| Author: | Dean Hall |
|---|---|
| Id: | PyMiteOverview.txt 133 2006-12-05 20:38:15Z dwhall |
This document gives an overview of PyMite the software and the project that develops it. In doing so, it helps the newcomer understand the scope of the project and intended purpose of the software.
PyMite is a flyweight Python interpreter written from scratch to execute on 8-bit and larger microcontrollers with resources as limited as 64 KiB of program memory (flash) and 4 KiB of RAM. PyMite supports a subset of the Python syntax and can execute a subset of its bytecodes. PyMite can also be compiled, tested and executed on a desktop computer.
PyMite is targeted toward microcontrollers with limited program and random access memories. In order to operate in this embedded environment, PyMite has to sacrifice some features found in desktop Python. However, the author feels that enough of Python's core abilities are present in PyMite to call PyMite a flyweight Python interpreter rather than a Basic-like language with Python syntax.
With Python's reputation for being friendly to beginning programmers, PyMite should appeal to those who are programming microcontrollers for the first time. For those familiar with Python, PyMite should provide a rapid development environment. And for those with Python and C or assembly experience, PyMite's Native Function interface provides a powerful way to embed low-level code in a PyMite function. In short, PyMite has something for all levels of programmers.
Python is a language that is easy to learn. PyMite is just as easy to learn, if not more so because there is less to learn. This should allow brand new and novice programmers a straightforward path to writing code for a microcontroller. The entry-level programmer, though, will have to wait until PyMite is ported to the microcontroller that they are using. By this, I mean, that in order to use the pins and peripherals of a specific microcontroller, a C or assembly code library must be written to interface PyMite to that microcontroller. Atmel's AVR family of 8-bit microcontrollers are a favorite of PyMite's lead developer and will likely have the necessary interface library available soon. Atmel's ARM7TDMI family, a.k.a. the SAM7 family, is also a lead candidate for an early porting interface.
PyMite supports the important datatypes an experienced Python programmer expects: 32-bit signed integers, Strings, Tuples, Lists and Dictionaries (a.k.a. Dicts, Hashes and Maps). PyMite also supports the basic flow control statements and logic statements. Even some of Python's more advanced features such as generators, classes and decorators are supported. See PyMiteFeatures for a detailed description of what PyMite supports. Suffice to say, PyMite has enough to keep you busy.
PyMite would not be complete without a way for the Python application code to call low-level routines to access the special features of a microcontroller. PyMite provides this advanced feature called Native Function and has a slick and easy way to implement them. Native Functions are written by defining a function in Python code with the keyword pass as the function's body, but inserting C code in the function's documentation string. Macros are provided to access the PyMite stack and arguments to the function. Within the C code, the developer may write assembly code using the asm() statement if desired. The context switch overhead to call a Native Function is near that of calling a function from within C. This fast and convenient interface between Python code and C code provides the advanced developer a means to access the low-level features of the microcontroller and PyMite itself.
The PyMite project is hosted at http://pymite.python-hosting.com. The latest PyMite release is available for download from that site. The site also explains how to obtain the latest development version of PyMite via the Subversion source code management tool.
PyMite does not have a set schedule for releases. The current system is to make a release when a significant set of changes have been mainlined and a fair set of tests has shown the changes to be working to some degree. The determination of "significant" is up to the lead developer.
http://pymite.python-hosting.com is a Trac site which serves as the center for PyMite development. The latest PyMite release is available for download from that site. The user should be familiar with how to manipulate .tar.gz files.
PyMite comes as a source distribution only. The user will have to install a cross-compile toolchain in order to build PyMite for a target device. PyMite uses a Makefile system and the GCC toolchain by default to build the PyMite library file. The user is also responsible for writing a main() function in C, compiling that to an executable and downloading it to the microcontroller. Sample projects are provided.
If PyMite does not support your needs now, join the PyMite discussion list to make your desire known and help make it happen.