Since some time i am trying to translate the example EFM8UB2_HID_Keyboard in Simplicity to assembler 

most likely a losing proposition

what about SDCC?

This is strange, I tried the EFM8LB1_Flash example on EFM8LB STK and it works if I reserve the space.

did it with a 36x no problems

if you have an xdata write in an ISR, or - against my advice - use the LARGE model, you must disable interrupts during flash writes

This is strange, I tried the EFM8LB1_Flash example on EFM8LB STK and it works if I reserve the space.

did it with a 36x no problems

LCD works fine at baud rate 9600, 19200 etc 

I'm confused,

you state that the LCD is driven via SMB

what does that have to do with baud rates

driving it via SMB why 4 bit mode?

CODE (0x04FF-0xFBFF)

you NEED to have the assigned codespace include the vectors

OK, I changed the reserved flash to following

CODE (0x04FF-0xFBFF)

I used flash_write_addr=0x100; and program misbehaved after write process

flash_write_addr=0x400; the LCD displayed garbage instead of sensor values

CODE (0-0x1000, 0x2000-0xFFBF

CODE(0x01FF-0xFBFF)

IIRC that specifies where instructions go.  What about the interrupt vectors  they are 0x03  ...?

did the linker not complain, it should