#Guides
https://emil.fi/avr A basic getting started / how-to guide focusing on the essential
https://emil.fi/toolchain How to set up the toolchain from scratch
http://polprog.net/blog/serial/ Serial communications
http://polprog.net/blog/asm/ Assembly things
http://msoe.us/taylor/tutorial/ce2810/candasm More assembly things
http://ruemohr.org/~ircjunk/avr/asmtut/asm_crash.html Even moar

#References
https://www.engbedded.com/fusecalc/ Hugely important when programming a chip from scratch
https://www.nongnu.org/avr-libc/ The best and most important reference for AVR programming, ever
https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html Interrupts
https://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html Storage in rom
https://www.nongnu.org/avr-libc/user-manual/mem_sections.html
https://www.nongnu.org/avr-libc/user-manual/inline_asm.html
http://tom-itx.no-ip.biz:81/~webpage/index.php
https://www.avrfreaks.net/sites/default/files/forum_attachments/XMega_Tutorial.pdf

#Examples
https://emil.fi/d/streamer.c interrupts, uart, timer, gpio
https://emil.fi/d/ping.c interrupts, uart, timers
https://emil.fi/d/taikasauva.c interrupts, ADC, filtering, timers
/code/ledthingy.c attiny85, interrupts, i2c, gpio, sleep