From ae85698a2bf674e99c744169e56f8cbf2874778a Mon Sep 17 00:00:00 2001
From: Tom Verbeure <hombre+github@gmail.com>
Date: Thu, 9 Aug 2018 22:15:26 -0700
Subject: [PATCH] MulSimple

---
 .../vexriscv/plugin/MulSimplePlugin.scala     | 90 +++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 src/main/scala/vexriscv/plugin/MulSimplePlugin.scala

diff --git a/src/main/scala/vexriscv/plugin/MulSimplePlugin.scala b/src/main/scala/vexriscv/plugin/MulSimplePlugin.scala
new file mode 100644
index 0000000..41ed391
--- /dev/null
+++ b/src/main/scala/vexriscv/plugin/MulSimplePlugin.scala
@@ -0,0 +1,90 @@
+package vexriscv.plugin
+import vexriscv._
+import vexriscv.VexRiscv
+import spinal.core._
+
+class MulSimplePlugin extends Plugin[VexRiscv]{
+  object MUL_OPA extends Stageable(SInt(33 bits))
+  object MUL_OPB extends Stageable(SInt(33 bits))
+  object MUL     extends Stageable(Bits(64 bits))
+
+  object IS_MUL  extends Stageable(Bool)
+
+  override def setup(pipeline: VexRiscv): Unit = {
+    import Riscv._
+    import pipeline.config._
+
+
+    val actions = List[(Stageable[_ <: BaseType],Any)](
+      SRC1_CTRL                -> Src1CtrlEnum.RS,
+      SRC2_CTRL                -> Src2CtrlEnum.RS,
+      REGFILE_WRITE_VALID      -> True,
+      BYPASSABLE_EXECUTE_STAGE -> False,
+      BYPASSABLE_MEMORY_STAGE  -> False,
+      RS1_USE                  -> True,
+      RS2_USE                  -> True,
+      IS_MUL                   -> True
+    )
+
+    val decoderService = pipeline.service(classOf[DecoderService])
+    decoderService.addDefault(IS_MUL, False)
+    decoderService.add(List(
+      MULX  -> actions
+    ))
+
+  }
+
+  override def build(pipeline: VexRiscv): Unit = {
+    import pipeline._
+    import pipeline.config._
+
+    // Prepare signed inputs for the multiplier in the next stage.
+    // This will map them best to an FPGA DSP.
+    execute plug new Area {
+      import execute._
+      val aSigned,bSigned = Bool
+      val a,b = Bits(32 bit)
+
+      a := input(SRC1)
+      b := input(SRC2)
+      switch(input(INSTRUCTION)(13 downto 12)) {
+        is(B"01") {
+          aSigned := True
+          bSigned := True
+        }
+        is(B"10") {
+          aSigned := True
+          bSigned := False
+        }
+        default {
+          aSigned := False
+          bSigned := False
+        }
+      }
+
+      insert(MUL_OPA) := ((aSigned ? a.msb | False) ## a).asSInt
+      insert(MUL_OPB) := ((bSigned ? b.msb | False) ## b).asSInt
+    }
+
+    memory plug new Area {
+      import memory._
+
+      insert(MUL) := (input(MUL_OPA) * input(MUL_OPB))(63 downto 0).asBits
+    }
+
+    writeBack plug new Area {
+      import writeBack._
+
+      when(arbitration.isValid && input(IS_MUL)){
+        switch(input(INSTRUCTION)(13 downto 12)){
+          is(B"00"){
+            output(REGFILE_WRITE_DATA) := input(MUL)(31 downto 0)
+          }
+          is(B"01",B"10",B"11"){
+            output(REGFILE_WRITE_DATA) := input(MUL)(63 downto 32)
+          }
+        }
+      }
+    }
+  }
+}