diff --git a/difftest/default.nix b/difftest/default.nix
index 621458011..2234a7ce6 100644
--- a/difftest/default.nix
+++ b/difftest/default.nix
@@ -6,13 +6,17 @@
 }:
 
 { outputName
-, emuType
-, buildType
+, emuType ? ""
+, moduleType
 , enableTrace ? false
 }:
 
-assert lib.assertMsg (lib.elem emuType [ "verilator" "vcs" ]) "emuType is either 'vcs' nor 'verilator'";
-assert lib.assertMsg (lib.elem buildType [ "t1" "t1rocket" ]) "emuType is either 't1' nor 't1rocket'";
+assert let
+  available = [ "dpi_t1" "dpi_t1rocket" "offline_t1" "offline_t1rocket" ];
+in
+lib.assertMsg (lib.elem moduleType available) "emuType is not in ${lib.concatStringsSep ", " available}";
+# if emuType is empty, then moduleType must be offline-*, or user should give valid emuType
+assert lib.assertMsg ((emuType == "" && lib.hasPrefix "offline" moduleType) || (lib.elem emuType [ "verilator" "vcs" ])) "emuType is either 'vcs' nor 'verilator'";
 
 rustPlatform.buildRustPackage {
   name = outputName;
@@ -31,8 +35,8 @@ rustPlatform.buildRustPackage {
     ];
   };
 
-  buildFeatures = [ "dpi_common/${emuType}" ] ++ lib.optionals enableTrace [ "dpi_common/trace" ];
-  buildAndTestSubdir = "./dpi_${buildType}";
+  buildFeatures = [ ] ++ lib.optionals (lib.hasPrefix "dpi" moduleType) [ "dpi_common/${emuType}" ] ++ lib.optionals enableTrace [ "dpi_common/trace" ];
+  buildAndTestSubdir = "./${moduleType}";
 
   env = {
     SPIKE_LIB_DIR = "${libspike}/lib";
@@ -47,7 +51,7 @@ rustPlatform.buildRustPackage {
   };
 
   passthru = {
-    dpiLibPath = "/lib/libdpi_${buildType}.a";
+    dpiLibPath = "/lib/libdpi_${moduleType}.a";
     inherit enableTrace;
   };
 }
diff --git a/difftest/offline-checker-t1.nix b/difftest/offline-checker-t1.nix
deleted file mode 100644
index bdb498074..000000000
--- a/difftest/offline-checker-t1.nix
+++ /dev/null
@@ -1,38 +0,0 @@
-{ lib
-, rustPlatform
-, libspike
-, libspike_interfaces
-, rtlDesignMetadata
-}:
-
-rustPlatform.buildRustPackage {
-  name = "offline-checker-t1";
-  src = with lib.fileset; toSource {
-    root = ./.;
-    fileset = unions [
-      ./spike_rs
-      ./offline_t1
-      ./dpi_common
-      ./dpi_t1
-      ./dpi_t1rocket
-      ./test_common
-      ./Cargo.lock
-      ./Cargo.toml
-    ];
-  };
-
-  buildFeatures = [ ];
-  buildAndTestSubdir = "./offline_t1";
-
-  env = {
-    SPIKE_LIB_DIR = "${libspike}/lib";
-    SPIKE_INTERFACES_LIB_DIR = "${libspike_interfaces}/lib";
-    DESIGN_VLEN = rtlDesignMetadata.vlen;
-    DESIGN_DLEN = rtlDesignMetadata.dlen;
-    SPIKE_ISA_STRING = rtlDesignMetadata.march;
-  };
-
-  cargoLock = {
-    lockFile = ./Cargo.lock;
-  };
-}
diff --git a/difftest/offline-checker-t1rocket.nix b/difftest/offline-checker-t1rocket.nix
deleted file mode 100644
index 76f6cc5ec..000000000
--- a/difftest/offline-checker-t1rocket.nix
+++ /dev/null
@@ -1,35 +0,0 @@
-{ lib
-, rustPlatform
-, libspike
-, libspike_interfaces
-, rtlDesignMetadata
-}:
-
-rustPlatform.buildRustPackage {
-  name = "offline-checker-t1rocket";
-  src = with lib.fileset; toSource {
-    root = ./.;
-    fileset = unions [
-      ./spike_rs
-      ./offline_t1rocket
-      ./test_common
-      ./Cargo.lock
-      ./Cargo.toml
-    ];
-  };
-
-  buildFeatures = [ ];
-  buildAndTestSubdir = "./offline_t1rocket";
-
-  env = {
-    SPIKE_LIB_DIR = "${libspike}/lib";
-    SPIKE_INTERFACES_LIB_DIR = "${libspike_interfaces}/lib";
-    DESIGN_VLEN = rtlDesignMetadata.vlen;
-    DESIGN_DLEN = rtlDesignMetadata.dlen;
-    SPIKE_ISA_STRING = rtlDesignMetadata.march;
-  };
-
-  cargoLock = {
-    lockFile = ./Cargo.lock;
-  };
-}
diff --git a/nix/t1/t1.nix b/nix/t1/t1.nix
index 51e31309f..3f6daa337 100644
--- a/nix/t1/t1.nix
+++ b/nix/t1/t1.nix
@@ -97,17 +97,17 @@ lib.mapAttrs
       # ---------------------------------------------------------------------------------
       # VERILATOR
       # ---------------------------------------------------------------------------------
-      makeDPI = ipScope.callPackage ../../difftest { };
+      makeDifftest = ipScope.callPackage ../../difftest { };
 
