From 29bd81d66239b22ffdbe1f72416624823d712d34 Mon Sep 17 00:00:00 2001 From: whitequark Date: Fri, 12 Jun 2020 00:05:05 +0000 Subject: [PATCH] cxxrtl: unbuffer output wires of toplevel module. Without unbuffering output wires of, at least, toplevel modules, it is not possible to have most designs that rely on IO via toplevel ports (as opposed to using exclusively blackboxes) converge within one delta cycle. That seriously impairs the performance of CXXRTL. This commit avoids unbuffering outputs of all modules solely so that in future, CXXRTL could gain fully separate compilation, and not for any present technical reason. --- backends/cxxrtl/cxxrtl_backend.cc | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/backends/cxxrtl/cxxrtl_backend.cc b/backends/cxxrtl/cxxrtl_backend.cc index 0a810b8d1..c6b8bbc47 100644 --- a/backends/cxxrtl/cxxrtl_backend.cc +++ b/backends/cxxrtl/cxxrtl_backend.cc @@ -2154,7 +2154,7 @@ struct CxxrtlWorker { for (auto wire : module->wires()) { if (feedback_wires[wire]) continue; - if (wire->port_output) continue; + if (wire->port_output && !module->get_bool_attribute(ID::top)) continue; if (wire->name.begins_with("$") && !unbuffer_internal) continue; if (wire->name.begins_with("\\") && !unbuffer_public) continue; if (flow.wire_sync_defs.count(wire) > 0) continue;