main.hex firmware with an inversion of RESET pin:
https://drive.google.com/file/d/1QiRvCN29H0l-Kq0eJhdKs3WfHdrvEXrB/view?usp=sharing
source code:
https://drive.google.com/file/d/1-idzOalAeA77U9Ony_UZ1YfTT4d_M8j3/view?usp=sharing
avrdude.conf
https://drive.google.com/file/d/1bEraBArDpIUMMW7dt0KzH7qNNhkQd99W/view?usp=sharing
TARGET=atmega8
HFUSE=0xd9
LFUSE=0x9f
You can just flash the MCU without fuses
env for PlatformIO
[env:AT89S51]
platform = intel_mcs51
board = AT89S51
upload_protocol = custom
upload_command = sudo avrdude -c usbasp -p at89s51 -U flash:w:$SOURCE:i -C +./avrdude.conf