Did you know you can configure them to be addresses that feed a built-in MUX allowing you to manage up to 15 or 16 total SPI devices
I'd like to find a way to use the CS lead that actually isn't connected to any of the Arduino pins
Timer 1 channel 0 must be used with SPI somehow because when I use that timer to manage another function it completely disables SPI.
Yes, either internally MUXd for 4 devices or externally MUXd for 15 devices.
QuoteI'd like to find a way to use the CS lead that actually isn't connected to any of the Arduino pinsUmmm, using telepathy?
There should be no relationship between the two, I suspect a bug in either your code or the libraries.
#define BOARD_SPI_DEFAULT_SS BOARD_SPI_SS2
#define BOARD_SPI_DEFAULT_SS BOARD_SPI_SS3
On the Due schematic, SS3 is pin 142, PB23, but is not connected to anything.