RV32I fields

opcode, rd/rs, funct3/7, and the I/S/B/U/J immediates.

A 32-bit RV32I instruction is a packed struct of opcode + register + immediate slices. ABI names (x0/zero, x1/ra, …) live in a package.

flowchart LR
  inst[inst_31_0] --> op[opcode]
  inst --> rd[rd]
  inst --> f3[funct3]
  inst --> rs[rs1_rs2]
  inst --> imm[imm]

wire [6:0] opcode = inst[6:0];
wire [4:0] rd     = inst[11:7];
wire [2:0] funct3 = inst[14:12];

I/S/B/U/J immediates are not a single contiguous field — sign-extend the slices the ISA names.

Wrong vs right

Wrong — treat inst[31:20] as the B-type immediate.

Right — decode by opcode, then assemble the immediate the spec draws.