>
> This could mean that the com port read routine is getting garbage from
> the serial port, which the bootloader assumes comes from you pressing
> a key to stop the boot.

you are RIGHT!!!

i now remember a bit of garbage after connecting to terminal when
bootloader already started.

>
> It could be that your hardware returns junk characters when a byte is read
> with nothing hooked up.  You should build a biosboot_com0 with the
> '-DDIRECT_SERIAL' option disabled and see if that helps.
will try and report

is it possible that unplugged cable "receives" noise?

will just connecting extra resistor between ground and receive fix it?

any idea what resisitor? 22KOhm?