I was analyzing example projects from Atmel Studio for SAM D20 parts. There are many files inside ASF subfolders, but they are all .c and .h (there's just the linker script).
Where are the assembler instructions that are executed immediately after startup? Is the startup function entirely written in C?
I was reading the tutorial from Miro Samek at this link: he writes the code is generic for any ARM-based MCU, but there are a lot of assembly code.
I think that tutorial is for older ARM architectures that aren't compatible with new Cortex-M architectures, but I'm not sure.