8bitworkshop/test/unit/teststepover.ts

import assert from "assert";
import { describe, it } from "mocha";
import {
  BaseDebugPlatform,
  CpuState,
  EmuState,
} from "../../src/common/baseplatform";
import { disassemble6502 } from "../../src/common/cpu/disasm6502";

// Minimal 6502-ish platform for exercising BaseDebugPlatform.stepOver().
// readAddress() relies on 'this' like real platforms (e.g. c64.ts), so it
// catches bugs where the method reference is detached from its object.
class TestStepPlatform extends BaseDebugPlatform {
  mem = new Uint8Array(0x10000);
  cpu = { PC: 0, SP: 0xff };
  paused = false;

  getPC(): number { return this.cpu.PC; }
  getSP(): number { return this.cpu.SP; }
  getCPUState(): CpuState { return { PC: this.cpu.PC, SP: this.cpu.SP }; }
  isStable(): boolean { return true; }
  // uses 'this' -- must not be called unbound
  readAddress(a: number): number { return this.mem[a & 0xffff]; }
  // like real platforms, goes through the passed-in read callback
  disassemble(pc: number, read: (a: number) => number) {
    return disassemble6502(pc, read(pc), read(pc + 1), read(pc + 2));
  }
  saveState(): EmuState { return { c: { PC: this.cpu.PC, SP: this.cpu.SP } }; }
  loadState(state: EmuState) { this.cpu.PC = state.c.PC; this.cpu.SP = state.c.SP; }
  pause() { this.paused = true; }
  // like a real platform, resuming starts the emulation loop running
  // until the next breakpoint
  resume() { this.paused = false; this.advance(); }
  isRunning() { return !this.paused; }

  advance(novideo?: boolean): number {
    // execute instructions until breakpoint hit or budget exceeded
    var n = 0;
    while (!this.wasBreakpointHit() && n < 1000) {
      this.execInstruction();
      n++;
      this.debugClock++;
      this.evalDebugCondition();
    }
    return n;
  }

  execInstruction() {
    var op = this.readAddress(this.cpu.PC);
    switch (op) {
      case 0x20: {	// JSR abs
        var target = this.readAddress(this.cpu.PC + 1) | (this.readAddress(this.cpu.PC + 2) << 8);
        var ret = (this.cpu.PC + 2) & 0xffff;
        this.push((ret >> 8) & 0xff);
        this.push(ret & 0xff);
        this.cpu.PC = target;
        break;
      }
      case 0x60: {	// RTS
        var lo = this.pop();
        var hi = this.pop();
        this.cpu.PC = ((lo | (hi << 8)) + 1) & 0xffff;
        break;
      }
      default:	// NOP and anything else: treat as 1-byte instruction
        this.cpu.PC = (this.cpu.PC + 1) & 0xffff;
        break;
    }
  }

  push(b: number) {
    this.mem[0x100 + this.cpu.SP] = b & 0xff;
    this.cpu.SP = (this.cpu.SP - 1) & 0xff;
  }
  pop(): number {
    this.cpu.SP = (this.cpu.SP + 1) & 0xff;
    return this.mem[0x100 + this.cpu.SP];
  }
}

describe('BaseDebugPlatform stepOver', function () {

  function makePlatform(): TestStepPlatform {
    var p = new TestStepPlatform();
    // JSR $0005 ; NOP ; BRK
    p.mem.set([0x20, 0x05, 0x00, 0xEA, 0x00], 0x0000);
    // subroutine at $0005: LDA #$01 ; RTS
    p.mem.set([0xA9, 0x01, 0x60], 0x0005);
    p.cpu.PC = 0x0000;
    return p;
  }

  it('should step over a JSR to the following instruction', function () {
    var p = makePlatform();
    var sp0 = p.getSP();
    p.stepOver();	// runs the runEval loop via advance()
    assert.strictEqual(p.getPC(), 0x0003);	// not inside the subroutine
    assert.strictEqual(p.getSP(), sp0);		// subroutine returned
  });

  it('should single-step when instruction is not a call', function () {
    var p = makePlatform();
    p.cpu.PC = 0x0003;	// NOP
    p.stepOver();
    assert.strictEqual(p.getPC(), 0x0004);
  });

  it('should detect iscall on JSR opcode', function () {
    var p = makePlatform();
    var d = p.disassemble(0x0000, (a) => p.readAddress(a));
    assert.strictEqual(d.iscall, true);
    assert.strictEqual(d.nbytes, 3);
  });

});