diff --git a/fpga_update/scripts/gen_update_mcs.py b/fpga_update/scripts/gen_update_mcs.py
index 62ba1ff..ef3b8c0 100644
--- a/fpga_update/scripts/gen_update_mcs.py
+++ b/fpga_update/scripts/gen_update_mcs.py
@@ -26,16 +26,6 @@ import subprocess
 import sys
 import tempfile
 
-REPO = r"E:\Xilinx_design\smod\SMOD_ATSC\my_exciter"
-TCL_DIR = os.path.join(REPO, "my_exciter.srcs", "tcl_1")
-BITSTREAM = os.path.join(REPO, "bitstream")
-IMPL = os.path.join(REPO, "my_exciter.runs", "impl_1")
-
-POST_BITSTREAM = os.path.join(TCL_DIR, "post_bitstream.tcl")
-GEN_RU = os.path.join(TCL_DIR, "runScript_GenRu.tcl")
-PERL_SCRIPT = os.path.join(TCL_DIR, "MakeSpiFlashProgrammerMcsFiles_backup.pl")
-
-
 def _env_lookup(key, default=None):
     """Machine-local values (paths, IPs) live in ~/skills_env.md, never in git.
     An OS environment variable of the same name overrides the file."""
@@ -56,6 +46,18 @@ def _env_lookup(key, default=None):
     return default
 
 
+# The my_exciter checkout root differs per machine; default keeps this machine's
+# historical path so behaviour is unchanged when the key is absent.
+REPO = _env_lookup("SMOD_REPO_ROOT", r"E:\Xilinx_design\smod\SMOD_ATSC\my_exciter")
+TCL_DIR = os.path.join(REPO, "my_exciter.srcs", "tcl_1")
+BITSTREAM = os.path.join(REPO, "bitstream")
+IMPL = os.path.join(REPO, "my_exciter.runs", "impl_1")
+
+POST_BITSTREAM = os.path.join(TCL_DIR, "post_bitstream.tcl")
+GEN_RU = os.path.join(TCL_DIR, "runScript_GenRu.tcl")
+PERL_SCRIPT = os.path.join(TCL_DIR, "MakeSpiFlashProgrammerMcsFiles_backup.pl")
+
+
 def resolve_vivado():
     """Vivado's install path differs per machine -- never hardcode it."""
     exe = _env_lookup("VIVADO_PATH")