Try with the interrupt on the clock pin. With SPI_CLOCK_DIV16 you have one microsecond to get thru your loop and be ready to process the next bit, not sure if that is doable.
Try with the interrupt on the clock pin. With SPI_CLOCK_DIV16 you have one microsecond to get thru your loop and be ready to process the next bit, not sure if that is doable.