lua_remove(l, 1);
    MethodMap* m = reinterpret_cast<MethodMap*>(lua_touserdata(l, lua_upvalueindex(1)));
    return (obj->*(m->method))(l);

Those of you who have ever written object-oriented code in a non object-oriented language will know that the first argument to a “method call” usually is a pointer to the object instance and that is the way it is done in Lua as well. We use luaL_checkudata to get the value at the top of the stack and verify that it is of userdata type. This call will actually return NULL if the item at the top of the stack isn’t of userdata type so we should check the return value but in order to cut down the code for the sake of this post I decided to trim out that particular check. lua_remove will remove the specified number of items from the top of the stack, in this case we remove the userdata from the top so that only the method arguments remain when we make the dispatch.

Since thunk is a C closure we can use lua_upvalueindex to get the method map from the methods table and use that to find out which method was being called. We return the result of the method call which again must be the number of items the method has pushed onto the Lua stack.

This concludes the first part of this series. In the next one I will show you how to use this code to register and use a simple C++ class from within a Lua script.

Luna source code, part 1

Tumblelog 100506
May 6th, 2010 by dholm

HOWTO: Run a Virtual Machine at Boot, a guide on how you can set up VMware Fusion to automatically launch virtual machines on bootup without logging in.

iSCSI and ZFS, how to get them to play together on FreeNAS.



muLinux, is a Linux distribution for really old PC computers.

Small Kernel Project, aims to develop a Linux kernel with minimal RAM and system requirements. It is mainly intended to run on x86 machines with less than 5MB of RAM.

Ukelele, is a tool to modify the keyboard layout in MacOS X.

Codezero, is a L4 microkernel with hypervisor support.

BeRTOS, a real time operating system for embedded platforms

Tumblelog 100222
Feb 22nd, 2010 by dholm

Awesome C64 visual debugger, ICU64 is a visual debugger for the C64 with live code introspection and break and continue style editing.

Playstation 3 Slim Teardown, it’s the usual teardown of expensive hardware I wish I owned.

Being Tired by David Holm

Being Tired by David Holm

The diskette that blew Trixter’s mind, a 25 year old hack to make a floppy bootable on two different platforms without flipping it over.

Lua/C++ interface, a simple yet effective Lua C++ wrapper.

The illustrated guide to recovering lost commits with Git, if you ever accidentally made a mistake with Git and don’t feel like doing all your work over again go here for some help.

Opinion: The unspoken truth about managing geeks, how you should be doing it.

Ragel State Machine Compiler, Ragel is a state machine language which will compile your state machine into a number of different languages making it easier to maintain your machines while still being able to use your favorite language.

google-styleguide, contains among other things a C++ lint tool for the Google C++ guidelines.

25 Microchips That Shook the World, yet another trip down memory lane worth taking.

libcpu, is a portable, drop in, CPU emulator library with support for a growing number of architectures. The backend is LLVM but each CPU has its own frontend.

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