Qualcomm EDL mode

The Qualcomm Emergency Download mode, commonly known as Qualcomm EDL mode and officially known as Qualcomm HS-USB QD-Loader 9008[1] is a feature implemented in the boot ROM of a system on a chip by Qualcomm which can be used to recover bricked smartphones.[2][3] On Google's Pixel 3, the feature was accidentally shown to users after the phone was bricked.[4]

Image of a device with Qualcomm hardware booted in the Emergency Download Mode, represented in a Windows 10 machine.

Device support
See also: Devices using Qualcomm Snapdragon processors

For a device to support EDL it must be using Qualcomm hardware. The most widespread SoC from Qualcomm is the Snapdragon.

Access

ADB

The Android Debug Bridge can be utilized to get access to EDL mode, with the command adb reboot edl.[2]

Windows

The Qualcomm Product Support Tool (QPST) is normally used internally by service center executives for low-level firmware flashing to revive Android devices from a hard-brick or to fix persistent software issues. To flash the firmware, the tool communicates with supported devices via EDL.[5] The QPST has not been officially released by Qualcomm.

Linux

Qualcomm Download (QDL) is a tool to communicate with Qualcomm System On a Chip bootroms to install or execute code. The source code is maintained by Bjorn Andersson aka andersson.[6]

Test points

Qualcomm implemented motherboards always include a test point. These can vary from phone models. Generally, test points can be a pair of contacts, and in some devices can be separated. EDL can be accessed by opening the back of the phone, finding sources of the test points that depends on the model, and by using a pair of metal tweezers, which works in most Qualcomm based devices, to short the connectors, and boot the phone into EDL that can be later taken actions with the use of the necessary tools.

EDL Deep Flash Cable
General appearance of a EDL Deep Flash Cable that can be found online. The cable is able to put the phone into a deep flash state, possible to boot it into EDL in any case.

Qualcomm implemented motherboards, with the presence of EDL, can be booted to EDL via the use of a EDL Deep Flash Cable. This specific cable has a general appearance of a button present in the cable. The button can be represented as a switch, to be able to make the phone boot into EDL mode. With the use of the cable, in most devices and cases, it will not be necessary to use the test points. The cable also works on hard-bricked devices to boot them into EDL mode.

References
  1. Zhao, Longze; Xi, Bin; Wu, Shunxiang; Aizezi, Yasen; Ming, Daodong; Wang, Fulin; Yi, Chao (2018). "Physical Mirror Extraction on Qualcomm-based Android Mobile Devices". Proceedings of the 2nd International Conference on Computer Science and Application Engineering. Hohhot, China: ACM Press. pp. 1–5. doi:10.1145/3207677.3278046. ISBN 978-1-4503-6512-3. S2CID 53038902.
  2. EASTTOM, CHUCK (2021). An In-Depth Guide to Mobile Device Forensics. [S.l.]: CRC Press. p. 72. ISBN 978-0-367-63300-4. OCLC 1250310301.
  3. Tang, Qinghao (2021). Internet of things security : principles and practice. Fan Du. Singapore. p. 166. ISBN 978-981-15-9942-2. OCLC 1236261208.{{cite book}}: CS1 maint: location missing publisher (link)
  4. Amadeo, Ron (2021-09-03). "Reports of Pixel 3s bricking with "EDL" message are growing". Ars Technica. Retrieved 2021-09-11.
  5. Bhardwaj, Dhananjay (April 2, 2021). "Download QPST Flash Tool & How to Use it to Flash Firmware on Qualcomm Android Devices". The Custom Droid. Retrieved February 21, 2022.
  6. Andersson, Bjorn. "Source code of qdl". Github. Retrieved February 21, 2022.
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