EmbedVM - Embedded Virtual Machine
==================================

EmbedVM is a small embeddable virtual machine for microcontrollers with a
C-like language frontend. It has been tested with GCC and AVR microcontrollers.
But as the Virtual machine is rather simple it should be easy to port it to
other architectures.

The VM simulates a 16bit CPU that can access up to 64kB of memory. It can
only operate on 16bit values and arrays of 16bit and 8bit values. There is
no support for complex data structures (struct, objects, etc.). A function
can have a maximum of 32 local variables and 32 arguments.

Besides the memory for the VM, a small structure holding the VM state and
the reasonable amount of memory the EmbedVM functions need on the stack there
are no additional memory requirements for the VM. Especially the VM does not
depend on any dymaic memory management.

EmbedVM is optimized for size and simplicity, not execution speed. The VM
itself takes up about 3kB of program memory on an AVR microcontroller. On an
AVR ATmega168 running at 16MHz the VM can execute about 75 VM instructions
per millisecond.

All memory accesses done by the VM are parformed using user callback functions.
So it is possible to have some or all of the VM memory on external memory
devices, flash memory, etc. or "memory-map" hardware functions to the VM.

The compiler is a UNIX/Linux commandline tool that reads in a *.evm file and
generates bytecode in vaious formats (binary file, intel hex, C array
initializers and a special debug output format). It also generates a symbol
file that can be used to access data in the VM memory from the host
application.

The file README.VM contains a brief description of the virtual machine.

A documentation of the high level language frontend is still to be done.

The directory tools/ contains a compiler for the C-like EVM lagnuage that
can be used for generating VM bytecode in various formats.
See tools/example.evm for a simple demo application.

The directory vmsrc/ contains the virtual machine itself and a simple demo
host application as a reference for how to embedd the VM.

The directory examples/ contains example applications using EmbedVM.