quad: instruct virtual quad to relinquish cpu during I/O

quad/Makefile

@@ -38,9 +38,9 @@ test: all
 	$(MAKE) -C src/queue test
 	$(MAKE) -C src/computation_graph test
 	$(MAKE) -C src/quad_app test
-	# ruby scripts/tests/test_safety_checks.rb
-	# ruby scripts/tests/test_unix_uart.rb
-	# ruby scripts/tests/run_virtual_test_flight.rb
+	ruby scripts/tests/test_safety_checks.rb
+	ruby scripts/tests/test_unix_uart.rb
+	ruby scripts/tests/run_virtual_test_flight.rb
 
 clean:
 	rm -rf $(INCDIR) $(LIBDIR) $(OUTDIR) $(EXEDIR)

quad/src/virt_quad/hw_impl_unix_i2c.c

@@ -112,6 +112,7 @@ void * update_i2c_input_cache(void *arg) {
       cache[i].s = val;
       printf("%s: %ld\n", input_names[i], val);
     }
+    pthread_yield();
   }
   return NULL;
 }

quad/src/virt_quad/hw_impl_unix_mio7_led.c

@@ -52,6 +52,6 @@ void * output_cached_led() {
     sprintf(buff, "%d\n", on);
     write(fifo, buff, strlen(buff));
     close(fifo);
-    usleep(500); // don't spam the reader
+    pthread_yield();
   }
 }

quad/src/virt_quad/hw_impl_unix_pwm_input.c

@@ -78,6 +78,7 @@ void * update_input_cache(void *arg) {
 	printf("%s: Bad value - input not received\n", input_names[i]);
       }
     }
+    pthread_yield();
   }
   return NULL;
 }

quad/src/virt_quad/hw_impl_unix_pwm_output.c

@@ -59,7 +59,7 @@ void * output_cache(void *arg) {
     sprintf(buff, "%ld\n", cache[i]);
     write(fifo, buff, strlen(buff));
     close(fifo);
-    usleep(500); // don't spam the reader
+    pthread_yield();
   }
   return NULL;
 }