Short answer

esptool fails to enter download mode. Where do I look?

  • GPIO0 must be held low at reset for download. A floating strap or a product button that never reaches GPIO0 will miss the window.
  • USB-UART drivers, the wrong COM port, and a cable that only charges are common. Try another cable before rewriting the flash command.
  • Auto-reset circuits need EN and GPIO0 timed correctly. Custom boards without the classic DTR/RTS network need a manual BOOT button.
  • If the chip enumerates but flash times out, check 3.3 V under load and crystal start. Power first, then the tool flags.

中文

短答

esptool 进不了下载模式，看哪？

  • 复位时 GPIO0 要拉低才能进下载。悬空、或产品按键根本没接到 GPIO0，都会错过窗口。
  • 驱动、COM 口号、只充电不传数据的线都很常见。先换线，再改 flash 命令参数。
  • 自动复位要 EN 与 GPIO0 时序正确。没有经典 DTR/RTS 网络的板子，需要手动 BOOT。
  • 能枚举但烧录超时，先查负载下的 3.3 V 和晶振起振。先电源，再工具参数。