Add CLOCK_ERROR option to enable/disable feature (#4)

main/configuration.h

@@ -50,6 +50,10 @@ void ttn_register(void (*callback)(uint8_t message));
 // If using a single-channel gateway, uncomment this next option and set to your gateway's channel
 //#define SINGLE_CHANNEL_GATEWAY  0
 
+// If you are having difficulty sending messages to TTN after the first successful send,
+// uncomment the next option and experiment with values (~ 1 - 5)
+//#define CLOCK_ERROR             5
+
 #define DEBUG_PORT              Serial      // Serial debug port
 #define SERIAL_BAUD             115200      // Serial debug baud rate
 #define SLEEP_BETWEEN_MESSAGES  0           // Do sleep between messages

main/ttn.ino

@@ -143,7 +143,10 @@ bool ttn_setup() {
 void ttn_join() {
     // Reset the MAC state. Session and pending data transfers will be discarded.
     LMIC_reset();
-    LMIC_setClockError(MAX_CLOCK_ERROR * 5 / 100);
+
+    #ifdef CLOCK_ERROR
+    LMIC_setClockError(MAX_CLOCK_ERROR * CLOCK_ERROR / 100);
+    #endif
 
     #if defined(USE_ABP)