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lingbaoboy 原贴方法是不行的，下面回复有说。
For anyone else who might run into this issue in future, here's what I did to fix it:
- Get into Download mode. To do so, power off the device and hook it up to a power source. You'll then see the Android One boot screen followed by the charging icon. At the charging icon, press vol DN+power for 5s. Then you're in Download mode. You'll know when it says 'Download mode' on the Android One boot screen.
- Now that you're in Download mode, your device can be recognised by fastboot (but not adb). Send 'fastboot oem HALT'. Then disconnect the cable, which will cut power to the device. Plug your device into power again (AC) where it'll show the charging animation again. Press vol UP+power until you see the 'No command' screen. Once at this screen, hold power and push vol UP. You're then at the recovery screen.
- adb will now work. sideload O (213B '00WW' package) to the device and perform a data wipe (optional, but I did it anyway). Send the package to the device via adb sideload.
- Reboot the device once you're done sideloading O.