mk8.nim

# mk8: mk7 with stack and memory addressing

import strformat
import vimes/sio
import vimes/load
import bench

include mk8_opcodes
include mk8_opnames
type Word = int16

var pc: Word # program counter
var sp: Word # stack pointer
var acc: Word # accumulator
var cc: int64 # cycle counter
var mem:   seq[Word] = @[] # memory
var code:  seq[Word] = @[] # program
var stack: seq[Word] = @[] # return stack

proc reset(quick=false) =
    pc=0; acc=0; cc=0
    if quick: return
    for j in low(mem)..high(mem):
        mem[j] = 0

proc trace(op,a:Word) =
    let opname = opnames[cast[Instr](op)]
    let va = mem[a]
    stderr.write_line """| {cc:3} | {pc:2} | {opname:>4} {a:2} | {acc:3} | {va:3} | """.fmt

proc debug() =
    echo "pc:", pc, " acc:", acc, " cc:", cc

proc run() =
    while true:
        let opc = code[pc]
        let op = cast[Instr](opc)
        let a = code[pc+1]
        
        when defined(cc):    cc+=1
        when defined(trace): trace(opc,a)

        pc += 2
        case op:
            # control flow
            of JZ:
                if acc==0: pc=a
            of JN:
                if acc<0:  pc=a
            of JMP: pc=a
            # data transfer
            of LDA:  acc = mem[a]
            of LIT:  acc = a # EXTENSION
            of STA:  mem[a] = acc
            # alu
            of ADD:  acc += mem[a]
            of SUB:  acc -= mem[a]
            of INC:  mem[a] += 1
            of DEC:  mem[a] -= 1
            # stdio - TODO: as extension
            of OUT: echo acc # stdout.write $acc & " "
            of IN:  acc = sio.read_int().Word
            # misc
            of HLT: return
            # MK8
            of CAL: stack[sp]=pc; sp+=1; pc=a
            of RET: sp-=1; pc=stack[sp]
            of LPA: acc = mem[mem[a]]
            of SPA: mem[mem[a]] = acc
            of ASR: acc = ashr(acc,a).Word
            of NOP: discard
            # EXTENSION
            of JP:
                if acc>0: pc=a
            of PUSH: mem[a]+=1; mem[mem[a]]=acc
            of POP:  acc=mem[mem[a]]; mem[a]-=1
            # EXTENSION 2
            of JZP:
                if acc>=0: pc=a
            of JZN:
                if acc<=0: pc=a
            # EXTENSION 3
            of LPAO:
                b = code[pc]; pc+=1
                acc = mem[mem[a]+b]
            of SPAO:
                b = code[pc]; pc+=1
                mem[mem[a]+b] = acc
            else:
                quit("unknown opcode op:" & $op, 1)

include cli
if is_main_module:
    cli()