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8chips-assembly-simulator

roughly following along with / inspired by:

Contains:

  • An assembler for a byte code language
  • A simulator for a processor that runs the byte code language - with a very simple instruction set.
  • A UI for the simulator using imgui.net
  • A vm translator/implementation - which transpiles vm intermediate language into assembly.
  • some tests.

A register level simulator and verilog implementation of this cpu exits here: https://github.com/mjkkirschner/8chipsimulator

alt text

assembly language docs:

Instructions are 32 bit values. Operands are stored at the next location in memory. For example to load the a register with the value 10.

ram[0]: LOADA

ram[1]: 10

Values in this simulator (on this branch anyway) are internally stored as 32bit signed ints.

Originally this design supported only 16 bit unsigned numbers, and word width was 16 bits, but memory is cheap in a simulator... It's unclear if when synthesized, if this design (64k x 32bit memory) will fit in bitram on reasonable cost FPGAs.

valid instructions for the assembler:

  • NOP : spins for an instruction cycle - this simulator does not emulate clock cycles or execute microcode so this doesn't do much.

  • LOADA : Loads value at operand into A register. 1 operand.

  • OUTA : Loads the output register with the value in the A register.

  • ADD : ADD Adds the current value in the A register to the value stored at the memory location at operand. 1 operand.

  • SUBTRACT :

  • STOREA :

  • LOADAIMMEDIATE :

  • JUMP :

  • JUMPTOPOINTER :

  • JUMPIFEQUAL :

  • JUMPIFLESS :

  • JUMPIFGREATER :

  • LOADB :

  • LOADBIMMEDIATE :

  • STOREB :

  • UPDATEFLAGS :

  • HALT :

  • LOADCONTROLIMMEDIATE :

  • STORECOMSTATUS : Not implemented in simulator.

  • STORECOMDATA : Not implemented in simulator.

  • STOREAATPOINTER :

  • LOADAATPOINTER :

  • MULTIPLY :

  • DIVIDE :

  • MODULO :

  • AND :

  • OR :

  • NOT :

assembler features:

  • Labels - labels take the form (SOMELABEL) and designate a memory location. They can be used for jumps
(START)
JUMP
START
  • Symbols - symbols are alphaNumeric strings starting with a letter character and containing no spaces. These map to a memory location.
LOADA
someMemLocationSymbol

has the effect of loading whatever value is at someMemLocationSymbol into A

symbols can also be used with offsets.

LOADA
someMemLocationSymbol + 10

has the effect of loading whatever value is at someMemLocationSymbol offset by 10 memory addresses into A

you can also store a value at a symbol - this will be expanded to a simple macro of assembly code that will store the value at the memory location which the symbol points to.

someMemLocation = 10
LOADA
someMemLocationSymbol

has the effect of loading 10 into A.

  • Defines - defines add a symbol to the symbol table - but you can control the address. Think of it like a label for any memory address. Perhaps these should be called something else ;).

These have a form like:

#define importantSymbol 100

will create a symbol in the assembler symbol table at memory address 100 you can then use it like any other symbol.

vm language docs: