DOKK / manpages / debian 10 / avr-libc / todo.3avr.en
todo(3avr) avr-libc todo(3avr)

todoTodo List
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From email with Marek: On smaller devices (all except ATmega64/128), __SPM_REG is in the I/O space, accessible with the shorter 'in' and 'out' instructions - since the boot loader has a limited size, this could be an important optimization.
Sat Feb 16 2019 Version 2.0.0