nes-emu/ppu/registers/PPUStatus.spec.js

A NES emulator

"use strict";

var _createTestContext = _interopRequireDefault(require("../../helpers/createTestContext"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
const should = require("chai").Should();
const ADDRESS = 0x2002;
describe("CPU/PPU registers interaction", () => {
  describe("PPUStatus", () => {
    let ppu, memory, register;
    beforeEach(() => {
      ({
        ppu,
        memory
      } = (0, _createTestContext.default)());
      register = ppu.registers.ppuStatus;
    });
    it("is read-only", () => {
      register.setValue(123);
      memory.readAt(ADDRESS).should.equal(123);
      memory.writeAt(ADDRESS, 456);
      memory.readAt(ADDRESS).should.equal(123);
    });
    it("can read the register", () => {
      memory.readAt(ADDRESS).should.equal(0b10000000);
      register.spriteOverflow = 1;
      register.sprite0Hit = 1;
      memory.readAt(ADDRESS).should.equal(0b01100000);
    });
    describe("side effects", () => {
      it("resets the vertical blank flag on every read", () => {
        register.isInVBlankInterval = 1;
        memory.readAt(ADDRESS);
        register.isInVBlankInterval.should.equal(0);
      });
      it("resets PPUAddr's latch on every read", () => {
        ppu.loopy.latch = true;
        memory.readAt(ADDRESS);
        ppu.registers.ppuAddr.latch.should.equal(false);
      });
    });
  });
});