https://github.com/cs107e/cs107e.github.io
http://wiki.osdev.org/Calling_Conventions
http://wiki.osdev.org/Linker_Scripts
http://wiki.osdev.org/Printing_To_Screen
http://wiki.osdev.org/Exceptions#General_Protection_Fault
https://en.wikipedia.org/wiki/X86_calling_conventions
http://repo.or.cz/w/lightOS.git
https://littleosbook.github.io/
http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html

http://x86.renejeschke.de/html/file_module_x86_id_139.html
http://retired.beyondlogic.org/serial/serial1.htm
https://pdos.csail.mit.edu/6.828/2014/reference.html

tutorials:

https://littleosbook.github.io
http://www.henkessoft.de/OS_Dev/OS_Dev1.htm

In C#:
https://github.com/FlingOS/FlingOS

In Rust:
http://os.phil-opp.com/

Interrupts:
http://wiki.osdev.org/Exceptions
http://wiki.osdev.org/Interrupt_Descriptor_Table
http://beefchunk.com/documentation/hardware/microprocessors/intel/i80386/Chap9.html
http://www.cs.cmu.edu/~ralf/files.html
https://blog.packagecloud.io/eng/2016/04/05/the-definitive-guide-to-linux-system-calls/

A20:
http://www.independent-software.com/writing-your-own-toy-operating-system-enabling-the-a20-line/

longjmp:
http://blog.reverberate.org/2013/05/deep-wizardry-stack-unwinding.html
http://prettyos.de

PIC:
http://www.brokenthorn.com/Resources/OSDevPic.html