sim: make driving parts of a signal from distinct modules possible.

Fixes (part of) #1454.

amaranth/hdl/_xfrm.py

@@ -17,6 +17,7 @@
            "FragmentTransformer",
            "TransformedElaboratable",
            "DomainCollector", "DomainRenamer", "DomainLowerer",
+           "LHSMaskCollector",
            "ResetInserter", "EnableInserter"]
 
 
@@ -601,6 +602,71 @@ def on_fragment(self, fragment):
         return super().on_fragment(fragment)
 
 
+class LHSMaskCollector:
+    def __init__(self):
+        self.lhs = SignalDict()
+
+    def visit_stmt(self, stmt):
+        if type(stmt) is Assign:
+            self.visit_value(stmt.lhs, ~0)
+        elif type(stmt) is Switch:
+            for (_, substmt, _) in stmt.cases:
+                self.visit_stmt(substmt)
+        elif type(stmt) in (Property, Print):
+            pass
+        elif isinstance(stmt, Iterable):
+            for substmt in stmt:
+                self.visit_stmt(substmt)
+        else:
+            assert False # :nocov:
+
+    def visit_value(self, value, mask):
+        if type(value) in (Signal, ClockSignal, ResetSignal):
+            mask &= (1 << len(value)) - 1
+            self.lhs.setdefault(value, 0)
+            self.lhs[value] |= mask
+        elif type(value) is Operator:
+            assert value.operator in ("s", "u")
+            self.visit_value(value.operands[0], mask)
+        elif type(value) is Slice:
+            slice_mask = (1 << value.stop) - (1 << value.start)
+            mask <<= value.start
+            mask &= slice_mask
+            self.visit_value(value.value, mask)
+        elif type(value) is Part:
+            # Could be more accurate, but if you're relying on such details, you're not seeing
+            # the Light of Heaven.
+            self.visit_value(value.value, ~0)
+        elif type(value) is Concat:
+            for part in value.parts:
+                self.visit_value(part, mask)
+                mask >>= len(part)
+        elif type(value) is SwitchValue:
+            for (_, subvalue) in value.cases:
+                self.visit_value(subvalue, mask)
+        else:
+            assert False # :nocov:
+
+    def chunks(self):
+        for signal, mask in self.lhs.items():
+            if mask == (1 << len(signal)) - 1:
+                yield signal, 0, None
+            else:
+                start = 0
+                while start < len(signal):
+                    if ((mask >> start) & 1) == 0:
+                        start += 1
+                    else:
+                        stop = start
+                        while stop < len(signal) and ((mask >> stop) & 1) == 1:
+                            stop += 1
+                        yield (signal, start, stop)
+                        start = stop
+
+    def masks(self):
+        yield from self.lhs.items()
+
+
 class _ControlInserter(FragmentTransformer):
     def __init__(self, controls):
         self.src_loc = None
@@ -615,10 +681,9 @@ def on_fragment(self, fragment):
         for domain, statements in fragment.statements.items():
             if domain == "comb" or domain not in self.controls:
                 continue
-            signals = SignalSet()
-            for stmt in statements:
-                signals |= stmt._lhs_signals()
-            self._insert_control(new_fragment, domain, signals)
+            lhs_masks = LHSMaskCollector()
+            lhs_masks.visit_stmt(statements)
+            self._insert_control(new_fragment, domain, lhs_masks)
         return new_fragment
 
     def _insert_control(self, fragment, domain, signals):
@@ -630,13 +695,20 @@ def __call__(self, value, *, src_loc_at=0):
 
 
 class ResetInserter(_ControlInserter):
-    def _insert_control(self, fragment, domain, signals):
-        stmts = [s.eq(Const(s.init, s.shape())) for s in signals if not s.reset_less]
+    def _insert_control(self, fragment, domain, lhs_masks):
+        stmts = []
+        for signal, start, stop in lhs_masks.chunks():
+            if signal.reset_less:
+                continue
+            if start == 0 and stop is None:
+                stmts.append(signal.eq(Const(signal.init, signal.shape())))
+            else:
+                stmts.append(signal[start:stop].eq(Const(signal.init, signal.shape())[start:stop]))
         fragment.add_statements(domain, Switch(self.controls[domain], [(1, stmts, None)], src_loc=self.src_loc))
 
 
 class EnableInserter(_ControlInserter):
-    def _insert_control(self, fragment, domain, signals):
+    def _insert_control(self, fragment, domain, _lhs_masks):
         if domain in fragment.statements:
             fragment.statements[domain] = _StatementList([Switch(
                 self.controls[domain],

amaranth/sim/_base.py

@@ -23,7 +23,7 @@ class BaseSignalState:
     curr = NotImplemented
     next = NotImplemented
 
