genlib/coding: gracefully handle flen(i) < 2

migen/genlib/coding.py

@@ -26,7 +26,7 @@ class Encoder(Module):
 	"""
 	def __init__(self, width):
 		self.i = Signal(width) # one-hot
-		self.o = Signal(max=width) # binary
+		self.o = Signal(max=max(2, width)) # binary
 		self.n = Signal() # invalid: none or multiple
 		act = dict((1<<j, self.o.eq(j)) for j in range(width))
 		act["default"] = self.n.eq(1)
@@ -54,7 +54,7 @@ class PriorityEncoder(Module):
 	"""
 	def __init__(self, width):
 		self.i = Signal(width) # one-hot, lsb has priority
-		self.o = Signal(max=width) # binary
+		self.o = Signal(max=max(2, width)) # binary
 		self.n = Signal() # none
 		for j in range(width)[::-1]: # last has priority
 			self.comb += If(self.i[j], self.o.eq(j))
@@ -82,7 +82,7 @@ class Decoder(Module):
 	"""
 
 	def __init__(self, width):
-		self.i = Signal(max=width) # binary
+		self.i = Signal(max=max(2, width)) # binary
 		self.n = Signal() # none/invalid
 		self.o = Signal(width) # one-hot
 		act = dict((j, self.o.eq(1<<j)) for j in range(width))

migen/test/test_coding.py

@@ -75,3 +75,28 @@ class DecCase(SimCase, unittest.TestCase):
 			else:
 				self.assertEqual(o, 1<<i)
 		self.run_with(cb, 256)
+
+class SmallPrioEncCase(SimCase, unittest.TestCase):
+	class TestBench(SimBench):
+		def __init__(self):
+			self.submodules.dut = PriorityEncoder(1)
+
+	def test_sizes(self):
+		self.assertEqual(flen(self.tb.dut.i), 1)
+		self.assertEqual(flen(self.tb.dut.o), 1)
+		self.assertEqual(flen(self.tb.dut.n), 1)
+
+	def test_run_sequence(self):
+		seq = list(range(1))
+		def cb(tb, tbp):
+			if seq:
+				tbp.dut.i = seq.pop(0)
+			i = tbp.dut.i
+			if tbp.dut.n:
+				self.assertEqual(i, 0)
+			else:
+				o = tbp.dut.o
+				if o > 0:
+					self.assertEqual(i & 1<<(o - 1), 0)
+				self.assertGreaterEqual(i, 1<<o)
+		self.run_with(cb, 5)