From b3c5ff7e95c768733e681967c0c0aa95d309f2b1 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Jean-Fran=C3=A7ois=20Nguyen?= <jf@lambdaconcept.com>
Date: Mon, 17 Jun 2019 20:01:26 +0200
Subject: [PATCH] vendor.xilinx_7series: fix IOB packing.

---
 nmigen/vendor/xilinx_7series.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/nmigen/vendor/xilinx_7series.py b/nmigen/vendor/xilinx_7series.py
index 0235896..a9836d9 100644
--- a/nmigen/vendor/xilinx_7series.py
+++ b/nmigen/vendor/xilinx_7series.py
@@ -121,6 +121,9 @@ class Xilinx7SeriesPlatform(TemplatedPlatform):
             for bit in range(len(q)):
                 _q = Signal()
                 _q.attrs["IOB"] = "TRUE"
+                # XXX: Vivado 2019.1 seems to make this flip-flop ineligible for IOB packing
+                # unless we prevent it from being optimized.
+                _q.attrs["DONT_TOUCH"] = "TRUE"
                 m.submodules += Instance("FDCE",
                     i_C=clk,
                     i_CE=Const(1),
-- 
2.30.2