From: Michael Nolan <mtnolan2640@gmail.com>
Date: Mon, 1 Jun 2020 18:50:52 +0000 (-0400)
Subject: Add proof for RegFileArray
X-Git-Tag: div_pipeline~673
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=f21eeb4373b9da94a68c0d21044f2002c9ba03ab;p=soc.git

Add proof for RegFileArray
---

diff --git a/src/soc/regfile/formal/proof_regfile_array.py b/src/soc/regfile/formal/proof_regfile_array.py
new file mode 100644
index 00000000..b35c51eb
--- /dev/null
+++ b/src/soc/regfile/formal/proof_regfile_array.py
@@ -0,0 +1,123 @@
+# This is the proof for Regfile class from regfile/regfile.py
+
+from nmigen import (Module, Signal, Elaboratable, Mux, Cat, Repl,
+                    signed, ResetSignal, Array)
+from nmigen.asserts import (Assert, AnySeq, Assume, Cover, Initial,
+                            Rose, Fell, Stable, Past)
+from nmigen.test.utils import FHDLTestCase
+from nmigen.cli import rtlil
+import unittest
+
+from soc.regfile.regfile import RegFileArray
+
+
+class Driver(RegFileArray):
+    def __init__(self):
+        super().__init__(width=8, depth=4)
+        for i in range(1): # just do one for now
+            self.read_port(f"rd{i}")
+            self.write_port(f"wr{i}")
+
+    def elaborate(self, platform):
+        m = super().elaborate(platform)
+        comb = m.d.comb
+        sync = m.d.sync
+
+        width     = self.width
+        depth     = self.depth
+        _rdports  = self._rdports
+        _wrports  = self._wrports
+
+        comb += _wrports[0][1].data_i.eq(AnySeq(8))
+        comb += _wrports[0][1].wen.eq(AnySeq(depth))
+        comb += _rdports[0][1].ren.eq(AnySeq(depth))
+
+        rst = ResetSignal()
+
+        init = Initial()
+
+        # Most likely incorrect 4-way truth table
+        #
+        # rp.ren  wp.wen  rp.data_o            reg
+        # 0       0       zero                 should be previous value
+        # 0       1       zero                 wp.data_i
+        # 1       0       reg                  should be previous value
+        # 1       1       wp.data_i            wp.data_i
+
+        # Holds the value written to the register when a write happens
+        register_data = Array([Signal(self.width, name=f"reg_data{i}")
+                               for i in range(depth)])
+        register_written = Array([Signal(name=f"reg_written{i}")
+                                  for i in range(depth)])
+        comb += Cover(_rdports[0][1].ren == 0b0001)
+
+        with m.If(init):
+            comb += Assume(rst == 1)
+
+            for i in range(depth):
+                comb += Assume(register_written[i] == 0)
+
+        with m.Else():
+            comb += Assume(rst == 0)
+
+
+            # Assume that rd_en is onehot
+            bitsum = 0
+            for i in range(depth):
+                bitsum = bitsum + _rdports[0][1].ren[i]
+            comb += Assume(bitsum <= 1)
+
+
+
+            # If there is no read, then data_o should be 0
+            with m.If(_rdports[0][1].ren == 0):
+                comb += Assert(_rdports[0][1].data_o == 0)
+
+            # One of the rd_enable requests must be active
+            with m.Else():
+                for i in range(depth):
+                    # If there's a read on this register
+                    with m.If(_rdports[0][1].ren[i]):
+                        # Check to see if there's a write on this
+                        # cycle. If so, then the output data should be
+                        # that of the write port
+                        with m.If(_wrports[0][1].wen[i]):
+                            comb += Assert(_rdports[0][1].data_o ==
+                                           _wrports[0][1].data_i)
+                            comb += Cover(1)
+
+                        # Otherwise the data output should be the
+                        # saved register
+                        with m.Elif(register_written[i]):
+                            comb += Assert(_rdports[0][1].data_o ==
+                                           register_data[i])
+                            comb += Cover(1)
+
+            for i in range(depth):
+                # If there's a write to a given register, store that
+                # data in a copy of the register, and mark it as
+                # written
+                with m.If(_wrports[0][1].wen[i]):
+                    sync += register_data[i].eq(_wrports[0][1].data_i)
+                    sync += register_written[i].eq(1)
+                
+
+
+        return m
+
+
+class TestCase(FHDLTestCase):
+    def test_formal(self):
+        module = Driver()
+        self.assertFormal(module, mode="bmc", depth=10)
+        self.assertFormal(module, mode="cover", depth=10)
+
+    def test_ilang(self):
+        dut = Driver()
+        vl = rtlil.convert(dut, ports=[])
+        with open("regfile_array.il", "w") as f:
+            f.write(vl)
+
+
+if __name__ == '__main__':
+    unittest.main()