diff --git a/.github/filters.yml b/.github/filters.yml
new file mode 100644
index 00000000..ee0eaa37
--- /dev/null
+++ b/.github/filters.yml
@@ -0,0 +1,20 @@
+cobble:
+  - 'tools/site_cobble/**/*'
+  - 'vnd/**/*'
+  - 'hdl/ip/bsv/**/*'
+  - 'hdl/projects/ecp5_evn/**/*'
+  - 'hdl/projects/gimlet/**/*'
+  - 'hdl/projects/icestick/**/*'
+  - 'hdl/projects/ignitionlet/**/*'
+  - 'hdl/projects/psc/**/*'
+  - 'hdl/projects/sidecar/**/*'
+  - 'hdl/projects/ulx3s/**/*'
+            
+buck2:
+  - 'vnd/xpm/**/*'
+  - 'prelude/**/*'
+  - 'toolchains/**/*'
+  - 'hdl/ip/toolchains/**/*'
+  - 'tools/**/*'
+  - 'hdl/ip/vhd/**/*'
+  - 'hdl/projects/grapefruit/**/*'
\ No newline at end of file
diff --git a/.github/workflows/simulation.yml b/.github/workflows/simulation.yml
new file mode 100644
index 00000000..421341bf
--- /dev/null
+++ b/.github/workflows/simulation.yml
@@ -0,0 +1,61 @@
+name: simulation
+run-name: ${{ github.actor }} running HDL simulations
+on:
+  [push]
+jobs:
+  changes:
+    runs-on: self-hosted
+    permissions:
+      pull-requests: read
+    outputs:
+      cobble: ${{ steps.changed_files.outputs.cobble }}
+      buck2: ${{ steps.changed_files.outputs.buck2 }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: 'true'
+      - uses: dorny/paths-filter@v3
+        id: filter
+        with:
+          filters: .github/filters.yml
+          
+  vunit-sim:
+    needs: changes
+    if: ${{ needs.changes.outputs.buck2 == 'true' }}
+    runs-on: self-hosted
+    steps:
+        - run: echo "The name of your branch is ${{ github.ref }} and your repository is ${{ github.repository }}."
+        - name: Check out repository code
+          uses: actions/checkout@v4
+          with:
+            submodules: 'true'
+        - name: Update pip reqs
+          run : python3 -m pip install --upgrade -r tools/requirements.txt --break-system-packages
+        - name: Run VUnit tests
+          run: buck2 bxl //tools/vunit-sims.bxl:vunit_sim_gen | while IFS= read -r line; do eval "$line" ; done
+  
+  bsv-sim:
+    # needs: changes
+    # if: ${{ needs.changes.outputs.cobble == 'true' }}
+    runs-on: self-hosted
+    steps:
+        - run: echo "The name of your branch is ${{ github.ref }} and your repository is ${{ github.repository }}."
+        - name: Check out repository code
+          uses: actions/checkout@v4
+          with:
+            submodules: 'true'
+            fetch-depth: 0
+        - name: Update pip reqs
+          run : python3 -m pip install --upgrade -r tools/requirements.txt --break-system-packages
+        - name: Env setup
+          run: cp BUILD.vars.gha BUILD.vars && echo "/opt/bsc-2022.01/bin" >> "$GITHUB_PATH"
+        - name: Restore build-dir
+          run: if [ -d /tmp/cobble_build_bkup ]; then cp -R /tmp/cobble_build_bkup ./build; else mkdir ./build; fi
+        - name: cobble init
+          run: ../vnd/cobble/cobble init .. --reinit
+          working-directory: ./build
+        - name: Run BSIM tests
+          run: ./cobble bluesim_test "//.*SchmittRegTest.*"
+          working-directory: ./build
+        - name: backup build-dir
+          run: cp -R ./build /tmp/cobble_build_bkup
\ No newline at end of file
diff --git a/.github/workflows/vunit.yml b/.github/workflows/vunit.yml
deleted file mode 100644
index 8164c37c..00000000
--- a/.github/workflows/vunit.yml
+++ /dev/null
@@ -1,18 +0,0 @@
-name: vunit
-run-name: ${{ github.actor }} is testing out GitHub Actions
-on:
-  [push]
-jobs:
-  Run-sim:
-    runs-on: self-hosted
-    steps:
-        - run: echo "The name of your branch is ${{ github.ref }} and your repository is ${{ github.repository }}."
-        - name: Check out repository code
-          uses: actions/checkout@v4
-          with:
-            submodules: 'true'
-        - name: Update pip reqs
-          run : python3 -m pip install --upgrade -r tools/requirements.txt --break-system-packages
-        - name: Run VUnit tests
-          run: buck2 bxl //tools/vunit-sims.bxl:vunit_sim_gen | while IFS= read -r line; do eval "$line" ; done
-        
\ No newline at end of file
diff --git a/BUILD.vars.gha b/BUILD.vars.gha
new file mode 100644
index 00000000..d9e6ab6b
--- /dev/null
+++ b/BUILD.vars.gha
@@ -0,0 +1,14 @@
+[bluespec]
+prefix = "/opt/bsc-2022.01"
+bin = "/opt/bsc-2022.01/bin/bsc"
+libdir = "/opt/bsc-2022.01/lib/"
+
+[yosys]
+bin = "/opt/oss-cad-suite-20240513/bin/yosys"
+libdir = "/opt/oss-cad-suite-20240513/share/yosys"
+
+[nextpnr]
+ecp5 = "/opt/oss-cad-suite-20240513/bin/nextpnr-ecp5"
+ecp5_pack = "/opt/oss-cad-suite-20240513/bin/ecppack"
+ice40 = "/opt/oss-cad-suite-20240513/bin/nextpnr-ice40"
+ice40_pack = "/opt/oss-cad-suite-20240513/bin/icepack"