Qualcomm — Flash Loader V1.0 [best]

: Operates by communicating with the device in Qualcomm HS-USB QDLoader 9008 mode (EDL), which allows for low-level flashing even if the phone's operating system or bootloader is corrupted.

If a user flashes the wrong bootloader or corrupts the "aboot" (Android Bootloader) partition, the device may no longer enter fastboot. The Flash Loader via EDL is the only recovery method. Qualcomm Flash Loader V1.0