Add ABC FAQ to "help abc"

Signed-off-by: Clifford Wolf <clifford@clifford.at>

diff --git a/passes/techmap/abc.cc b/passes/techmap/abc.cc
index be86f642a9a240d5161471e690c16fcf72fe512b..009ba6b9771a86c131cf13832d087358e5bc2fe5 100644 (file)
--- a/passes/techmap/abc.cc
+++ b/passes/techmap/abc.cc
@@ -1388,8 +1388,12 @@ struct AbcPass : public Pass {
                log("When neither -liberty nor -lut is used, the Yosys standard cell library is\n");
                log("loaded into ABC before the ABC script is executed.\n");
                log("\n");
-               log("This pass does not operate on modules with unprocessed processes in it.\n");
-               log("(I.e. the 'proc' pass should be used first to convert processes to netlists.)\n");
+               log("Note that this is a logic optimization pass within Yosys that is calling ABC\n");
+               log("internally. This is not going to \"run ABC on your design\". It will instead run\n");
+               log("ABC on logic snippets extracted from your design. You will not get any useful\n");
+               log("output when passing an ABC script that writes a file. Instead write your full\n");
+               log("design as BLIF file with write_blif and the load that into ABC externally if\n");
+               log("you want to use ABC to convert your design into another format.\n");
                log("\n");
                log("[1] http://www.eecs.berkeley.edu/~alanmi/abc/\n");
                log("\n");