You have the original ASM disassembled, ROM, kernal and comments at https://www.pagetable.com/c64ref/c64disasm/
You have the original ASM disassembled, ROM, kernal and comments at https://www.pagetable.com/c64ref/c64disasm/
I've used pagetable.com quite a lot for reference to see how things were done in CBM BASIC. I didn't always follow that direction (also looked at GW-BASIC, and others), but it has proven very useful to either set me on a well-trod direction or to validate ideas I'd already had.
Or, although not what you asked: https://github.com/microsoft/GW-BASIC
My references (35 years) ago were some books published by Data Becker GmbH.
Note also that there were basic extensions to address the limitations of CBM basic like the Simon basic cartridge.
That Simon basic was a wonder in their own. Written by a gifted teenager and extending by mapping addresses in the ROM. It was possible to write sprites and graph in basic without pokes (no ASM needed).
Edit: I missed the comment downthread that says that some of that code was released a couple of years ago.