Ghidra 9.1.2: Unknown prototype attribute: type

[lab313ru]

Decompiler: Unable to initialize the DecompilerInterface: Could not register program: Low-level Error: Unknown prototype attribute: type

[n1tesh4dez]

I removed the type="unknown" attribute in the <prototype> tag of the data/languages/65816.cspec file and it worked for me. I use Ghidra 11.0.1 but guess this will work for you too. Btw this attribute is also not existing in the already in Ghidra included 6502.cspec file for the NES processor so it might just be not necessary at all.