I am upgrading a mega88 board to rcv some rather slow spi data (rcv as a slave, nothing needs sent). The data has this protocol, from another device sending a rotating shaft RPM & can't be changed: cs goes low, RPM lsb sent, 16 bits total, RPM msb last, clocked on rising edge, after 16 clocks, cs goes high.
Since it is slowly incoming from a slow clocking, I don't want to poll between bytes & yet need to stay synchronized with the CS falling edge (so the bytes don't get accidentally swapped). There might be times where the reading can't occur, due to other things being busy (missing a read is allowable).
I thought about using SPI interrupts, which would eliminate a lot of excess polling, but not sure if there is a simple way to keep track of which byte is which.