Only search through newly detected devices and discard ones that disappeared

tmk_core/avr.mk

@@ -175,10 +175,11 @@ avrdude: $(BUILD_DIR)/$(TARGET).hex check-size
 		ls /dev/tty* > /tmp/1; \
 		echo -e "Detecting USB port, reset your controller now.\c"; \
 		while [ -z $$USB ]; do \
-			sleep 1; \
 			echo -e ".\c"; \
+			sleep 0.5; \
 			ls /dev/tty* > /tmp/2; \
-			USB=`diff /tmp/1 /tmp/2 | grep -o '/dev/tty.*'`; \
+			USB=`comm -13 /tmp/1 /tmp/2 | grep -o '/dev/tty.*'`; \
+			mv /tmp/2 /tmp/1; \
 		done; \
 		echo ""; \
 		echo "Detected controller on USB port at $$USB"; \