User's Manual

HARSFEN0602
7 The Virtual Machines
7.1.1 Introduction Alla please complete where necessary
The Harmonica can run a user program, as explained in the Chapter "The Harmonica User Programming
Language". Although the user program runs syntactically the same statements as the interpreter, the
processing mechanism is totally different.
The interpreter analyses text on line. The user program does not – it runs a compiled code. The most
important advantage is that all the text analysis can be spared in real-time, boosting the user program
performance. Another advantage is that future user syntax improvements are possible without upgrading the
amplifier software.
An external tool, called "The Harmonica Compiler" compiles the user text. The compiler outputs a file of
short and simple binary commands.
Take for example the user text
DC=AC+1000;
This code is translated to
.... Alla please fill.
The texts of the compiled version above are in a mnemonic form. Each mnemonic represents an opcode of
fixed structure, as described below. In hexadecimal form, the example piece of code is
.... Alla please fill.
The compiled code looks much like an assembly language. The "CPU" that runs this assembly language is
written in DSP software. This software that implements the "User Program CPU" is called a "Virtual
Machine".
A virtual machine behaves much like a CPU – it has a stack, a code segment with program counter, and a
data memory segment.
The Harmonica is designed with multiple virtual machines, so that several user programs may be run in
parallel.
The machines are not completely similar. Only one machine, called the Main machine, is interrupted by
automatic routines. The other machines are not interrupted by automatic routines. If one desires to interrupt
another machine, he may write a software interrupt to that machine from the automatic routine handler of the
main machine.
The first release allows the user to activate only one (the Main) virtual machine.
7.2 Virtual Machine registers
A virtual machine has the following registers:
Register Description Comment
SP Stack pointer Points to top of stack.
BP Base pointer Freezes the value of the stack pointer
when a function is entered. BP is
used to refer local variables of a
function.
PC Program counter Points to the code position now
executing.
7.3 Call Stack During Function Call
Consider a call stack during a function call (the opcode is USRSUBJ).
Assume that a user defines a function :
function [float x, float y, float z] = f (int a, int b, int c, ind d) ; % Prototype
Assume that a function call is: