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Merge pull request #1947 from whitequark/cxxrtl-usability

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cxxrtl: minor documentation and usability improvements
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whitequark 2020-04-16 21:28:13 +00:00 • committed by GitHub
commit b4b2345a10
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2 changed files with 19 additions and 10 deletions
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22
backends/cxxrtl/cxxrtl.cc
View file

@ -1166,8 +1166,7 @@ struct CxxrtlWorker {
});
dump_attrs(memory);
f << indent << (writable_memories[memory] ? "" : "const ")
<< "memory<" << memory->width << "> " << mangle(memory)
f << indent << "memory<" << memory->width << "> " << mangle(memory)
<< " { " << memory->size << "u";
if (init_cells.empty()) {
f << " };\n";
@ -1425,8 +1424,6 @@ struct CxxrtlWorker {
if (cell->getPort(ID(CLK)).is_wire())
register_edge_signal(sigmap, cell->getPort(ID(CLK)),
cell->parameters[ID(CLK_POLARITY)].as_bool() ? RTLIL::STp : RTLIL::STn);
// The $adff and $dffsr cells are level-sensitive, not edge-sensitive (in spite of the fact that they
// are inferred from an edge-sensitive Verilog process) and do not correspond to an edge-type sync rule.
}
// Similar for memory port cells.
if (cell->type.in(ID($memrd), ID($memwr))) {
@ -1642,21 +1639,30 @@ struct CxxrtlBackend : public Backend {
log("\n");
log(" write_cxxrtl [options] [filename]\n");
log("\n");
log("Write C++ code for simulating the design. The generated code requires a driver;\n");
log("the following simple driver is provided as an example:\n");
log("Write C++ code for simulating the design. The generated code requires a driver\n");
log("that instantiates the design, toggles its clock, and interacts with its ports.\n");
log("\n");
log("The following driver may be used as an example for a design with a single clock\n");
log("driving rising edge triggered flip-flops:\n");
log("\n");
log(" #include \"top.cc\"\n");
log("\n");
log(" int main() {\n");
log(" cxxrtl_design::p_top top;\n");
log(" while (1) {\n");
log(" top.p_clk.next = value<1> {1u};\n");
log(" top.step();\n");
log(" while (1) {\n");
log(" /* user logic */\n");
log(" top.p_clk.next = value<1> {0u};\n");
log(" top.step();\n");
log(" top.p_clk.next = value<1> {1u};\n");
log(" top.step();\n");
log(" }\n");
log(" }\n");
log("\n");
log("Note that CXXRTL simulations, just like the hardware they are simulating, are\n");
log("subject to race conditions. If, in then example above, the user logic would run\n");
log("simultaneously with the rising edge of the clock, the design would malfunction.\n");
log("\n");
log("The following options are supported by this backend:\n");
log("\n");
log(" -header\n");

7
backends/cxxrtl/cxxrtl.h
View file

@ -604,12 +604,15 @@ struct memory {
auto _ = {std::move(std::begin(init.data), std::end(init.data), data.begin() + init.offset)...};
}
value<Width> &operator [](size_t index) {
// An operator for direct memory reads. May be used at any time during the simulation.
const value<Width> &operator [](size_t index) const {
assert(index < data.size());
return data[index];
}
const value<Width> &operator [](size_t index) const {
// An operator for direct memory writes. May only be used before the simulation is started. If used
// after the simulation is started, the design may malfunction.
value<Width> &operator [](size_t index) {
assert(index < data.size());
return data[index];
}