peices of code for my light engines
master spi arduino mega at 8mhz sending 10 bytes, 10th byte can be crc8 byte. tested to 21mhz arduino due as slave spi dma 10byte transfer, could be more if code changed.
uart0 and uart1 spi on the due for graphics test, needs dma for the due. can use on the mega2560 if you can use the non normal broke out sck1 pin.