-      verilator-dpi-lib = ipScope.makeDPI {
+      verilator-dpi-lib = ipScope.makeDifftest {
         outputName = "t1-verilator-dpi-lib";
         emuType = "verilator";
-        buildType = "t1";
+        moduleType = "dpi_t1";
       };
-      verilator-dpi-lib-trace = ipScope.makeDPI {
+      verilator-dpi-lib-trace = ipScope.makeDifftest {
         outputName = "t1-verilator-trace-dpi-lib";
         emuType = "verilator";
-        buildType = "t1";
+        moduleType = "dpi_t1";
         enableTrace = true;
       };
 
@@ -126,16 +126,21 @@ lib.mapAttrs
       # ---------------------------------------------------------------------------------
       # VCS
       # ---------------------------------------------------------------------------------
-      vcs-dpi-lib = ipScope.makeDPI {
+      vcs-dpi-lib = ipScope.makeDifftest {
         outputName = "t1-vcs-dpi-lib";
         emuType = "vcs";
-        buildType = "t1";
+        moduleType = "dpi_t1";
       };
-      vcs-dpi-lib-trace = ipScope.makeDPI {
+      vcs-dpi-lib-trace = ipScope.makeDifftest {
         outputName = "t1-vcs-dpi-trace-lib";
         emuType = "vcs";
         enableTrace = true;
-        buildType = "t1";
+        moduleType = "dpi_t1";
+      };
+
+      offline-checker = ipScope.makeDifftest {
+        outputName = "t1-offline-checker";
+        moduleType = "offline_t1";
       };
 
       vcs-emu = t1Scope.sv-to-vcs-simulator {
@@ -150,8 +155,6 @@ lib.mapAttrs
         vcsLinkLibs = [ "${ipScope.vcs-dpi-lib-trace}/lib/libdpi_t1.a" ];
       };
 
-      offline-checker = ipScope.callPackage ../../difftest/offline-checker-t1.nix { };
-
       run = ipScope.callPackage ./run { };
     }); # end of ipScope
 
diff --git a/nix/t1/t1rocket.nix b/nix/t1/t1rocket.nix
index a00c017e0..14beac45d 100644
--- a/nix/t1/t1rocket.nix
+++ b/nix/t1/t1rocket.nix
@@ -41,14 +41,14 @@
       ];
     };
 
-    makeDPI = scope.callPackage ../../difftest { };
-    verilator-dpi-lib = scope.makeDPI {
+    mkDifftest = scope.callPackage ../../difftest { };
+    verilator-dpi-lib = scope.makeDifftest {
       outputName = "t1rocket-verilator-dpi-lib";
-      buildType = "t1rocket";
+      moduleType = "dpi_t1rocket";
     };
-    verilator-dpi-lib-trace = scope.makeDPI {
+    verilator-dpi-lib-trace = scope.makeDifftest {
       outputName = "t1rocket-verilator-trace-dpi-lib";
-      buildType = "t1rocket";
+      moduleType = "dpi_t1rocket";
       enableTrace = true;
     };
 
@@ -72,20 +72,23 @@
       ];
     };
 
-    offline-checker = scope.callPackage ../../difftest/offline-checker-t1rocket { };
-
-    vcs-dpi-lib = scope.makeDPI {
+    vcs-dpi-lib = scope.makeDifftest {
       outputName = "t1rocket-vcs-dpi-lib";
-      buildType = "t1rocket";
+      moduleType = "dpi_t1rocket";
       emuType = "vcs";
     };
-    vcs-dpi-lib-trace = scope.makeDPI {
+    vcs-dpi-lib-trace = scope.makeDifftest {
       outputName = "t1rocket-vcs-dpi-trace-lib";
-      buildType = "t1rocket";
+      moduleType = "dpi_t1rocket";
       emuType = "vcs";
       enableTrace = true;
     };
 
+    offline-checker = scope.makeDifftest {
+      outputName = "t1rocket-offline-checker";
+      moduleType = "offline_t1rocket";
+    };
+
     vcs-emu = sv-to-vcs-simulator {
       mainProgram = "t1rocket-vcs-simulator";
       rtl = scope.rtl;