8bit Basic Virtual Machine - 8bit 1Address Instruction Set
author Neil Franklin, last modification 2008.10.30


design features

directly execute Basic code internal representation
  entire basic state inside processor, including FOR/GOSUB stack
  in external memory only semi-compiled basic tokens and variables
compiler for generating and listing internal is external
  and as such is written itsself in internal representation
  to enable this multiple contexts, with own set of line numbers and globals


registers

all registers and stack are internal, not programmer visible
  "program counter" is actually "current line counter", set by GOTO or RUN


memory

64k*8bit general purpose program and data memory, byte addressed
256*8bit separate IO space, only immediate addressing


program format

header line number 2byte binary followed by offset to next header
  offset allows fast search, but is position independant, no recalc
line tokens for command, operations, functions
  token+ascii for constants and vars
  token for end of line is also "header comment out" when interpreting
possibly also sorted bin-search table with linenumber to address mappings
  or do this as an runtime generated cache in the processor, invalidate?
lines allocated as an ream of code, or each line allocated on heap

variable space format

sorted bin-search table of names with value or pointer into heap space
  scalar numbers direct, array numbers and strings on heap