I now have console running.
The corect firware should be DH_VTHX421L_*** for this devices.
However all I get on Serial console is:
HELLO! BOOT0 is starting! Nov 16 2018 02:18:28
boot0 version : 4.0.0
boot0 commit : 8
DRAM DRIVE INFO: V0.7
DRAM Type = 3 (2:DDR2,3:DDR3,6:LPDDR2,7:LPDDR3)
DRAM...