Add pass to detect combinational loops

1 files changed, 127 insertions, 0 deletions

diff --git a/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala b/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala
new file mode 100644
index 00000000..16482560
--- /dev/null
+++ b/src/test/scala/firrtlTests/CheckCombLoopsSpec.scala
@@ -0,0 +1,127 @@
+// See LICENSE for license details.
+
+package firrtlTests
+
+import firrtl._
+import firrtl.ir._
+import firrtl.passes._
+import firrtl.Mappers._
+import annotations._
+
+class CheckCombLoopsSpec extends SimpleTransformSpec {
+
+  def emitter = new LowFirrtlEmitter
+
+  def transforms = Seq(
+    new ChirrtlToHighFirrtl,
+    new IRToWorkingIR,
+    new ResolveAndCheck,
+    new HighFirrtlToMiddleFirrtl,
+    new MiddleFirrtlToLowFirrtl
+  )
+
+  "Simple combinational loop" should "throw an exception" in {
+    val input = """circuit hasloops :
+                   |  module hasloops :
+                   |    input clk : Clock
+                   |    input a : UInt<1>
+                   |    input b : UInt<1>
+                   |    output c : UInt<1>
+                   |    output d : UInt<1>
+                   |    wire y : UInt<1>
+                   |    wire z : UInt<1>
+                   |    c <= b
+                   |    z <= y
+                   |    y <= z
+                   |    d <= z
+                   |""".stripMargin
+
+    val writer = new java.io.StringWriter
+    intercept[CheckCombLoops.CombLoopException] {
+      compile(CircuitState(parse(input), ChirrtlForm, None), writer)
+    }
+  }
+
+  "Node combinational loop" should "throw an exception" in {
+    val input = """circuit hasloops :
+                   |  module hasloops :
+                   |    input clk : Clock
+                   |    input a : UInt<1>
+                   |    input b : UInt<1>
+                   |    output c : UInt<1>
+                   |    output d : UInt<1>
+                   |    wire y : UInt<1>
+                   |    c <= b
+                   |    node z = and(c,y)
+                   |    y <= z
+                   |    d <= z
+                   |""".stripMargin
+
+    val writer = new java.io.StringWriter
+    intercept[CheckCombLoops.CombLoopException] {
+      compile(CircuitState(parse(input), ChirrtlForm, None), writer)
+    }
+  }
+
+  "Combinational loop through a combinational memory read port" should "throw an exception" in {
+    val input = """circuit hasloops :
+                   |  module hasloops :
+                   |    input clk : Clock
+                   |    input a : UInt<1>
+                   |    input b : UInt<1>
+                   |    output c : UInt<1>
+                   |    output d : UInt<1>
+                   |    wire y : UInt<1>
+                   |    wire z : UInt<1>
+                   |    c <= b
+                   |    mem m :
+                   |      data-type => UInt<1>
+                   |      depth => 2
+                   |      read-latency => 0
+                   |      write-latency => 1
+                   |      reader => r
+                   |      read-under-write => undefined
+                   |    m.r.clk <= clk
+                   |    m.r.addr <= y
+                   |    m.r.en <= UInt(1)
+                   |    z <= m.r.data
+                   |    y <= z
+                   |    d <= z
+                   |""".stripMargin
+
+    val writer = new java.io.StringWriter
+    intercept[CheckCombLoops.CombLoopException] {
+      compile(CircuitState(parse(input), ChirrtlForm, None), writer)
+    }
+  }
+
+  "Combination loop through an instance" should "throw an exception" in {
+    val input = """circuit hasloops :
+                   |  module thru :
+                   |    input in : UInt<1>
+                   |    output out : UInt<1>
+                   |    out <= in
+                   |  module hasloops :
+                   |    input clk : Clock
+                   |    input a : UInt<1>
+                   |    input b : UInt<1>
+                   |    output c : UInt<1>
+                   |    output d : UInt<1>
+                   |    wire y : UInt<1>
+                   |    wire z : UInt<1>
+                   |    c <= b
+                   |    inst inner of thru
+                   |    inner.in <= y
+                   |    z <= inner.out
+                   |    y <= z
+                   |    d <= z
+                   |""".stripMargin
+
+    val writer = new java.io.StringWriter
+    intercept[CheckCombLoops.CombLoopException] {
+      compile(CircuitState(parse(input), ChirrtlForm, None), writer)
+    }
+  }
+
+
+}