I noticed in the ODrive documentation that one of the GpioMode settings allows us to enable SPI_A on a GPIO port (GPIOMode setting 0x9). What can this SPI communication be used for? Can this be used for native/ascii communication with an external device, or is this exclusively for SPI communication with an encoder?
This is exclusively for encoder communication. You can communicate with an external device using USB, UART or CAN, but not SPI.