I am currently implementing an autonomous quadcopter with stereo vision using raspberry Pi. One (Let's call this Pi_1) is responsible for stereo vision the other is responsible for motor control and trajectory planning (Pi_2). I was looking for a way to transfer a 480 element float vector via GPIO from Pi_1 to Pi_2. Pi_1 stereovision program runs at 2Hz while Pi_2 motor control runs at 210Hz.
Is there any protocol fast enough to deliver this amount of information to the second raspberry pi via GPIO?
I am currently looking at SPI but I saw that the Raspberry Pi cannot be turned to a Slave making it not an option. I also looked at UART however it is too slow for my needs. All the I2c ports on the Pi are currently being used by the stereo vision cameras and the IMU's. If the gpio option is not feasible, I am also open for other suggestions such as using other hardware (middle man) or wireless options.