nes-emu/ppu/renderers/_3_vBlankLine.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = vBlankLine;
var _constants = _interopRequireDefault(require("../../constants"));
var _constants2 = require("../../cpu/constants");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/** Runs on scanline 241, which starts the VBlank period and can trigger NMIs. */
function vBlankLine(_ref) {
  let {
    ppu
  } = _ref;
  if (ppu.cycle === _constants.default.PPU_CYCLE_VBLANK - 1) {
    ppu.registers.ppuStatus.isInVBlankInterval = 1;
    // some games with tight loops (like Bomberman) need to "see" the VBlank flag before jumping to the NMI handler
    return _constants.default.BREAK_FLAG;
  }
  if (ppu.cycle === _constants.default.PPU_CYCLE_VBLANK) {
    ppu.registers.ppuStatus.isInVBlankInterval = 1;
    if (ppu.registers.ppuCtrl.generateNmiAtStartOfVBlank) return _constants2.interrupts.NMI;
  }
  return null;
}