UI: reducing CPU usage from 13% to 4% when offroad (#19575)

* Accurately control the UI frequency

* helper function sleep_for

selfdrive/common/utilpp.h

@@ -7,6 +7,8 @@
 #include <memory>
 #include <sstream>
 #include <fstream>
+#include <thread>
+#include <chrono>
 
 namespace util {
 
@@ -69,7 +71,9 @@ inline std::string getenv_default(const char* env_var, const char * suffix, cons
   }
 }
 
-
+inline void sleep_for(const int milliseconds) {
+  std::this_thread::sleep_for(std::chrono::milliseconds(milliseconds));
+}
 }
 
 struct unique_fd {

selfdrive/ui/android/ui.cc

@@ -148,7 +148,7 @@ int main(int argc, char* argv[]) {
 
   while (!do_exit) {
     if (!s->started) {
-      usleep(50 * 1000);
+      util::sleep_for(50);
     }
     double u1 = millis_since_boot();