add timing functions

src/main.c

@@ -5,6 +5,7 @@
  */
 
 #include <zephyr.h>
+#include <kernel.h>
 #include <console/console.h>
 #include <sys/printk.h>
 #include <tvm/runtime/micro/micro_rpc_server.h>
@@ -20,6 +21,68 @@ void TVMPlatformAbort(int error) {
   for (;;) ;
 }
 
+u32_t g_utvm_start_time;
+
+#define MILLIS_TIL_EXPIRY 200
+#define TIME_TIL_EXPIRY (K_MSEC(MILLIS_TIL_EXPIRY))
+K_TIMER_DEFINE(g_utvm_timer, /* expiry func */ NULL, /* stop func */ NULL);
+
+int g_utvm_timer_running = 0;
+
+int TVMPlatformTimerStart() {
+  if (g_utvm_timer_running) {
+    TVMLogf("timer already running");
+    return -1;
+  }
+  k_timer_start(&g_utvm_timer, TIME_TIL_EXPIRY, TIME_TIL_EXPIRY);
+  g_utvm_start_time = k_cycle_get_32();
+  g_utvm_timer_running = 1;
+  return 0;
+}
+
+int TVMPlatformTimerStop(double* res_us) {
+  if (!g_utvm_timer_running) {
+    TVMLogf("timer not running");
+    return -1;
+  }
+
+  u32_t stop_time = k_cycle_get_32();
+
+  // compute how long the work took
+  u32_t cycles_spent = stop_time - g_utvm_start_time;
+  if (stop_time < g_utvm_start_time) {
+      // we rolled over *at least* once, so correct the rollover it was *only*
+      // once, because we might still use this result
+      cycles_spent = ~((u32_t) 0) - (g_utvm_start_time - stop_time);
+  }
+
+  u32_t ns_spent = (u32_t) k_cyc_to_ns_floor64(cycles_spent);
+  double hw_clock_res_us = ns_spent / 1000.0;
+
+  // need to grab time remaining *before* stopping. when stopped, this function
+  // always returns 0.
+  s32_t time_remaining_ms = k_timer_remaining_get(&g_utvm_timer);
+  k_timer_stop(&g_utvm_timer);
+  // check *after* stopping to prevent extra expiries on the happy path
+  if (time_remaining_ms < 0) {
+    TVMLogf("negative time remaining");
+    return -1;
+  }
+  u32_t num_expiries = k_timer_status_get(&g_utvm_timer);
+  u32_t timer_res_ms = ((num_expiries * MILLIS_TIL_EXPIRY) + time_remaining_ms);
+  double approx_num_cycles = (double) k_ticks_to_cyc_floor32(1) * (double) k_ms_to_ticks_ceil32(timer_res_ms);
+  // if we approach the limits of the HW clock datatype (u32_t), use the
+  // coarse-grained timer result instead
+  if (approx_num_cycles > (0.5 * (~((u32_t) 0)))) {
+    *res_us = timer_res_ms * 1000.0;
+  } else {
+    *res_us = hw_clock_res_us;
+  }
+
+  g_utvm_timer_running = 0;
+  return 0;
+}
+
 #define WORKSPACE_SIZE_BYTES (120 * 1024)
 #define WORKSPACE_PAGE_SIZE_BYTES_LOG2 8