nes-emu/cpu/instructions/branching.spec.js

A NES emulator

"use strict";

var _2 = _interopRequireDefault(require("."));
var _createTestContext = _interopRequireDefault(require("../../helpers/createTestContext"));
var _lodash = _interopRequireDefault(require("lodash"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
const should = require("chai").Should();
describe("instructions", () => {
  describe("branching", () => {
    let cpu, context;
    beforeEach(() => {
      ({
        cpu,
        context
      } = (0, _createTestContext.default)());
      cpu.pc.value = 0x1000;
    });
    [{
      instruction: "BCC",
      flag: "c"
    }, {
      instruction: "BNE",
      flag: "z"
    }, {
      instruction: "BPL",
      flag: "n"
    }, {
      instruction: "BVC",
      flag: "v"
    }].forEach(_ref => {
      let {
        instruction,
        flag
      } = _ref;
      describe(instruction, () => {
        it("jumps if the flag is clear", () => {
          cpu.flags[flag] = false;
          _2.default[instruction].execute(context, 0x2000);
          cpu.pc.value.should.equal(0x2000);
          cpu.extraCycles.should.equal(1);
        });
        it("doesnt jump if the flag is set", () => {
          cpu.extraCycles = 3;
          cpu.flags[flag] = true;
          _2.default[instruction].execute(context, 0x2000);
          cpu.pc.value.should.equal(0x1000);
          cpu.extraCycles.should.equal(0);
        });
      });
    });
    [{
      instruction: "BCS",
      flag: "c"
    }, {
      instruction: "BEQ",
      flag: "z"
    }, {
      instruction: "BMI",
      flag: "n"
    }, {
      instruction: "BVS",
      flag: "v"
    }].forEach(_ref2 => {
      let {
        instruction,
        flag
      } = _ref2;
      describe(instruction, () => {
        it("jumps if the flag is set", () => {
          cpu.flags[flag] = true;
          _2.default[instruction].execute(context, 0x2000);
          cpu.pc.value.should.equal(0x2000);
          cpu.extraCycles.should.equal(1);
        });
        it("doesnt jump if the flag is clear", () => {
          cpu.extraCycles = 3;
          cpu.flags[flag] = false;
          _2.default[instruction].execute(context, 0x2000);
          cpu.pc.value.should.equal(0x1000);
          cpu.extraCycles.should.equal(0);
        });
      });
    });
    describe("JMP", () => {
      it("jumps to the address", () => {
        _2.default.JMP.execute(context, 0x1234);
        cpu.pc.value.should.equal(0x1234);
      });
    });
    describe("JSR", () => {
      it("pushes the current program counter (minus one) to the stack and jumps to the address", () => {
        cpu.pc.value = 0xfe31;
        _2.default.JSR.execute(context, 0x1234);
        cpu.stack.pop2Bytes().should.equal(0xfe30);
        cpu.pc.value.should.equal(0x1234);
      });
    });
    describe("RTI", () => {
      it("pulls the processor flags and the program counter from the stack", () => {
        cpu.stack.push2Bytes(0xfe35);
        cpu.stack.push(0b10101000);
        _2.default.RTI.execute(context);
        cpu.flags.toByte().should.equal(0b10101000);
        cpu.pc.value.should.equal(0xfe35);
      });
    });
    describe("RTS", () => {
      it("pulls the program counter (plus one) from the stack", () => {
        cpu.stack.push2Bytes(0xfe35);
        _2.default.RTS.execute(context);
        cpu.pc.value.should.equal(0xfe36);
      });
    });
  });
});