vivado: resolve install path from ~/skills_env.md instead of hardcoding D:\Xilinx

The Vivado install root differs per machine (C:\Xilinx here, D:\Xilinx on the
box these skills were written on), so every hardcoded path was already wrong
on this machine.

- new fpga_flash/scripts/vivado_env.py: resolves --vivado-dir > env var >
  VIVADO_ROOT (falling back to VIVADO_PATH) from ~/skills_env.md
- gen_mcs / program_flash / check_flash_csv: --vivado-dir now optional
- fpga_update/gen_update_mcs.py: same precedence for --vivado
- fpga_flash / smod_atsc_dev / vivado-prj-create SKILL.md: document the
  lookup instead of naming a drive letter
- skills_env template: VIVADO_ROOT/VIVADO_PATH are now blanks to fill in,
  so a new machine can't inherit a wrong default

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

fpga_flash/scripts/check_flash_csv.py

@@ -6,7 +6,8 @@ Checks whether 'w25q128bv-spi-x1_x2_x4' is present in Vivado's
 xicom_cfgmem_part_table.csv. If not, appends the correct row.
 
 Usage:
-    python check_flash_csv.py --vivado-dir "D:/Xilinx/Vivado/2018.1"
+    python check_flash_csv.py            # Vivado path from ~/skills_env.md
+    python check_flash_csv.py --vivado-dir "<install root>"   # or override it
 
 Exit codes:
     0 = device already present (no changes made)
@@ -17,6 +18,8 @@ import argparse
 import os
 import sys
 
+from vivado_env import resolve_vivado_dir
+
 DEVICE_NAME = "w25q128bv-spi-x1_x2_x4"
 # Fields: NAME, MEM_DEVICE, MEM_TYPE, MEM_DENSITY, DATA_WIDTH,
 #         MEM_MANUFACTURER, NUM_CFG_FILES, MEM_DEVICE_ALIAS, MEM_FAMILY
@@ -29,13 +32,14 @@ def main():
     )
     parser.add_argument(
         "--vivado-dir",
-        required=True,
-        help="Vivado install root, e.g. D:/Xilinx/Vivado/2018.1",
+        default=None,
+        help="Vivado install root; defaults to VIVADO_ROOT from ~/skills_env.md",
     )
     args = parser.parse_args()
 
     csv_path = os.path.join(
-        args.vivado_dir, "data", "xicom", "xicom_cfgmem_part_table.csv"
+        resolve_vivado_dir(args.vivado_dir),
+        "data", "xicom", "xicom_cfgmem_part_table.csv"
     )
     csv_path = csv_path.replace("\\", "/")
 

fpga_flash/scripts/gen_mcs.py

@@ -7,7 +7,6 @@ via -tclargs so no temporary script files are created.
 
 Usage:
     python gen_mcs.py \
-        --vivado-dir "D:/Xilinx/Vivado/2018.1" \
         --bit-file   "E:/project/RU_golden/RU_golden.runs/impl_1/RU_golden_top.bit" \
         --mcs-file   "E:/project/RU_golden/RU_golden.runs/impl_1/RU_golden_smod.mcs"
 
@@ -20,6 +19,8 @@ import os
 import subprocess
 import sys
 
+from vivado_env import resolve_vivado_dir
+
 
 def norm(path: str) -> str:
     """Normalize path to forward slashes (Vivado on Windows accepts both)."""
@@ -32,8 +33,8 @@ def main():
     )
     parser.add_argument(
         "--vivado-dir",
-        required=True,
-        help="Vivado install root, e.g. D:/Xilinx/Vivado/2018.1",
+        default=None,
+        help="Vivado install root; defaults to VIVADO_ROOT from ~/skills_env.md",
     )
     parser.add_argument(
         "--bit-file",
@@ -47,7 +48,7 @@ def main():
     )
     args = parser.parse_args()
 
-    vivado_dir = norm(args.vivado_dir)
+    vivado_dir = norm(resolve_vivado_dir(args.vivado_dir))
     bit_file = norm(args.bit_file)
     mcs_file = norm(args.mcs_file)
 

fpga_flash/scripts/program_flash.py

@@ -7,7 +7,6 @@ via -tclargs so no temporary script files are created.
 
