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cxxrtl: only write VCD values that were actually updated. 

On a representative design (Minerva SoC) this reduces VCD file size
by ~20× and runtime by ~3×.
This commit is contained in:
whitequark 2020-06-06 21:55:53 +00:00
parent 9c36102669
commit 68362a9053
1 changed files with 30 additions and 10 deletions
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40
backends/cxxrtl/cxxrtl_vcd.h
View File

@ -28,10 +28,12 @@ class vcd_writer {
size_t ident;
size_t width;
chunk_t *curr;
size_t prev_off;
};
std::vector<std::string> current_scope;
std::vector<variable> variables;
std::vector<chunk_t> cache;
bool streaming = false;
void emit_timescale(unsigned number, const std::string &unit) {
@ -101,6 +103,22 @@ class vcd_writer {
buffer += '\n';
}
void append_variable(size_t width, chunk_t *curr) {
const size_t chunks = (width + (sizeof(chunk_t) * 8 - 1)) / (sizeof(chunk_t) * 8);
variables.emplace_back(variable { variables.size(), width, curr, cache.size() });
cache.insert(cache.end(), &curr[0], &curr[chunks]);
}
bool test_variable(const variable &var) {
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;
} else {
std::copy(&var.curr[0], &var.curr[chunks], &cache[var.prev_off]);
return true;
}
}
static std::vector<std::string> split_hierarchy(const std::string &hier_name) {
std::vector<std::string> hierarchy;
size_t prev = 0;
@ -133,11 +151,11 @@ public:
switch (item.type) {
// Not the best naming but oh well...
case debug_item::VALUE:
variables.emplace_back(variable { variables.size(), item.width, item.curr });
append_variable(item.width, item.curr);
emit_var(variables.back(), "wire", name);
break;
case debug_item::WIRE:
variables.emplace_back(variable { variables.size(), item.width, item.curr });
append_variable(item.width, item.curr);
emit_var(variables.back(), "reg", name);
break;
case debug_item::MEMORY: {
@ -145,7 +163,7 @@ public:
for (size_t index = 0; index < item.depth; index++) {
chunk_t *nth_curr = &item.curr[stride * index];
std::string nth_name = name + '[' + std::to_string(index) + ']';
variables.emplace_back(variable { variables.size(), item.width, nth_curr });
append_variable(item.width, nth_curr);
emit_var(variables.back(), "reg", nth_name);
}
break;
@ -175,17 +193,19 @@ public:
}
void sample(uint64_t timestamp) {
if (!streaming) {
bool first_sample = !streaming;
if (first_sample) {
emit_scope({});
emit_enddefinitions();
}
emit_time(timestamp);
for (auto var : variables) {
if (var.width == 1)
emit_scalar(var);
else
emit_vector(var);
}
for (auto var : variables)
if (test_variable(var) || first_sample) {
if (var.width == 1)
emit_scalar(var);
else
emit_vector(var);
}
}
};