Cellular: added detach from the network.

Author: Teppo Järvelin

features/cellular/framework/API/CellularNetwork.h

@@ -284,6 +284,12 @@ class CellularNetwork : public NetworkInterface
      */
     virtual nsapi_error_t get_attach(AttachStatus &status) = 0;
 
+    /** Request detach from a network.
+     *
+     *  @return        zero on success
+     */
+    virtual nsapi_error_t detach() = 0;
+
     /** Get APN rate control.
      *
      *  @remark optional params are not updated if not received from network, so use good defaults

features/cellular/framework/AT/AT_CellularNetwork.cpp

@@ -733,7 +733,7 @@ bool AT_CellularNetwork::has_registration(RegistrationType reg_type)
     return true;
 }
 
-nsapi_error_t AT_CellularNetwork::set_attach(int timeout)
+nsapi_error_t AT_CellularNetwork::set_attach(int /*timeout*/)
 {
     _at.lock();
 
@@ -770,6 +770,19 @@ nsapi_error_t AT_CellularNetwork::get_attach(AttachStatus &status)
     return _at.unlock_return_error();
 }
 
+nsapi_error_t AT_CellularNetwork::detach()
+{
+    _at.lock();
+
+    tr_debug("Network detach");
+    _at.cmd_start("AT+CGATT=0");
+    _at.cmd_stop();
+    _at.resp_start();
+    _at.resp_stop();
+
+    return _at.unlock_return_error();
+}
+
 nsapi_error_t AT_CellularNetwork::get_apn_backoff_timer(int &backoff_timer)
 {
     // If apn is set

features/cellular/framework/AT/AT_CellularNetwork.h

@@ -74,6 +74,8 @@ class AT_CellularNetwork : public CellularNetwork, public AT_CellularBase
 
     virtual nsapi_error_t get_attach(AttachStatus &status);
 
+    virtual nsapi_error_t detach();
+
     virtual nsapi_error_t get_rate_control(CellularNetwork::RateControlExceptionReports &reports,
         CellularNetwork::RateControlUplinkTimeUnit &time_unit, int &uplink_rate);