GSM: modify begin() to allow setting bands

Author: Rocketct

libraries/GSM/examples/GSMClient/GSMClient.ino

@@ -11,14 +11,13 @@ char pass[]     = SECRET_PASSWORD;
 const char  server[] = "www.example.com";
 const char* ip_address;
 int port = 80;
-
 GSMClient client;
 
 void setup() {
   Serial.begin(115200);
   while(!Serial) {}
   Serial.println("Starting Carrier Network registration");
-  if(!GSM.begin(pin, apn, username, pass, CATNB)){
+  if(!GSM.begin(pin, apn, username, pass, CATNB, BAND_20 | BAND_19)){
     Serial.println("The board was not able to register to the network...");
     // do nothing forevermore:
     while(1);

libraries/GSM/src/GSM.cpp

@@ -26,7 +26,7 @@ mbed::CellularDevice *mbed::CellularDevice::get_default_instance()
     return &device;
 }
 
-int arduino::GSMClass::begin(const char* pin, const char* apn, const char* username, const char* password, RadioAccessTechnologyType rat, bool restart) {
+int arduino::GSMClass::begin(const char* pin, const char* apn, const char* username, const char* password, RadioAccessTechnologyType rat, uint32_t band, bool restart) {
 
   if(restart || isCmuxEnable()) {
     pinMode(PJ_10, OUTPUT);
@@ -69,9 +69,11 @@ int arduino::GSMClass::begin(const char* pin, const char* apn, const char* usern
   _username = username;
   _password = password;
   _rat = rat;
+  _band = (FrequencyBand) band;
   _context->set_credentials(apn, username, password);
 
   _context->set_access_technology(rat);
+  _context->set_band(_band);
 
   int connect_status = NSAPI_ERROR_AUTH_FAILURE;
   uint8_t retryCount = 0;

libraries/GSM/src/GSM.h

@@ -69,7 +69,7 @@ class GSMClass : public MbedSocketClass {
      * 
      * return: 0 in case of success, negative number in case of failure
      */
-  int begin(const char* pin, const char* apn, const char* username, const char* password, RadioAccessTechnologyType rat = CATNB, bool restart = true);
+  int begin(const char* pin, const char* apn, const char* username, const char* password, RadioAccessTechnologyType rat = CATNB, uint32_t band = BAND_20, bool restart = true);
 
   /*
      * Disconnect from the network
@@ -104,6 +104,7 @@ class GSMClass : public MbedSocketClass {
   const char* _password = nullptr;
   bool _cmuxGSMenable = _CMUX_ENABLE;
   RadioAccessTechnologyType _rat;
+  FrequencyBand _band;
   NetworkInterface* gsm_if = nullptr;
   mbed::CellularContext* _context = nullptr;
   mbed::CellularDevice* _device = nullptr;