Adds check that AT firmware in use

ESP8266/ESP8266.cpp

@@ -57,6 +57,16 @@ ESP8266::ESP8266(PinName tx, PinName rx, bool debug, PinName rts, PinName cts)
     _parser.oob("UNLINK", callback(this, &ESP8266::_oob_socket_close_error));
 }
 
+bool ESP8266::at_available()
+{
+    _smutex.lock();
+    bool ready = _parser.send("AT")
+           && _parser.recv("OK\n");
+    _smutex.unlock();
+
+    return ready;
+}
+
 int ESP8266::get_firmware_version()
 {
     int version;

ESP8266/ESP8266.h

@@ -43,6 +43,13 @@ class ESP8266
 public:
     ESP8266(PinName tx, PinName rx, bool debug=false, PinName rts=NC, PinName cts=NC);
 
+    /**
+    * Check AT command interface of ESP8266
+    *
+    * @return true if ready to respond on AT commands
+    */
+    bool at_available(void);
+
     /**
     * Check firmware version of ESP8266
     *

ESP8266Interface.cpp

@@ -239,9 +239,9 @@ int ESP8266Interface::scan(WiFiAccessPoint *res, unsigned count)
 
 bool ESP8266Interface::_get_firmware_ok()
 {
-    if (_esp.get_firmware_version() != ESP8266_VERSION) {
+    if (_esp.get_firmware_version() < ESP8266_VERSION) {
         debug("ESP8266: ERROR: Firmware incompatible with this driver.\
-               \r\nUpdate to v%d - https://developer.mbed.org/teams/ESP8266/wiki/Firmware-Update\r\n",ESP8266_VERSION);
+               \r\nUpdate at least to v%d - https://developer.mbed.org/teams/ESP8266/wiki/Firmware-Update\r\n",ESP8266_VERSION);
         return false;
     }
 
@@ -267,6 +267,9 @@ bool ESP8266Interface::_disable_default_softap()
 nsapi_error_t ESP8266Interface::_init(void)
 {
     if (!_initialized) {
+        if (!_esp.at_available()) {
+            return NSAPI_ERROR_DEVICE_ERROR;
+        }
         if (!_esp.stop_uart_hw_flow_ctrl()) {
             return NSAPI_ERROR_DEVICE_ERROR;
         }