nes-emu/ppu/registers/OAMDMA.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _registers = require("../../registers");
var _constants = _interopRequireDefault(require("../../constants"));
var _helpers = require("../../helpers");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * OAM DMA Register (> write)
 *
 * Writing XX here will upload 256 bytes of data from CPU page $XX00-$XXFF to the internal PPU OAM.
 * This process takes 513 CPU cycles (+1 if on an odd cycle). The CPU is suspended during the operation.
 */
class OAMDMA extends _registers.WriteOnlyInMemoryRegister {
  /** Writes 256 bytes from page $`byte` to PPU's internal OAM. */
  writeAt(__, byte) {
    const {
      cpu,
      ppu
    } = this.context;
    for (let i = 0; i < 256; i++) {
      const address = _helpers.Byte.to16Bit(byte, i);
      const value = cpu.memory.readAt(address);
      ppu.oamRam[i] = value;
    }
    cpu.extraCycles += _constants.default.OAMDMA_CPU_CYCLES + (cpu.cycle % 2 === 1);
  }
}
exports.default = OAMDMA;