Add reference to source of Tclktoq timing

diff --git a/techlibs/xilinx/abc_ff.v b/techlibs/xilinx/abc_ff.v
index 66d9573d37e3c929af9a25bcd450af1a8ed6c339..36e1a08e4d0d3dba8d83f6a83ac4e1dbb7ea997b 100644 (file)
--- a/techlibs/xilinx/abc_ff.v
+++ b/techlibs/xilinx/abc_ff.v
@@ -20,6 +20,8 @@
 
 // ============================================================================
 
+// Max delays from https://github.com/SymbiFlow/prjxray-db/blob/23c8b0851f979f0799318eaca90174413a46b257/artix7/timings/slicel.sdf#L237-L251
+
 module FDRE (output reg Q, input C, CE, D, R);
   parameter [0:0] INIT = 1'b0;
   parameter [0:0] IS_C_INVERTED = 1'b0;