diff --git a/insns/insn.py b/insns/insn.py
new file mode 100644
index 0000000..4588ff3
--- /dev/null
+++ b/insns/insn.py
@@ -0,0 +1,51 @@
+from nmigen import *
+
+class rvfi_insn(Elaboratable):
+    def __init__(self):
+        # Input ports
+        self.rvfi_valid = Signal(1)
+        self.rvfi_insn = Signal(32)
+        self.rvfi_pc_rdata = Signal(32)
+        self.rvfi_rs1_rdata = Signal(32)
+        self.rvfi_rs2_rdata = Signal(32)
+        self.rvfi_mem_rdata = Signal(32)
+
+        # Output ports
+        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(32)
+        self.spec_pc_wdata = Signal(32)
+        self.spec_mem_addr = Signal(32)
+        self.spec_mem_rmask = Signal(4)
+        self.spec_mem_wmask = Signal(4)
+        self.spec_mem_wdata = Signal(32)
+    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()
+
+        return m