title: How to add a new custom instruction in the RISCV instruction set
body: <p>From many days I've been trying to simulate new custom instructions using the RISV ISA simulator but haven't been successful in creating a new instruction and compiling it with the riscv assembler. I tried adding my own new opcode in risk-tools/riscv-opcodes/opcodes. I tried creating a custom opcode to do the function of ADD then replaced ADD with my custom instruction in the assembly code but the assembler failed to compile it saying instruction not found. Also when I'm trying to use the built in custom instructions custom0,1,2 I'm always getting the error of invalid operands.</p>