Usbtiny has a protocol or firmware problem that prevents it from reading
flash above 64 kB in page mode (used by -U flash:r:... and -U flash✌️...).
This commit fixes that problem by falling back on byte access for flash paged
reads above 64k. It also issues the correct load extended address command for
parts with more than 128 kB flash thus extending support to ATmega2560 et al.
It is limited to exactly sending (and receiving) multiples of 4 bytes,
and unlike programming mode where slave select isn't required, SS must
be held low for SPI to work. USBtiny programmers don't usually have
a wire for SS.
Stefan Rueger
David Fries
Jörg Wunsch
Marius Greuel
Yegor Yefremov