from nmigen import *

class rvfi_insn_srai(Elaboratable):
    def __init__(self, RISCV_FORMAL_ILEN=32, RISCV_FORMAL_XLEN=32):
        self.RISCV_FORMAL_ILEN = RISCV_FORMAL_ILEN
        self.RISCV_FORMAL_XLEN = RISCV_FORMAL_XLEN
        self.rvfi_valid = Signal(1)
        self.rvfi_insn = Signal(self.RISCV_FORMAL_ILEN)
        self.rvfi_pc_rdata = Signal(self.RISCV_FORMAL_XLEN)
        self.rvfi_rs1_rdata = Signal(self.RISCV_FORMAL_XLEN)
        self.rvfi_rs2_rdata = Signal(self.RISCV_FORMAL_XLEN)
        self.rvfi_mem_rdata = Signal(self.RISCV_FORMAL_XLEN)
        self.spec_valid = Signal(1)
        self.spec_trap = Signal(1)
        self.spec_rs1_addr = Signal(5)
        self.spec_rs2_addr = Signal(5)
        self.spec_rd_addr = Signal(5)
        self.spec_rd_wdata = Signal(self.RISCV_FORMAL_XLEN)
        self.spec_pc_wdata = Signal(self.RISCV_FORMAL_XLEN)
        self.spec_mem_addr = Signal(self.RISCV_FORMAL_XLEN)
        self.spec_mem_rmask = Signal(int(self.RISCV_FORMAL_XLEN // 8))
        self.spec_mem_wmask = Signal(int(self.RISCV_FORMAL_XLEN // 8))
        self.spec_mem_wdata = Signal(self.RISCV_FORMAL_XLEN)
    def ports(self):
        input_ports = [
            self.rvfi_valid,
            self.rvfi_insn,
            self.rvfi_pc_rdata,
            self.rvfi_rs1_rdata,
            self.rvfi_rs2_rdata,
            self.rvfi_mem_rdata
        ]
        output_ports = [
            self.spec_valid,
            self.spec_trap,
            self.spec_rs1_addr,
            self.spec_rs2_addr,
            self.spec_rd_addr,
            self.spec_rd_wdata,
            self.spec_pc_wdata,
            self.spec_mem_addr,
            self.spec_mem_rmask,
            self.spec_mem_wmask,
            self.spec_mem_wdata
        ]
        return input_ports + output_ports
    def elaborate(self, platform):
        m = Module()

        # I-type instruction format (shift variation)
        insn_padding = Signal(self.RISCV_FORMAL_ILEN)
        m.d.comb += insn_padding.eq(self.rvfi_insn >> 32)
        insn_funct6 = Signal(7)
        m.d.comb += insn_funct6.eq(self.rvfi_insn[26:32])
        insn_shamt = Signal(6)
        m.d.comb += insn_shamt.eq(self.rvfi_insn[20:26])
        insn_rs1 = Signal(5)
        m.d.comb += insn_rs1.eq(self.rvfi_insn[15:20])
        insn_funct3 = Signal(3)
        m.d.comb += insn_funct3.eq(self.rvfi_insn[12:15])
        insn_rd = Signal(5)
        m.d.comb += insn_rd.eq(self.rvfi_insn[7:12])
        insn_opcode = Signal(7)
        m.d.comb += insn_opcode.eq(self.rvfi_insn[:7])

        misa_ok = Signal(1)
        m.d.comb += misa_ok.eq(1)

        # SRAI instruction
        result = Signal(self.RISCV_FORMAL_XLEN)
        m.d.comb += result.eq((self.rvfi_rs1_rdata >> insn_shamt) | (-(self.rvfi_rs1_rdata < 0) << (self.RISCV_FORMAL_XLEN - insn_shamt))) # https://stackoverflow.com/a/25207042
        m.d.comb += self.spec_valid.eq(self.rvfi_valid & (~insn_padding) & (insn_funct6 == 0b010000) & (insn_funct3 == 0b101) & (insn_opcode == 0b0010011) & ((~insn_shamt[5]) | (self.RISCV_FORMAL_XLEN == 64)))
        m.d.comb += self.spec_rs1_addr.eq(insn_rs1)
        m.d.comb += self.spec_rd_addr.eq(insn_rd)
        m.d.comb += self.spec_rd_wdata.eq(Mux(self.spec_rd_addr, result, 0))
        m.d.comb += self.spec_pc_wdata.eq(self.rvfi_pc_rdata + 4)

        # default assignments
        m.d.comb += self.spec_rs2_addr.eq(0)
        m.d.comb += self.spec_trap.eq(~misa_ok)
        m.d.comb += self.spec_mem_addr.eq(0)
        m.d.comb += self.spec_mem_rmask.eq(0)
        m.d.comb += self.spec_mem_wmask.eq(0)
        m.d.comb += self.spec_mem_wdata.eq(0)

        return m