Re: Mixing virtual and real machine code in an interpreter

graham@pact.srf.ac.uk (Graham Matthews) writes:
>I am interested in the problem of mixing sections of real and virtual
>machine code. I have an interpreter for a language L that compiles L into
>a virtual machine code and executes this. For certain critical sections, I
>would like to compile into native assembler. I envisage having some sort
>of virtual machine instruction that jumps to a section of real machine
>instructions, and similarly a jump back ...


Just as a point of reference, or humor as the case may be. There was a
compiler company which created C and Pascal compilers for the TRS-80
(model I no less) which did exactly that.


  Most of the code the compiler generated was a P-code derivative, being
interpreted by an interpreted embedded in the program. However, with
certain compiler directives you could cause the P-code for certain
functions to be "compiled" into native Z-80 code.


  This worked with a simple P-code instruction indicating that the next
instruction was hardware. Similarly, they used some sort of
USER-interrupt-like mechanism to trap back into the interpreter when the
Z-80 instructions were complete.


- Dave Rivers -
(sastdr@unx.sas.com)
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