Add comment to xc7 box

diff --git a/techlibs/xilinx/abc_xc7.box b/techlibs/xilinx/abc_xc7.box
index 0a6a6eaf0fa5b7160b20e58b88865841151b05b0..b5817a6e0aa188698c0a12ae02a43ce4c15a417c 100644 (file)
--- a/techlibs/xilinx/abc_xc7.box
+++ b/techlibs/xilinx/abc_xc7.box
@@ -1,5 +1,8 @@
 # Max delays from https://github.com/SymbiFlow/prjxray-db/blob/34ea6eb08a63d21ec16264ad37a0a7b142ff6031/artix7/timings/CLBLL_L.sdf
 
+# NB: Inputs/Outputs must be ordered alphabetically
+#     (with exceptions for carry in/out)
+
 # F7BMUX slower than F7AMUX
 # Inputs: I0 I1 S0
 # Outputs: O