Use the exposed Wait state in the C emulator to implement a wait loop.

This adds an option to configure the maximum steps to remain in the Wait state. This is currently only used for WFI, but the basic mechanism can be re-used for adding WRS.{STO, NTO} in the future.
riscv · Feb 27, 2025 · 8508843 · 8508843
1 parent 1147192
commit 8508843
Showing 1 changed file with 32 additions and 7 deletions.
diff --git a/c_emulator/riscv_sim.c b/c_emulator/riscv_sim.c
@@ -54,6 +54,7 @@ enum {
   OPT_ENABLE_ZICBOZ,
   OPT_ENABLE_SSTC,
   OPT_CACHE_BLOCK_SIZE,
+  OPT_MAX_WAIT_STEPS,
 };
 
 static bool do_show_times = false;
@@ -72,6 +73,8 @@ static int rvfi_dii_port;
 static int rvfi_dii_sock;
 #endif
 
+int max_wait_steps = 0;
+
 char *sig_file = NULL;
 uint64_t mem_sig_start = 0;
 uint64_t mem_sig_end = 0;
@@ -151,6 +154,7 @@ static struct option options[] = {
     {"enable-zicbom",               no_argument,       0, OPT_ENABLE_ZICBOM       },
     {"enable-zicboz",               no_argument,       0, OPT_ENABLE_ZICBOZ       },
     {"cache-block-size",            required_argument, 0, OPT_CACHE_BLOCK_SIZE    },
+    {"max-wait-steps",              required_argument, 0, OPT_MAX_WAIT_STEPS      },
 #ifdef SAILCOV
     {"sailcov-file",                required_argument, 0, 'c'                     },
 #endif
@@ -240,6 +244,7 @@ static int process_args(int argc, char **argv)
   uint64_t pmp_count = 0;
   uint64_t pmp_grain = 0;
   uint64_t block_size_exp = 0;
+  int wait_steps = 0;
   while (true) {
     c = getopt_long(argc, argv,
                     "a"
@@ -412,6 +417,15 @@ static int process_args(int argc, char **argv)
               block_size_exp, 1 << block_size_exp);
       rv_cache_block_size_exp = block_size_exp;
       break;
+    case OPT_MAX_WAIT_STEPS:
+      wait_steps = atoi(optarg);
+      if (wait_steps < 0) {
+        fprintf(stderr, "invalid max-wait-steps '%s' provided.\n", optarg);
+        exit(1);
+      }
+      fprintf(stderr, "setting max-wait-states to %d steps.\n", wait_steps);
+      max_wait_steps = wait_steps;
+      break;
     case 'x':
       fprintf(stderr, "enabling Zfinx support.\n");
       rv_enable_zfinx = true;
@@ -693,12 +707,13 @@ void rvfi_send_trace(unsigned version)
 void run_sail(void)
 {
   struct zstep_result step_result;
-  bool exit_wait = true;
+  bool exit_wait = (max_wait_steps > 0) ? false : true;
   bool diverged = false;
 
   /* initialize the step number */
   mach_int step_no = 0;
   int insn_cnt = 0;
+  int wait_steps = 0;
 #ifdef RVFI_DII
   bool need_instr = true;
 #endif
@@ -819,13 +834,23 @@ void run_sail(void)
       flush_logs();
       KILL(sail_int)(&sail_step);
     }
-    if (step_result.zstepped) {
-      if (config_print_step) {
-        fprintf(trace_log, "\n");
+    switch (step_result.zstate) {
+    case zSTEP_WAIT:
+      if (++wait_steps >= max_wait_steps)
+        exit_wait = true;
+      break;
+    case zSTEP_ACTIVE:
+      wait_steps = 0;
+      exit_wait = (max_wait_steps > 0) ? false : true;
+      if (step_result.zstepped) {
+        if (config_print_step) {
+          fprintf(trace_log, "\n");
+        }
+        step_no++;
+        insn_cnt++;
+        total_insns++;
       }
-      step_no++;
-      insn_cnt++;
-      total_insns++;
+      break;
     }
 
     if (do_show_times && (total_insns & 0xfffff) == 0) {