From 0955a603c889e3ce86ca65cf59ec3ca5650c6517 Mon Sep 17 00:00:00 2001 From: whitequark Date: Wed, 10 Jun 2020 14:39:45 +0000 Subject: [PATCH] cxxrtl: disambiguate values/wires and their aliases in debug info. With this change, it is easier to see which signals carry state (only wire<>s appear as `reg` in VCD files) and to construct a minimal checkpoint (CXXRTL_WIRE debug items represent the canonical smallest set of state required to fully reconstruct the simulation). --- backends/cxxrtl/cxxrtl.h | 29 ++++++++++++++++++++++++++++- backends/cxxrtl/cxxrtl_backend.cc | 2 +- backends/cxxrtl/cxxrtl_capi.h | 11 +++++++++-- backends/cxxrtl/cxxrtl_vcd.h | 17 ++++++++++++----- 4 files changed, 50 insertions(+), 9 deletions(-) diff --git a/backends/cxxrtl/cxxrtl.h b/backends/cxxrtl/cxxrtl.h index c988c9e80..bc3162981 100644 --- a/backends/cxxrtl/cxxrtl.h +++ b/backends/cxxrtl/cxxrtl.h @@ -716,6 +716,9 @@ struct metadata { typedef std::map metadata_map; +// Helper class to disambiguate values/wires and their aliases. +struct debug_alias {}; + // This structure is intended for consumption via foreign function interfaces, like Python's ctypes. // Because of this it uses a C-style layout that is easy to parse rather than more idiomatic C++. // @@ -726,6 +729,7 @@ struct debug_item : ::cxxrtl_object { VALUE = CXXRTL_VALUE, WIRE = CXXRTL_WIRE, MEMORY = CXXRTL_MEMORY, + ALIAS = CXXRTL_ALIAS, }; debug_item(const ::cxxrtl_object &object) : cxxrtl_object(object) {} @@ -748,7 +752,7 @@ struct debug_item : ::cxxrtl_object { type = VALUE; width = Bits; depth = 1; - curr = const_cast(item.data); + curr = const_cast(item.data); next = nullptr; } @@ -774,6 +778,29 @@ struct debug_item : ::cxxrtl_object { curr = item.data.empty() ? nullptr : item.data[0].data; next = nullptr; } + + template + debug_item(debug_alias, const value &item) { + static_assert(sizeof(item) == value::chunks * sizeof(chunk_t), + "value is not compatible with C layout"); + type = ALIAS; + width = Bits; + depth = 1; + curr = const_cast(item.data); + next = nullptr; + } + + template + debug_item(debug_alias, const wire &item) { + static_assert(sizeof(item.curr) == value::chunks * sizeof(chunk_t) && + sizeof(item.next) == value::chunks * sizeof(chunk_t), + "wire is not compatible with C layout"); + type = ALIAS; + width = Bits; + depth = 1; + curr = const_cast(item.curr.data); + next = nullptr; + } }; static_assert(std::is_standard_layout::value, "debug_item is not compatible with C layout"); diff --git a/backends/cxxrtl/cxxrtl_backend.cc b/backends/cxxrtl/cxxrtl_backend.cc index 785625f17..be73c9079 100644 --- a/backends/cxxrtl/cxxrtl_backend.cc +++ b/backends/cxxrtl/cxxrtl_backend.cc @@ -1646,7 +1646,7 @@ struct CxxrtlWorker { } else if (debug_alias_wires.count(wire)) { // Alias of a member wire f << indent << "items.emplace(path + " << escape_cxx_string(get_hdl_name(wire)); - f << ", debug_item(" << mangle(debug_alias_wires[wire]) << "));\n"; + f << ", debug_item(debug_alias(), " << mangle(debug_alias_wires[wire]) << "));\n"; count_alias_wires++; } else if (!localized_wires.count(wire)) { // Member wire diff --git a/backends/cxxrtl/cxxrtl_capi.h b/backends/cxxrtl/cxxrtl_capi.h index 46aa662b2..8bd906ea4 100644 --- a/backends/cxxrtl/cxxrtl_capi.h +++ b/backends/cxxrtl/cxxrtl_capi.h @@ -89,7 +89,14 @@ enum cxxrtl_type { // always NULL. CXXRTL_MEMORY = 2, - // More object types will be added in the future, but the existing ones will never change. + // Aliases correspond to netlist nodes driven by another node such that their value is always + // exactly equal, or driven by a constant value. + // + // Aliases can be inspected via the `curr` pointer. They cannot be modified, and the `next` + // pointer is always NULL. + CXXRTL_ALIAS = 3, + + // More object types may be added in the future, but the existing ones will never change. }; // Description of a simulated object. @@ -123,7 +130,7 @@ struct cxxrtl_object { uint32_t *curr; uint32_t *next; - // More description fields will be added in the future, but the existing ones will never change. + // More description fields may be added in the future, but the existing ones will never change. }; // Retrieve description of a simulated object. diff --git a/backends/cxxrtl/cxxrtl_vcd.h b/backends/cxxrtl/cxxrtl_vcd.h index f6b78bbf7..4c2021e92 100644 --- a/backends/cxxrtl/cxxrtl_vcd.h +++ b/backends/cxxrtl/cxxrtl_vcd.h @@ -104,13 +104,13 @@ class vcd_writer { buffer += '\n'; } - const variable ®ister_variable(size_t width, chunk_t *curr, bool immutable = false) { + const variable ®ister_variable(size_t width, chunk_t *curr, bool constant = false) { if (aliases.count(curr)) { return variables[aliases[curr]]; } else { const size_t chunks = (width + (sizeof(chunk_t) * 8 - 1)) / (sizeof(chunk_t) * 8); aliases[curr] = variables.size(); - if (immutable) { + if (constant) { variables.emplace_back(variable { variables.size(), width, curr, (size_t)-1 }); } else { variables.emplace_back(variable { variables.size(), width, curr, cache.size() }); @@ -122,7 +122,7 @@ class vcd_writer { bool test_variable(const variable &var) { if (var.prev_off == (size_t)-1) - return false; // immutable + return false; // constant const size_t chunks = (var.width + (sizeof(chunk_t) * 8 - 1)) / (sizeof(chunk_t) * 8); if (std::equal(&var.curr[0], &var.curr[chunks], &cache[var.prev_off])) { return false; @@ -164,7 +164,7 @@ public: switch (item.type) { // Not the best naming but oh well... case debug_item::VALUE: - emit_var(register_variable(item.width, item.curr, /*immutable=*/item.next == nullptr), "wire", name); + emit_var(register_variable(item.width, item.curr, /*constant=*/item.next == nullptr), "wire", name); break; case debug_item::WIRE: emit_var(register_variable(item.width, item.curr), "reg", name); @@ -178,6 +178,13 @@ public: } break; } + case debug_item::ALIAS: + // Like VALUE, but, even though `item.next == nullptr` always holds, the underlying value + // can actually change, and must be tracked. In most cases the VCD identifier will be + // unified with the aliased reg, but we should handle the case where only the alias is + // added to the VCD writer, too. + emit_var(register_variable(item.width, item.curr), "wire", name); + break; } } @@ -198,7 +205,7 @@ public: void add_without_memories(const debug_items &items) { this->template add(items, [](const std::string &, const debug_item &item) { - return item.type == debug_item::VALUE || item.type == debug_item::WIRE; + return item.type != debug_item::MEMORY; }); } -- 2.30.2