diff --git a/.gitmodules b/.gitmodules
index 65e1e71c9..76cae7242 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,9 @@
 [submodule "sky130/sky130_osu_sc_t12"]
 	path = sky130/sky130_osu_sc_t12
 	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_osu_sc_t12/
+[submodule "addins/riscv-arch-test"]
+	path = addins/riscv-arch-test
+	url = https://github.com/riscv-non-isa/riscv-arch-test.git
+[submodule "addins/riscv-isa-sim"]
+	path = addins/riscv-isa-sim
+	url = https://github.com/riscv-software-src/riscv-isa-sim
diff --git a/addins/riscv-isa-sim b/addins/riscv-isa-sim
new file mode 160000
index 000000000..6507ccc30
--- /dev/null
+++ b/addins/riscv-isa-sim
@@ -0,0 +1 @@
+Subproject commit 6507ccc30f29948a81661048e8a0ac3ae8e9a436