emu: support loading snapshot from command line

* But difftest is disabled when running with a snapshot. This will be
  fixed in the future.

Makefile

@@ -107,10 +107,11 @@ SEED ?= $(shell shuf -i 1-10000 -n 1)
 # use 'emu -h' to see more details
 B ?= 0
 E ?= -1
+#SNAPSHOT = --load-snapshot=$(NOOP_HOME)/build/2020-07-25@22:19:17.snapshot
 
 emu: $(EMU)
 ifeq ($(REMOTE),localhost)
-	@$(EMU) -i $(IMAGE) -s $(SEED) -b $(B) -e $(E)
+	@$(EMU) -i $(IMAGE) -s $(SEED) -b $(B) -e $(E) $(SNAPSHOT)
 else
 	ssh -tt $(REMOTE) "cd $(REMOTE_PRJ_HOME) && $(EMU) -i $(REMOTE_PREFIX)/$(realpath $(IMAGE)) -s $(SEED) -b $(B) -e $(E)"
 endif

src/test/csrc/emu.h

@@ -32,10 +32,10 @@ class Emulator {
   uint32_t seed;
   uint64_t max_cycles, cycles;
   uint64_t log_begin, log_end;
+  const char *snapshot_path;
 
   std::vector<const char *> parse_args(int argc, const char *argv[]);
 
-  static const struct option long_options[];
   static void print_help(const char *file);
 
   void read_emu_regs(uint64_t *r) {
@@ -76,7 +76,8 @@ class Emulator {
     image(nullptr),
     dut_ptr(new std::remove_reference<decltype(*dut_ptr)>::type),
     seed(0), max_cycles(-1), cycles(0),
-    log_begin(0), log_end(-1)
+    log_begin(0), log_end(-1),
+    snapshot_path(NULL)
   {
     // init emu
     auto args = parse_args(argc, argv);
@@ -88,10 +89,6 @@ class Emulator {
     srand48(seed);
     Verilated::randReset(2);
 
-    // set log time range and log level
-    dut_ptr->io_logCtrl_log_begin = log_begin;
-    dut_ptr->io_logCtrl_log_end = log_end;
-
     // init ram
     extern void init_ram(const char *img);
     init_ram(image);
@@ -235,6 +232,14 @@ class Emulator {
     eprintf(ANSI_COLOR_MAGENTA "This is random test for cache.\n" ANSI_COLOR_RESET);
     cache_test(max_cycles);
 #else
+    if (snapshot_path != NULL) {
+      snapshot_load(snapshot_path);
+    }
+
+    // set log time range and log level
+    dut_ptr->io_logCtrl_log_begin = log_begin;
+    dut_ptr->io_logCtrl_log_end = log_end;
+
     execute_cycles(max_cycles);
 #endif
   }

src/test/csrc/main.cpp

@@ -15,16 +15,6 @@
 std::function<double()> get_sc_time_stamp = []() -> double { return 0; };
 double sc_time_stamp() { return get_sc_time_stamp(); }
 
-const struct option Emulator::long_options[] = {
-  { "seed",           1, NULL, 's' },
-  { "max-cycles",     1, NULL, 'C' },
-  { "image",          1, NULL, 'i' },
-  { "log-begin",      1, NULL, 'b' },
-  { "log-end",        1, NULL, 'e' },
-  { "help",           0, NULL, 'h' },
-  { 0,                0, NULL,  0  }
-};
-
 void Emulator::print_help(const char *file) {
   printf("Usage: %s [OPTION...]\n", file);
   printf("\n");
@@ -39,9 +29,31 @@ void Emulator::print_help(const char *file) {
 
 std::vector<const char *> Emulator::parse_args(int argc, const char *argv[]) {
   std::vector<const char *> args = { argv[0] };
+  int long_index = 0;
+  const struct option long_options[] = {
+    { "load-snapshot",  1, NULL,  0  },
+    { "seed",           1, NULL, 's' },
+    { "max-cycles",     1, NULL, 'C' },
+    { "image",          1, NULL, 'i' },
+    { "log-begin",      1, NULL, 'b' },
+    { "log-end",        1, NULL, 'e' },
+    { "help",           0, NULL, 'h' },
+    { 0,                0, NULL,  0  }
+  };
+
   int o;
-  while ( (o = getopt_long(argc, const_cast<char *const*>(argv), "-s:C:hi:m:b:e:", long_options, NULL)) != -1) {
+  while ( (o = getopt_long(argc, const_cast<char *const*>(argv),
+          "-s:C:hi:m:b:e:", long_options, &long_index)) != -1) {
     switch (o) {
+      case 0:
+        if (long_index == 0) {
+          snapshot_path = optarg;
+          break;
+        }
+        // fall through
+      default:
+        print_help(argv[0]);
+        exit(0);
       case 's': 
         if(std::string(optarg) != "NO_SEED") {
           seed = atoll(optarg);
@@ -55,9 +67,6 @@ std::vector<const char *> Emulator::parse_args(int argc, const char *argv[]) {
                 break;
       case 'b': log_begin = atoll(optarg);  break;
       case 'e': log_end = atoll(optarg); break;
-      default:
-                print_help(argv[0]);
-                exit(0);
     }
   }