-    def update(self, value):
+    def update(self, value, mask=~0):
         raise NotImplementedError # :nocov:
 
 

amaranth/sim/_pyrtl.py

@@ -5,7 +5,7 @@
 
 from ..hdl import *
 from ..hdl._ast import SignalSet, _StatementList, Property
-from ..hdl._xfrm import ValueVisitor, StatementVisitor
+from ..hdl._xfrm import ValueVisitor, StatementVisitor, LHSMaskCollector
 from ..hdl._mem import MemoryInstance
 from ._base import BaseProcess
 from ._pyeval import value_to_string
@@ -487,19 +487,20 @@ def __call__(self, fragment):
         for domain_name in domains:
             domain_stmts = fragment.statements.get(domain_name, _StatementList())
             domain_process = PyRTLProcess(is_comb=domain_name == "comb")
-            domain_signals = domain_stmts._lhs_signals()
+            lhs_masks = LHSMaskCollector()
+            lhs_masks.visit_stmt(domain_stmts)
 
             if isinstance(fragment, MemoryInstance):
                 for port in fragment._read_ports:
                     if port._domain == domain_name:
-                        domain_signals.update(port._data._lhs_signals())
+                        lhs_masks.visit_value(port._data, ~0)
 
             emitter = _PythonEmitter()
             emitter.append(f"def run():")
             emitter._level += 1
 
             if domain_name == "comb":
-                for signal in domain_signals:
+                for (signal, _) in lhs_masks.masks():
                     signal_index = self.state.get_signal(signal)
                     self.state.slots[signal_index].is_comb = True
                     emitter.append(f"next_{signal_index} = {signal.init}")
@@ -533,7 +534,7 @@ def __call__(self, fragment):
                 if domain.async_reset and domain.rst is not None:
                     self.state.add_signal_waker(domain.rst, edge_waker(domain_process, 1))
 
-                for signal in domain_signals:
+                for (signal, _) in lhs_masks.masks():
                     signal_index = self.state.get_signal(signal)
                     emitter.append(f"next_{signal_index} = slots[{signal_index}].next")
 
@@ -546,7 +547,7 @@ def __call__(self, fragment):
                     emitter.append(f"if {rst}:")
                     with emitter.indent():
                         emitter.append("pass")
-                        for signal in domain_signals:
+                        for (signal, _) in lhs_masks.masks():
                             if not signal.reset_less:
                                 signal_index = self.state.get_signal(signal)
                                 emitter.append(f"next_{signal_index} = {signal.init}")
@@ -592,9 +593,11 @@ def __call__(self, fragment):
 
                             lhs(port._data)(data)
 
-            for signal in domain_signals:
+            for (signal, mask) in lhs_masks.masks():
+                if signal.shape().signed and (mask & 1 << (len(signal) - 1)):
+                    mask |= -1 << len(signal)
                 signal_index = self.state.get_signal(signal)
-                emitter.append(f"slots[{signal_index}].update(next_{signal_index})")
+                emitter.append(f"slots[{signal_index}].update(next_{signal_index}, {mask})")
 
             # There shouldn't be any exceptions raised by the generated code, but if there are
             # (almost certainly due to a bug in the code generator), use this environment variable

amaranth/sim/pysim.py

@@ -369,7 +369,8 @@ def add_waker(self, waker):
         assert waker not in self.wakers
         self.wakers.append(waker)
 
-    def update(self, value):
+    def update(self, value, mask=~0):
+        value = (self.next & ~mask) | (value & mask)
         if self.next != value:
             self.next = value
             self.pending.add(self)

tests/test_hdl_xfrm.py

@@ -227,6 +227,7 @@ def setUp(self):
         self.s1 = Signal()
         self.s2 = Signal(init=1)
         self.s3 = Signal(init=1, reset_less=True)
+        self.s4 = Signal(8, init=0x3a)
         self.c1 = Signal()
 
     def test_reset_default(self):
@@ -281,6 +282,40 @@ def test_reset_value(self):
         )
         """)
 
