So I resolderd yesterday the trim resistor to a 4.7k resistor. Now the 0.9V is at 0.86V and I get a hashrate of approx 2.3Gh/s with one chip.
This is more than before with two miners.
When I connect the slave miner the rashrate goes down I don't konw why. Has someone a clue?
Did you change some value in spidev.c file? this speed is the speed of the SPI (Serial Peripheral Interface) of the RPi, maybe need more speed of communications to manage two devices.
Regards