Re: [cc65] The most critical operations of the C runtime

From: "Emanuele Fornara"; on Thursday, September 13, 2007; at 03:36 AM -0400
>
> As some of you might remember, I'm writing a 6502 Virtual Machine.
> I was thinking about accelerating the most critical routines
> of the C runtime.
> The idea is NOT to extend the CPU with custom opcodes,
> but to use the "IO" chip.
> Something like this:
>
> runtime_operation:
>   STA CC65OP1 ; operand 1, if necessary
>   STX CC65OP2 ; operand 2, if necessary
>   LDX #CC65_???
>   STX CC65OPC ; operation code; triggers operation
>   LDA CC65RES ; operation result, if necessary
>   RTS
>
> I have no access to the CPU registers; but, I have access to the memory,
> and I can assume a specific layout for page 0.  I cannot bloat the code
> of the "IO" chip too much; ideally, I'm looking for 5-10 operations to
> accelerate.

Obviously, the multiplication, division, and modulus subroutines can benefit
from a virtual co-processor.  Also, some of the more "complex" stack
routines could be moved into that "chip" -- the routines that do indexing
and indirect loads/stores.  They are used alot, to handle pointers, arrays,
and structures.

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