This is a (partial) emulation of a BBC Micro in Python - it includes emulation of a 6502 CPU and enough supporting hardware to boot MOS 1.2 and get to the BASIC prompt.
The emulator is intended for experimentation and learning about the operation of a simple CPU, within a wimpler Python environment. The emulator has the ability to 'hook' addresses within the 6502 code and either trace their use, or modify the behaviour, in Python.
The emulator can be run with python RunBeeb.py. This will start the emulator
running, booting the BBC MOS and entering BBC BASIC. The emulator provides
default hooks to allow the terminal input to be passed to the keyboard reading
code, VDU output will be written to the terminal output.
Simple hooks are provided for the filesystem interfaces, allowing access to files within the current working directory in the host system.
Within the emulator, running BASIC, you can write programs and load and save files. There is no video or sound system attached in this emulation, so any graphics will not be displayed, and sound (other than the terminal beeb) will not be heard.
The emulator runs at a BASIC prompt by default, and you can run commands, such as printing messages:
PRINT "Hello world"
The current directory can be listed with *CAT or *.:
*cat
Programs can be loaded and saved with LOAD and SAVE. On the BBC file paths
are separated by a . character (not the / that you might be used to on
unix-like systems, or the \\ used by Windows and DOS systems). An example
program can be found in the tests directory, which you can run:
LOAD "Tests.helloworld"
RUN
To quit the emulator, use *QUIT:
*quit
Extensions to the BBC system are provided through hooks which can be registered with the emulator. The emulation system, and its hooks, are based around the spirit of the Unicorn engine emulator. Hooks can be registered for code execution, and memory accesses.
The RunBeeb.py tool contains commented out code which can be enabled to use
these hooks directly. The example hooks allow code to be traced - each instruction
executed will be disassembled and displayed - and to report on memory accesses
in different areas of memory.
The pybeeb.Host package contains a number of implementations of hooked routines
which can be used to replace or augment the standard MOS routines. This package
contains base classess which interpret the interfaces in the base module, and
concrete classes within the hostfs and hosttty modules. These latter modules
provide the file system and terminal I/O.
The RunBeeb.py tool includes two simple examples of these extensions, to provide
more information in *FX0 (the system version), and to allow the emulator to be
quit with *Quit.