In guide doc for BDT (which is found in archive with BTD utility) there are 2 ways to connect and flash TLSR devices. One is with USB (If target SoC has a HW USB), the second is using SWS interface.
I want to utilize USB way but it doesn't work. When i plug a tlsr8258 dongle with it's native FW into USB port of TELINK debugger i can at least read flash content of it using Memory Access tab in BDT. But i can't do this when i flash some custom FW into dongle. 
So is a USB programming not possible for clean tlsr825x crystals in their factory state? Do we need to attach a special USB bootloader capable FW snippet into main FW to make this feature work? I guess it's not possible at all flashing tlsr825x SoCs via USB on PC directly without Telink's debugger USB tool?