This firmware is intended to be a fully object-oriented highly modular control program for RepRap self-replicating 3D printers.
It owes a lot to Marlin and to the original RepRap FiveD_GCode. It was written by Adrian at RepRapPro Ltd.
General design principles
- Control by RepRap G Codes. These are taken to be machine independent, though some may be unsupported.
- Full use of C++ OO techniques,
- Make classes hide their data,
- Make everything except the Platform class (see below) as stateless as possible,
- No use of conditional compilation except for #include guards - if you need that, you should be forking the repository to make a new branch - let the repository take the strain,
- Concentration of all machine-dependent defintions and code in Platform.h and Platform.cpp,
- No specials for (X,Y) or (Z) - all movement is 3-dimensional,
- Except in Platform.h, use real units (mm, seconds etc) throughout the rest of the code wherever possible,
- Try to be efficient in memory use, but this is not critical,
- Labour hard to be efficient in time use, and this is critical,
- Don't abhor floats - they work fast enough if you're clever,
- Don't avoid arrays and structs/classes,
- Don't avoid pointers,
- Use operator and function overloading where appropriate.
- #defines are all CAPITALS_WITH_OPTIONAL_UNDERSCORES_BETWEEN_WORDS
- No underscores in other names - MakeReadableWithCapitalisation
- Class names and functions start with a CapitalLetter
- Variables start with a lowerCaseLetter
- Use veryLongDescriptiveNames
There are six main classes:
- Platform, and
This is just a container class for the single instances of all the others, and otherwise does very little.
This class is fed GCodes, either from the web interface, or from GCode files, or from a serial interface, Interprets them, and requests actions from the RepRap machine via the other classes.
This class implements all heating and temperature control in the RepRap machine.
This class controls all movement of the RepRap machine, both along its axes, and in its extruder drives.
This is the only class that knows anything about the physical setup of the RepRap machine and its controlling electronics. It implements the interface between all the other classes and the RepRap machine. All the other classes are completely machine-independent (though they may declare arrays dimensioned to values #defined in Platform.h).
When the software is running there is one single instance of each main class, and all the memory allocation is done on initialization. new/malloc should not be used in the general running code, and delete is never used. Each class has an Init() function that resets it to its boot-up state; the constructors merely handle that memory allocation on startup. Calling RepRap.Init() calls all the other Init()s in the right sequence.
There are other ancillary classes that are declared in the .h files for the master classes that use them. For example, Move has a DDA class that implements a Bresenham/digital differential analyser.
There is a single interrupt chain entered via Platform.Interrupt(). This controls movement step timing, and this chain of code should be the only place that volatile declarations and structure/variable-locking are required. All the rest of the code is called sequentially and repeatedly as follows:
All the main classes have a Spin() function. These are called in a loop by the RepRap.Spin() function and implement simple timesharing. No class does, or ever should, wait inside one of its functions for anything to happen or call any sort of delay() function. The general rule is:
Can I do a thing? Yes - do it No - set a flag/timer to remind me to do it next-time-I'm-called/at-a-future-time and return.
The restriction this strategy places on almost all the code in the firmware (that it must execute quickly and never cause waits or delays) is balanced by the fact that none of that code needs to worry about synchronization, locking, or other areas of code accessing items upon which it is working. As mentioned, only the interrupt chain needs to concern itself with such problems. Unlike movement, heating (including PID controllers) does not need the fast precision of timing that interrupts alone can offer. Indeed, most heating code only needs to execute a couple of times a second.
Most data is transferred bytewise, with classes' Spin() functions typically containing code like this:
Is a byte available for me? Yes read it and add it to my buffer Is my buffer complete? Yes Act on the contents of my buffer No Return No Return
Note that it is simple to raise the "priority" of any class's activities relative to the others by calling its Spin() function more than once from RepRap.Spin().