build: use default toolchain_path on all backend when passed value is None

litex/build/altera/quartus.py

@@ -117,7 +117,9 @@ fi
 
 class AlteraQuartusToolchain:
     def build(self, platform, fragment, build_dir="build", build_name="top",
-              toolchain_path="/opt/Altera", run=True, **kwargs):
+              toolchain_path=None, run=True, **kwargs):
+        if toolchain_path is None:
+            toolchain_path="/opt/Altera"
         cwd = os.getcwd()
         os.makedirs(build_dir, exist_ok=True)
         os.chdir(build_dir)

litex/build/lattice/diamond.py

@@ -132,7 +132,9 @@ class LatticeDiamondToolchain:
     special_overrides = common.lattice_ecpx_special_overrides
 
     def build(self, platform, fragment, build_dir="build", build_name="top",
-              toolchain_path="/opt/Diamond", run=True, **kwargs):
+              toolchain_path=None, run=True, **kwargs):
+        if toolchain_path is None:
+            toolchain_path = "/opt/Diamond"
         os.makedirs(build_dir, exist_ok=True)
         cwd = os.getcwd()
         os.chdir(build_dir)

litex/build/xilinx/vivado.py

@@ -214,7 +214,14 @@ class XilinxVivadoToolchain:
         )
 
     def build(self, platform, fragment, build_dir="build", build_name="top",
-            toolchain_path="/opt/Xilinx/Vivado", source=True, run=True):
+            toolchain_path=None, source=True, run=True):
+        if toolchain_path is None:
+            if sys.platform == "win32":
+                toolchain_path = "C:\\Xilinx\\Vivado"
+            elif sys.platform == "cygwin":
+                toolchain_path = "/cygdrive/c/Xilinx/Vivado"
+            else:
+                toolchain_path = "/opt/Xilinx/Vivado"
         os.makedirs(build_dir, exist_ok=True)
         cwd = os.getcwd()
         os.chdir(build_dir)