chisel/Buraq-mini/RV32i/src/main/scala/core/ImmediateGeneration.scala

package core

import chisel3._
import chisel3.util.Cat
import chisel3.util.Fill

class ImmediateGeneration extends Module {
    val io = IO(new Bundle {
        val instruction = Input(UInt(32.W))
        val pc = Input(SInt(32.W))
        val s_imm = Output(SInt(32.W))
        val sb_imm = Output(SInt(32.W))
        val u_imm = Output(SInt(32.W))
        val uj_imm = Output(SInt(32.W))
        val i_imm = Output(SInt(32.W))
    })
    // ----- Calculating S-Immediate ------ //

    val s_lower_half = io.instruction(11,7)     // bits 7-11 from 32 bits
    val s_upper_half = io.instruction(31,25)    // bits 25-31 from 32 bits
    var s_imm_12 = Cat(s_upper_half, s_lower_half)    // merging immediates together to form 12 bits
    val s_imm_32 = Cat(Fill(20, s_imm_12(11)), s_imm_12)   // sign extending 12 bits to 32 bits and merging the 12 bit immediate 
    io.s_imm := s_imm_32.asSInt


    // ----- Calculating SB-Immediate ------ //

    val sb_lower_half = io.instruction(11,8)
    val sb_upper_half = io.instruction(30, 25)
    val sb_11thbit = io.instruction(7)
    val sb_12thbit = io.instruction(31)
    val sb_imm_13 = Cat(sb_12thbit, sb_11thbit, sb_upper_half, sb_lower_half, 0.S)
    val sb_imm_32 = Cat(Fill(19, sb_imm_13(12)), sb_imm_13).asSInt
    io.sb_imm := sb_imm_32 + io.pc


    // ----- Calculating U-Immediate ------ //

    val u_imm_20 = io.instruction(31,12)
    var u_imm_32 = Cat(Fill(12, u_imm_20(19)), u_imm_20)
    // val shift_const = 12.S
    val u_imm_32_shifted = u_imm_32 << 12.U
    io.u_imm := u_imm_32_shifted.asSInt


    // ----- Calculating UJ-Immediate ----- //
    
    val uj_lower_half = io.instruction(30, 21)
    val uj_11thbit = io.instruction(20)
    val uj_upper_half = io.instruction(19, 12)
    val uj_20thbit = io.instruction(31)
    val uj_imm_21 = Cat(uj_20thbit, uj_upper_half, uj_11thbit, uj_lower_half, 0.S)
    val uj_imm_32 = Cat(Fill(11, uj_imm_21(20)), uj_imm_21).asSInt
    io.uj_imm := uj_imm_32 + io.pc


    // ----- Calculating I-Immediate ----- //

    val i_imm_12 = io.instruction(31, 20)
    val i_imm_32 = Cat(Fill(20, i_imm_12(11)), i_imm_12)
    io.i_imm := i_imm_32.asSInt
}