If someone stumbles upon this thread. Here is a link to someone's thread that made circuit board schematics for the DS and DS Lite
https://bitbuilt.net/forums/index.php?threads/ds-fat-ds-lite-dsi-pcb-scan-and-schematic.6184/
I can only say that...
You could also just use Godmode9. Go to the NCCH image options and select Extract .code. This should extract and decompress the code.bin and put it into the gm9 folder on the SD card
Video is actually still online but only accessable over IPv6
Uploaded it somewhere else hopefully accessable for you
https://c.web.de/@322276937898656556/5gJNiuxzQNyizalkJNMUiw