ESP8266: Support power on/off in custom wiring

In custom wiring, there can be a power pin to power on/off the modem. This
commit supports it and allows for the following configurations:

- power pin name
- power pin polarity
- power on/off delay time

components/wifi/esp8266-driver/ESP8266Interface.cpp

@@ -46,6 +46,10 @@
 #define MBED_CONF_ESP8266_RST NC
 #endif
 
+#ifndef MBED_CONF_ESP8266_PWR
+#define MBED_CONF_ESP8266_PWR NC
+#endif
+
 #define TRACE_GROUP  "ESPI" // ESP8266 Interface
 
 using namespace mbed;
@@ -55,6 +59,7 @@ using namespace rtos;
 ESP8266Interface::ESP8266Interface()
     : _esp(MBED_CONF_ESP8266_TX, MBED_CONF_ESP8266_RX, MBED_CONF_ESP8266_DEBUG, MBED_CONF_ESP8266_RTS, MBED_CONF_ESP8266_CTS),
       _rst_pin(MBED_CONF_ESP8266_RST), // Notice that Pin7 CH_EN cannot be left floating if used as reset
+      _pwr_pin(MBED_CONF_ESP8266_PWR),
       _ap_sec(NSAPI_SECURITY_UNKNOWN),
       _if_blocking(true),
       _if_connected(_cmutex),
@@ -87,9 +92,10 @@ ESP8266Interface::ESP8266Interface()
 #endif
 
 // ESP8266Interface implementation
-ESP8266Interface::ESP8266Interface(PinName tx, PinName rx, bool debug, PinName rts, PinName cts, PinName rst)
+ESP8266Interface::ESP8266Interface(PinName tx, PinName rx, bool debug, PinName rts, PinName cts, PinName rst, PinName pwr)
     : _esp(tx, rx, debug, rts, cts),
       _rst_pin(rst),
+      _pwr_pin(pwr),
       _ap_sec(NSAPI_SECURITY_UNKNOWN),
       _if_blocking(true),
       _if_connected(_cmutex),
@@ -134,6 +140,8 @@ ESP8266Interface::~ESP8266Interface()
 
     // Power down the modem
     _rst_pin.rst_assert();
+    // Power off the modem
+    _pwr_pin.power_off();
 }
 
 ESP8266Interface::ResetPin::ResetPin(PinName rst_pin) : _rst_pin(mbed::DigitalOut(rst_pin, 1))
@@ -162,6 +170,33 @@ bool ESP8266Interface::ResetPin::is_connected()
     return _rst_pin.is_connected();
 }
 
+ESP8266Interface::PowerPin::PowerPin(PinName pwr_pin) : _pwr_pin(mbed::DigitalOut(pwr_pin, !MBED_CONF_ESP8266_POWER_ON_POLARITY))
+{
+}
+
+void ESP8266Interface::PowerPin::power_on()
+{
+    if (_pwr_pin.is_connected()) {
+        _pwr_pin = MBED_CONF_ESP8266_POWER_ON_POLARITY;
+        tr_debug("HW power-on");
+        ThisThread::sleep_for(MBED_CONF_ESP8266_POWER_ON_TIME_MS);
+    }
+}
+
+void ESP8266Interface::PowerPin::power_off()
+{
+    if (_pwr_pin.is_connected()) {
+        _pwr_pin = !MBED_CONF_ESP8266_POWER_ON_POLARITY;
+        tr_debug("HW power-off");
+        ThisThread::sleep_for(MBED_CONF_ESP8266_POWER_OFF_TIME_MS);
+    }
+}
+
+bool ESP8266Interface::PowerPin::is_connected()
+{
+    return _pwr_pin.is_connected();
+}
+
 int ESP8266Interface::connect(const char *ssid, const char *pass, nsapi_security_t security,
                               uint8_t channel)
 {
@@ -347,6 +382,8 @@ int ESP8266Interface::disconnect()
 
     // Power down the modem
     _rst_pin.rst_assert();
+    // Power off the modem
+    _pwr_pin.power_off();
 
     return ret;
 }
@@ -425,6 +462,8 @@ bool ESP8266Interface::_get_firmware_ok()
 nsapi_error_t ESP8266Interface::_init(void)
 {
     if (!_initialized) {
+        _pwr_pin.power_off();
+        _pwr_pin.power_on();
         if (_reset() != NSAPI_ERROR_OK) {
             return NSAPI_ERROR_DEVICE_ERROR;
         }

components/wifi/esp8266-driver/ESP8266Interface.h

@@ -78,7 +78,7 @@ public:
      * @param rx        RX pin
      * @param debug     Enable debugging
      */
-    ESP8266Interface(PinName tx, PinName rx, bool debug = false, PinName rts = NC, PinName cts = NC, PinName rst = NC);
+    ESP8266Interface(PinName tx, PinName rx, bool debug = false, PinName rts = NC, PinName cts = NC, PinName rst = NC, PinName pwr = NC);
 
     /**
      * @brief ESP8266Interface default destructor
@@ -392,6 +392,16 @@ private:
         mbed::DigitalOut  _rst_pin;
     } _rst_pin;
 
+    // HW power pin
+    class PowerPin {
+    public:
+        PowerPin(PinName pwr_pin);
+        void power_on();
+        void power_off();
+        bool is_connected();
+    private:
+        mbed::DigitalOut  _pwr_pin;
+    } _pwr_pin;
 
     // Credentials
     static const int ESP8266_SSID_MAX_LENGTH = 32; /* 32 is what 802.11 defines as longest possible name */

components/wifi/esp8266-driver/mbed_lib.json

@@ -21,6 +21,23 @@
             "help": "RESET pin for the modem, defaults to Not Connected",
             "value": null
         },
+        "pwr": {
+            "help": "POWER pin for the modem, defaults to Not Connected",
+            "value": null
+        },
+        "power-on-polarity": {
+            "help": "Polarity of power-on for the modem. 0 means 0/1 for power on/off; 1 means 1/0 for power on/off.",
+            "options": [0, 1],
+            "value": 0
+        },
+        "power-on-time-ms": {
+            "help": "Delay after powering on the modem in ms",
+            "value": 3
+        },
+        "power-off-time-ms": {
+            "help": "Delay after powering off the modem in ms",
+            "value": 3
+        },
         "debug": {
             "help": "Enable debug logs. [true/false]",
             "value": false