custom Atmega2560 bootloader

Hi.
I whant to make some chahnges in functionality of standart arduino Mega2560 bootloader.
I decide to modify stk500V2 bootloader
First of all, I whant to compile this bootloader using Atmel studio. If this bootloader become work then I start to modify it.

This task looks easy.

  1. I create new project for Atmega2560 mcu

  2. import source files (C:\Users\myuser\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.6.15\bootloaders\stk500v2) Setup memory - add option .text=0x7000 in FLUSH segment (project propertie/toolcain/AVR/GNU linker/memory settings)

  3. make some defines
    #define F_CPU 16000000UL
    #define MEGA_BOARD
    #define BLINK_LED_WHILE_WAITING

  4. Build project.

IMPORTANT:
I don't make any changes is source code. All voids, and function is original!!! I Just add 3 defines (from step #4). Thet are present in original Makefile. I dont use original Makefile becouse i whant to build bootloader in Atmel studio.

After thet I burn bootloader to Mega board using my arduino UNO boar as programmer (Examples/ArduinoISP)

My Mega board looks like alive. After powerup -> led become blink (as it is programmed is bootloader)
When I open Serial monitor and send !!! command => bootloader answer to me....

!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!
Arduino explorer stk500V2 by MLS
Bootloader>

BUT When I try to upload Blink scatch to My Mega board - Arduino IDE report error

avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer
Произошла ошибка при загрузке скетча

When i burn original bootloader (C:\Users\myuser\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.6.15\bootloaders\stk500v2\stk500boot_v2_mega2560.hex) - sketch uploads without any problem.

Is there any people who make working mod of thes bootloader? or any other bootloader? Can you help me to understand what the problem is?