From a6ab3264c7ffc66d702e543ee6ffceb97b8177c5 Mon Sep 17 00:00:00 2001
From: Donald Sebastian Leung <dl@m-labs.hk>
Date: Wed, 22 Jul 2020 11:55:26 +0800
Subject: [PATCH] Add BLT instruction for RV32I

---
 insns/insn_blt.py | 88 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 insns/insn_blt.py

diff --git a/insns/insn_blt.py b/insns/insn_blt.py
new file mode 100644
index 0000000..e5dda37
--- /dev/null
+++ b/insns/insn_blt.py
@@ -0,0 +1,88 @@
+from nmigen import *
+
+class rvfi_insn_blt(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()
+
+        # SB-type instruction format
+        insn_padding = Signal(self.RISCV_FORMAL_ILEN)
+        m.d.comb += insn_padding.eq(self.rvfi_insn >> 32)
+        insn_imm = Signal(self.RISCV_FORMAL_XLEN)
+        m.d.comb += insn_imm.eq(Value.as_signed(Cat(self.rvfi_insn[8:12], self.rvfi_insn[25:31], self.rvfi_insn[7], self.rvfi_insn[31]) << 1))
+        insn_rs2 = Signal(5)
+        m.d.comb += insn_rs2.eq(self.rvfi_insn[20:25])
+        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_opcode = Signal(7)
+        m.d.comb += insn_opcode.eq(self.rvfi_insn[:7])
+
+        misa_ok = Signal(1)
+        m.d.comb += misa_ok.eq(1)
+        ialign16 = Signal(1)
+        m.d.comb += ialign16.eq(0)
+
+        # BLT instruction
+        cond = Signal(1)
+        m.d.comb += cond.eq(Value.as_signed(self.rvfi_rs1_rdata) < Value.as_signed(self.rvfi_rs2_rdata))
+        next_pc = Signal(self.RISCV_FORMAL_XLEN)
+        m.d.comb += next_pc.eq(Mux(cond, self.rvfi_pc_rdata + insn_imm, self.rvfi_pc_rdata + 4))
+        m.d.comb += self.spec_valid.eq(self.rvfi_valid & (~insn_padding) & (insn_funct3 == 0b100) & (insn_opcode == 0b1100011))
+        m.d.comb += self.spec_rs1_addr.eq(insn_rs1)
+        m.d.comb += self.spec_rs2_addr.eq(insn_rs2)
+        m.d.comb += self.spec_pc_wdata.eq(next_pc)
+        m.d.comb += self.spec_trap.eq(Mux(ialign16, next_pc[0] != 0, next_pc[:2] != 0) | ~misa_ok)
+
+        # default assignments
+        m.d.comb += self.spec_rd_addr.eq(0)
+        m.d.comb += self.spec_rd_wdata.eq(0)
+        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