migen: add patch to limit vivado threads to 1

artiq-fast/pkgs/migen-limit-vivado-threads-to-1.patch

@@ -0,0 +1,24 @@
+From 59a61be1b7b7cb45f5494b980b9f37e2838d6e6a Mon Sep 17 00:00:00 2001
+From: Astro <astro@spaceboyz.net>
+Date: Wed, 10 Jun 2020 19:29:25 +0200
+Subject: [PATCH] limit vivado threads to 1
+
+---
+ migen/build/xilinx/vivado.py | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/migen/build/xilinx/vivado.py b/migen/build/xilinx/vivado.py
+index d2cf101..e9e4b77 100644
+--- a/migen/build/xilinx/vivado.py
++++ b/migen/build/xilinx/vivado.py
+@@ -149,6 +149,7 @@ class XilinxVivadoToolchain:
+ 
+         # script that calls above steps
+         tcl = []
++        tcl.append("set_param general.maxThreads 1")
+         tcl.append("source \"{}_route.tcl\"".format(build_name))
+         tcl.append("source \"{}_bitstream.tcl\"".format(build_name))
+         tools.write_to_file(build_name + ".tcl", "\n".join(tcl))
+-- 
+2.26.2
+

artiq-fast/pkgs/python-deps.nix

@@ -86,6 +86,11 @@ rec {
       rev = "b1b2b298b85a795239daad84c75be073ddc4f8bd";
       sha256 = "1qy2ydk8xqqv92i992j1g71fbi185zd6s3kigzsf3169874dyh81";
     };
+    patches = [
+      # Vivado synthesis processes consume over 1 GB of RSS each. Limit them to
+      # 1 thread because they can become overwhelming during parallel builds.
+      ./migen-limit-vivado-threads-to-1.patch
+    ];
 
     propagatedBuildInputs = with python3Packages; [ colorama ];