perilus

commit b2e69ab264d590e195cbcb2044e37bbc03122987
parent 4083d01412cd28a59e85c0544abd420eafb3a880
Author: Bradley Gannon <bradley@bradleygannon.com>
Date:   Sat, 29 Nov 2025 15:21:05 -0500

Implement ExtendUnit

Diffstat:
M
shell.nix
 | 
1
+
M
src/main/scala/extendUnit.scala
 | 
24
+++++++++++++++++++++---
D
src/test/scala/.gitkeep
 | 
0

A
src/test/scala/perilus/extendUnit.scala
 | 
61
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

4 files changed, 83 insertions(+), 3 deletions(-)
diff --git a/shell.nix b/shell.nix
@@ -9,5 +9,6 @@ pkgs.mkShellNoCC {
     metals
     sbt
     scalafmt
+    verilator
   ];
 }
diff --git a/src/main/scala/extendUnit.scala b/src/main/scala/extendUnit.scala
@@ -1,15 +1,33 @@
 package com.rinthyAi.perilus.extendUnit
 
 import chisel3._
+import chisel3.util._
 
 class ExtendUnit extends Module {
   val io = IO(new Bundle {
-    val input = Input(UInt(21.W))
+    val input = Input(UInt(25.W))
     val immSrc = Input(UInt(2.W))
 
     val immExt = Output(UInt(32.W))
   })
 
-  // TODO implement
-  io.immExt := 0.U
+  // Table 7.1 (page 406)
+  when(io.immSrc === "b00".U) {
+    // I-type instruction
+    io.immExt := Cat(Fill(20, io.input(24)), io.input(24, 13))
+  }.elsewhen(io.immSrc === "b01".U) {
+    // S-type instruction
+    io.immExt := Cat(Fill(20, io.input(24)), io.input(24, 18), io.input(4, 0))
+  }.elsewhen(io.immSrc === "b10".U) {
+    // B-type instruction
+    io.immExt := Cat(
+      Fill(20, io.input(24)),
+      io.input(0),
+      io.input(23, 18),
+      io.input(4, 1),
+      0.U(1.W)
+    )
+  }.otherwise {
+    io.immExt := 0.U
+  }
 }
diff --git a/src/test/scala/.gitkeep b/src/test/scala/.gitkeep
diff --git a/src/test/scala/perilus/extendUnit.scala b/src/test/scala/perilus/extendUnit.scala
@@ -0,0 +1,61 @@
+import chisel3._
+import chisel3.simulator.scalatest.ChiselSim
+import org.scalatest.funspec.AnyFunSpec
+import com.rinthyAi.perilus.extendUnit._
+
+class ExtendUnitTests extends AnyFunSpec with ChiselSim {
+  describe("ExtendUnit") {
+    it("correctly extends I-type immediates") {
+      simulate(new ExtendUnit) { extendUnit =>
+        {
+          extendUnit.io.immSrc.poke("b00".U)
+
+          extendUnit.io.input.poke("hdc4691".U) // immediate value is 0xe9b
+          extendUnit.io.immExt.expect("h6e2".U)
+
+          extendUnit.io.input.poke("h1ff8946".U) // immediate value is 0xffc
+          extendUnit.io.immExt.expect("hfffffffc".U)
+        }
+      }
+    }
+    it("correctly extends S-type immediates") {
+      simulate(new ExtendUnit) { extendUnit =>
+        {
+          extendUnit.io.immSrc.poke("b01".U)
+
+          extendUnit.io.input.poke("h65b22a".U) // immediate value is 0x32a
+          extendUnit.io.immExt.expect("h32a".U)
+
+          extendUnit.io.input.poke("h1de532a".U) // immediate value is 0xeea
+          extendUnit.io.immExt.expect("hfffffeea".U)
+        }
+      }
+    }
+    it("correctly extends B-type immediates") {
+      simulate(new ExtendUnit) { extendUnit =>
+        {
+          extendUnit.io.immSrc.poke("b10".U)
+
+          extendUnit.io.input.poke("hcbee9".U) // immediate value is 0x868
+          extendUnit.io.immExt.expect("h868".U)
+
+          extendUnit.io.input.poke("h144ae93".U) // immediate value is 0x1a32
+          extendUnit.io.immExt.expect("hfffffa32".U)
+        }
+      }
+    }
+    it("outputs zero when immSrc is invalid") {
+      simulate(new ExtendUnit) { extendUnit =>
+        {
+          extendUnit.io.immSrc.poke("b11".U)
+
+          extendUnit.io.input.poke("hb2a945".U)
+          extendUnit.io.immExt.expect(0.U)
+
+          extendUnit.io.input.poke("h1f800d2".U)
+          extendUnit.io.immExt.expect(0.U)
+        }
+      }
+    }
+  }
+}