Ok, i managed to proceed a little bit further with lots of googling
I found the pinout of the opensprinkler isp port and connected my usbasp to it. The atmega664 was detected. With avr dude, i sent the command to use the external oscillator and then flashed the hex file of the current firmware.
Avr dude reported a successful flash. U unfortunately i cant test i yet, there must be a Hardware issue, my Display doesnt power on.
But there is one more Problem: i dont know how to flash the bootloader and i would like to have it so that i can use the usb port for further firmware changes. The ch334g driver is installed under windows and the device is recognizdd, but without the bootloader there is no chance to use the upgrade tool.
I got the optiboot hex for the 664 but i dont known how to flash it..
Can spmebody please tell me the avrdude synthax for fladhig the bootloader?