 Usage:
     python program_flash.py \
-        --vivado-dir  "D:/Xilinx/Vivado/2018.1" \
         --flash-part  "w25q128bv-spi-x1_x2_x4" \
         --bit-file    "E:/project/impl_1/RU_golden_top.bit" \
         --mcs-file    "E:/project/impl_1/RU_golden_smod.mcs" \
@@ -29,6 +28,8 @@ import os
 import subprocess
 import sys
 
+from vivado_env import resolve_vivado_dir
+
 
 def norm(path: str) -> str:
     """Normalize path to forward slashes (Vivado on Windows accepts both)."""
@@ -41,8 +42,8 @@ def main():
     )
     parser.add_argument(
         "--vivado-dir",
-        required=True,
-        help="Vivado install root, e.g. D:/Xilinx/Vivado/2018.1",
+        default=None,
+        help="Vivado install root; defaults to VIVADO_ROOT from ~/skills_env.md",
     )
     parser.add_argument(
         "--flash-part",
@@ -66,7 +67,7 @@ def main():
     )
     args = parser.parse_args()
 
-    vivado_dir = norm(args.vivado_dir)
+    vivado_dir = norm(resolve_vivado_dir(args.vivado_dir))
     bit_file = norm(args.bit_file)
     mcs_file = norm(args.mcs_file)
     ltx_file = norm(args.ltx_file) if args.ltx_file else ""

fpga_flash/scripts/vivado_env.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Resolve the machine-local Vivado install path.
+
+The install path differs per machine (C:\\Xilinx here, D:\\Xilinx elsewhere), so it
+is never hardcoded in a skill. It lives in ~/skills_env.md, which stays out of git.
+Precedence: explicit --vivado-dir > OS env var > ~/skills_env.md.
+"""
+import os
+import re
+import sys
+
+
+def env_lookup(key, default=None):
+    """Read KEY from the OS environment, else from a `KEY = value` line in
+    ~/skills_env.md. Trailing `# comments` are stripped."""
+    v = os.environ.get(key)
+    if v:
+        return v
+    path = os.path.join(os.path.expanduser("~"), "skills_env.md")
+    try:
+        with open(path, encoding="utf-8") as f:
+            for line in f:
+                m = re.match(rf"\s*{re.escape(key)}\s*=\s*(.+?)\s*(?:#.*)?$", line)
+                if m:
+                    val = m.group(1).strip()
+                    # Placeholders like `<未安装>` mean "not configured on this machine".
+                    if val and not val.startswith("<"):
+                        return val
+    except OSError:
+        pass
+    return default
+
+
+def resolve_vivado_dir(cli_value=None):
+    """Vivado install ROOT (the dir containing bin/vivado.bat)."""
+    if cli_value:
+        return cli_value
+    root = env_lookup("VIVADO_ROOT")
+    if root:
+        return root
+    exe = env_lookup("VIVADO_PATH")
+    if exe:
+        # .../<root>/bin/vivado.bat -> <root>
+        return os.path.dirname(os.path.dirname(exe))
+    sys.exit(
+        "Vivado path not configured. Add `VIVADO_ROOT = <install root>` to "
+        "~/skills_env.md, set it as an env var, or pass --vivado-dir."
+    )
+
+
+def resolve_vivado_exe(cli_value=None):
+    """Full path to bin/vivado.bat."""
+    if cli_value:
+        return cli_value
+    exe = env_lookup("VIVADO_PATH")
+    if exe:
+        return exe
+    return os.path.join(resolve_vivado_dir(), "bin", "vivado.bat")