+    def test_reset_mask(self):
+        f = Fragment()
+        f.add_statements("sync", self.s4[2:4].eq(0))
+
+        f = ResetInserter(self.c1)(f)
+        self.assertRepr(f.statements["sync"], """
+        (
+            (eq (slice (sig s4) 2:4) (const 1'd0))
+            (switch (sig c1)
+                (case 1 (eq (slice (sig s4) 2:4) (slice (const 8'd58) 2:4)))
+            )
+        )
+        """)
+
+        f = Fragment()
+        f.add_statements("sync", self.s4[2:4].eq(0))
+        f.add_statements("sync", self.s4[3:5].eq(0))
+        f.add_statements("sync", self.s4[6:10].eq(0))
+
+        f = ResetInserter(self.c1)(f)
+        self.assertRepr(f.statements["sync"], """
+        (
+            (eq (slice (sig s4) 2:4) (const 1'd0))
+            (eq (slice (sig s4) 3:5) (const 1'd0))
+            (eq (slice (sig s4) 6:8) (const 1'd0))
+            (switch (sig c1)
+                (case 1 
+                    (eq (slice (sig s4) 2:5) (slice (const 8'd58) 2:5))
+                    (eq (slice (sig s4) 6:8) (slice (const 8'd58) 6:8))
+                )
+            )
+        )
+        """)
+
     def test_reset_less(self):
         f = Fragment()
         f.add_statements("sync", self.s3.eq(0))
@@ -423,3 +458,31 @@ def test_composition(self):
             )
         )
         """)
+
+class LHSMaskCollectorTestCase(FHDLTestCase):
+    def test_slice(self):
+        s = Signal(8)
+        lhs = LHSMaskCollector()
+        lhs.visit_value(s[2:5], ~0)
+        self.assertEqual(lhs.lhs[s], 0x1c)
+
+    def test_slice_slice(self):
+        s = Signal(8)
+        lhs = LHSMaskCollector()
+        lhs.visit_value(s[2:7][1:3], ~0)
+        self.assertEqual(lhs.lhs[s], 0x18)
+
+    def test_slice_concat(self):
+        s1 = Signal(8)
+        s2 = Signal(8)
+        lhs = LHSMaskCollector()
+        lhs.visit_value(Cat(s1, s2)[4:11], ~0)
+        self.assertEqual(lhs.lhs[s1], 0xf0)
+        self.assertEqual(lhs.lhs[s2], 0x07)
+
+    def test_slice_part(self):
+        s = Signal(8)
+        idx = Signal(8)
+        lhs = LHSMaskCollector()
+        lhs.visit_value(s.bit_select(idx, 5)[1:3], ~0)
+        self.assertEqual(lhs.lhs[s], 0xff)

tests/test_sim.py

@@ -1413,6 +1413,28 @@ async def testbench(ctx):
         with self.assertSimulation(Module(), traces=[mem1, mem2, mem3]) as sim:
             sim.add_testbench(testbench)
 
+    def test_multiple_modules(self):
+        m = Module()
+        m.submodules.m1 = m1 = Module()
+        m.submodules.m2 = m2 = Module()
+        a = Signal(8)
+        b = Signal(8)
+        m1.d.comb += b[0:2].eq(a[0:2])
+        m1.d.comb += b[4:6].eq(a[4:6])
+        m2.d.comb += b[2:4].eq(a[2:4])
+        m2.d.comb += b[6:8].eq(a[6:8])
+        with self.assertSimulation(m) as sim:
+            async def testbench(ctx):
+                ctx.set(a, 0)
+                self.assertEqual(ctx.get(b), 0)
+                ctx.set(a, 0x12)
+                self.assertEqual(ctx.get(b), 0x12)
+                ctx.set(a, 0x34)
+                self.assertEqual(ctx.get(b), 0x34)
+                ctx.set(a, 0xdb)
+                self.assertEqual(ctx.get(b), 0xdb)
+            sim.add_testbench(testbench)
+
 
 class SimulatorTracesTestCase(FHDLTestCase):
     def assertDef(self, traces, flat_traces):