[Android General] JuhaniJ:
When I plug in the Doogee X20L via a USB cable to the PC, the USB VID:PID changes many times: 0e8d:2000 -> 0e8d:0003 -> 0e8d:2000 -> 0e8d:20ff. When plugging the cable in I do not hold any buttons on the phone. When I compare phones for which the Readback works, the USB VID:PID remains 0e8d:2000.

The VID:PID 0e8d:2000 means vendor Mediatek and product MT65xx Preloader.

Here is what SP Flash Tool outputs to the console when plugging in the X20L during Readback:

[root@hp SP_Flash_Tool_v5.1728_Linux]# ./flash_tool
QMetaObject::connectSlotsByName: No matching signal for on_pushButton_browser_clicked()
QThread::setPriority: Cannot set priority, thread is not running
"07-25-2019"
QObject::moveToThread: Cannot move objects with a parent
Connecting to BROM...
Scanning USB port...
Search usb, timeout set as 3600000 ms
add@/devices/pci0000:00/0000:00:13.5/usb1/1-7

add@/devices/pci0000:00/0000:00:13.5/usb1/1-7/1-7:1.0

add@/devices/pci0000:00/0000:00:13.5/usb1/1-7/1-7:1.1

bind@/devices/pci0000:00/0000:00:13.5/usb1/1-7

add@/module/cdc_acm

bind@/devices/pci0000:00/0000:00:13.5/usb1/1-7/1-7:1.0

add@/devices/pci0000:00/0000:00:13.5/usb1/1-7/1-7:1.1/tty/ttyACM0

vid is 0e8d

device vid = 0e8d

pid is 2000

device pid = 2000

com portName is: /dev/ttyACM0

Total wait time = -1566756657.000000
USB port is obtained. path name(/dev/ttyACM0), port name(/dev/ttyACM0)
USB port detected: /dev/ttyACM0
BROM connected
Downloading & Connecting to DA...
connect DA end stage: 2, enable DRAM in 1st DA: 0
COM port is open. Trying to sync with the target...
Failed to Connect DA: S_BROM_DOWNLOAD_DA_FAIL
Disconnect!
BROM Exception! ( ERROR : S_BROM_DOWNLOAD_DA_FAIL (2004)

[H/W] Fail to download DA to baseband chip's internal SRAM!
[HINT]:
1. There's an cable communication problem between FlashTool and BootROM.
2. Target might be shutdown unexpectedly or target lost power supply.
[ACTION]
1. Try again.
2. Proceed H/W checking in download cable and target side com port.
3. Monitor if power-drop occured in target side.)((ConnectDA,../../../flashtool/Conn/Connection.cpp,131))

And here is dmesg for X20L:

[2019-08-25 21:10:57] usb 1-7: new high-speed USB device number 5 using ehci-pci
[2019-08-25 21:10:57] usb 1-7: New USB device found, idVendor=0e8d, idProduct=2000, bcdDevice= 1.00
[2019-08-25 21:10:57] usb 1-7: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[2019-08-25 21:10:57] usb 1-7: Product: MT65xx Preloader
[2019-08-25 21:10:57] usb 1-7: Manufacturer: MediaTek
[2019-08-25 21:10:58] cdc_acm 1-7:1.0: Zero length descriptor references
[2019-08-25 21:10:58] cdc_acm: probe of 1-7:1.0 failed with error -22
[2019-08-25 21:10:58] cdc_acm 1-7:1.1: ttyACM0: USB ACM device
[2019-08-25 21:10:58] usbcore: registered new interface driver cdc_acm
[2019-08-25 21:10:58] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters
[2019-08-25 21:10:58] usb 1-7: USB disconnect, device number 5
[2019-08-25 21:10:59] usb 5-1: new full-speed USB device number 2 using ohci-pci
[2019-08-25 21:10:59] usb 5-1: New USB device found, idVendor=0e8d, idProduct=0003, bcdDevice= 1.00
[2019-08-25 21:10:59] usb 5-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[2019-08-25 21:10:59] cdc_acm 5-1:1.0: ttyACM0: USB ACM device
[2019-08-25 21:10:59] usbcore: registered new interface driver option
[2019-08-25 21:10:59] usbserial: USB Serial support registered for GSM modem (1-port)
[2019-08-25 21:11:03] usb 5-1: USB disconnect, device number 2
[2019-08-25 21:11:04] usb 1-7: new high-speed USB device number 7 using ehci-pci
[2019-08-25 21:11:05] usb 1-7: New USB device found, idVendor=0e8d, idProduct=2000, bcdDevice= 1.00
[2019-08-25 21:11:05] usb 1-7: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[2019-08-25 21:11:05] usb 1-7: Product: MT65xx Preloader
[2019-08-25 21:11:05] usb 1-7: Manufacturer: MediaTek
[2019-08-25 21:11:05] cdc_acm 1-7:1.0: Zero length descriptor references
[2019-08-25 21:11:05] cdc_acm: probe of 1-7:1.0 failed with error -22
[2019-08-25 21:11:05] cdc_acm 1-7:1.1: ttyACM0: USB ACM device
[2019-08-25 21:11:06] usb 1-7: USB disconnect, device number 7
[2019-08-25 21:11:07] usb 1-7: new high-speed USB device number 8 using ehci-pci
[2019-08-25 21:11:07] usb 1-7: device not accepting address 8, error -71
[2019-08-25 21:11:15] usb 5-1: new full-speed USB device number 3 using ohci-pci
[2019-08-25 21:11:16] usb 5-1: not running at top speed; connect to a high speed hub
[2019-08-25 21:11:16] usb 5-1: New USB device found, idVendor=0e8d, idProduct=20ff, bcdDevice=ff.ff
[2019-08-25 21:11:16] usb 5-1: New USB device strings: Mfr=3, Product=4, SerialNumber=5
[2019-08-25 21:11:16] usb 5-1: Product: Android
[2019-08-25 21:11:16] usb 5-1: Manufacturer: Android
[2019-08-25 21:11:16] usb 5-1: SerialNumber: 0123456789ABCDEF
[2019-08-25 21:11:16] hid-generic 0003:0E8D:20FF.0003: No inputs registered, leaving
[2019-08-25 21:11:16] hid-generic 0003:0E8D:20FF.0003: hidraw2: USB HID v1.01 Device [Android Android] on usb-0000:00:13.3-1/input0

And here is dmesg for Soyes XS for which the Readback succeeds:

[2019-08-20 10:21:03] usb 1-1.2: new high-speed USB device number 30 using ehci-pci
[2019-08-20 10:21:03] usb 1-1.2: New USB device found, idVendor=0e8d, idProduct=2000, bcdDevice= 1.00
[2019-08-20 10:21:03] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[2019-08-20 10:21:03] usb 1-1.2: Product: MT65xx Preloader
[2019-08-20 10:21:03] usb 1-1.2: Manufacturer: MediaTek
[2019-08-20 10:21:03] cdc_acm 1-1.2:1.0: Zero length descriptor references
[2019-08-20 10:21:03] cdc_acm: probe of 1-1.2:1.0 failed with error -22
[2019-08-20 10:21:03] cdc_acm 1-1.2:1.1: ttyACM0: USB ACM device

Why the VID:PID does not remain 0e8d:2000 for Doogee X20L?