diff --git a/README.md b/README.md
index 2b198c63b..776a7550d 100644
--- a/README.md
+++ b/README.md
@@ -48,19 +48,19 @@ Also known as latest git or master branch.
 
 ### Using PlatformIO
 
-[PlatformIO](https://platformio.org?utm_source=github&utm_medium=arduino-esp8266) is an open source ecosystem for IoT
+[PlatformIO](https://platformio.org?utm_source=arduino-esp8266) is an open source ecosystem for IoT
 development with a cross-platform build system, a library manager, and full support
 for Espressif (ESP8266) development. It works on the following popular host operating systems: macOS, Windows,
 Linux 32/64, and Linux ARM (like Raspberry Pi, BeagleBone, CubieBoard).
 
-- [What is PlatformIO?](https://docs.platformio.org/en/latest/what-is-platformio.html?utm_source=github&utm_medium=arduino-esp8266)
-- [PlatformIO IDE](https://platformio.org/platformio-ide?utm_source=github&utm_medium=arduino-esp8266)
-- [PlatformIO Core](https://docs.platformio.org/en/latest/core.html?utm_source=github&utm_medium=arduino-esp8266) (command line tool)
-- [Advanced usage](https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=github&utm_medium=arduino-esp8266) -
+- [What is PlatformIO?](https://docs.platformio.org/en/latest/what-is-platformio.html?utm_source=arduino-esp8266)
+- [PlatformIO IDE](https://platformio.org/platformio-ide?utm_source=arduino-esp8266)
+- [PlatformIO Core](https://docs.platformio.org/en/latest/core.html?utm_source=arduino-esp8266) (command line tool)
+- [Advanced usage](https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=arduino-esp8266) -
   custom settings, uploading to SPIFFS, Over-the-Air (OTA), staging version
-- [Integration with Cloud and Standalone IDEs](https://docs.platformio.org/en/latest/ide.html?utm_source=github&utm_medium=arduino-esp8266) -
+- [Integration with Cloud and Standalone IDEs](https://docs.platformio.org/en/latest/ide.html?utm_source=arduino-esp8266) -
   Cloud9, Codeanywhere, Eclipse Che (Codenvy), Atom, CLion, Eclipse, Emacs, NetBeans, Qt Creator, Sublime Text, VIM, Visual Studio, and VSCode
-- [Project Examples](https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=github&utm_medium=arduino-esp8266#examples)
+- [Project Examples](https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=arduino-esp8266#examples)
 
 ### Building with make
 
diff --git a/boards.txt b/boards.txt
index bcbf48813..9499d2354 100644
--- a/boards.txt
+++ b/boards.txt
@@ -625,6 +625,63 @@ esp8285.menu.eesz.1M.build.flash_ld=eagle.flash.1m.ld
 esp8285.menu.eesz.1M.build.spiffs_pagesize=256
 esp8285.menu.eesz.1M.upload.maximum_size=1023984
 esp8285.menu.eesz.1M.build.rfcal_addr=0xFC000
+esp8285.menu.eesz.2M64=2MB (FS:64KB OTA:~992KB)
+esp8285.menu.eesz.2M64.build.flash_size=2M
+esp8285.menu.eesz.2M64.build.flash_size_bytes=0x200000
+esp8285.menu.eesz.2M64.build.flash_ld=eagle.flash.2m64.ld
+esp8285.menu.eesz.2M64.build.spiffs_pagesize=256
+esp8285.menu.eesz.2M64.upload.maximum_size=1044464
+esp8285.menu.eesz.2M64.build.rfcal_addr=0x1FC000
+esp8285.menu.eesz.2M64.build.spiffs_start=0x1F0000
+esp8285.menu.eesz.2M64.build.spiffs_end=0x1FB000
+esp8285.menu.eesz.2M64.build.spiffs_blocksize=4096
+esp8285.menu.eesz.2M128=2MB (FS:128KB OTA:~960KB)
+esp8285.menu.eesz.2M128.build.flash_size=2M
+esp8285.menu.eesz.2M128.build.flash_size_bytes=0x200000
+esp8285.menu.eesz.2M128.build.flash_ld=eagle.flash.2m128.ld
+esp8285.menu.eesz.2M128.build.spiffs_pagesize=256
+esp8285.menu.eesz.2M128.upload.maximum_size=1044464
+esp8285.menu.eesz.2M128.build.rfcal_addr=0x1FC000
+esp8285.menu.eesz.2M128.build.spiffs_start=0x1E0000
+esp8285.menu.eesz.2M128.build.spiffs_end=0x1FB000
+esp8285.menu.eesz.2M128.build.spiffs_blocksize=4096
+esp8285.menu.eesz.2M256=2MB (FS:256KB OTA:~896KB)
+esp8285.menu.eesz.2M256.build.flash_size=2M
+esp8285.menu.eesz.2M256.build.flash_size_bytes=0x200000
+esp8285.menu.eesz.2M256.build.flash_ld=eagle.flash.2m256.ld
+esp8285.menu.eesz.2M256.build.spiffs_pagesize=256
+esp8285.menu.eesz.2M256.upload.maximum_size=1044464
+esp8285.menu.eesz.2M256.build.rfcal_addr=0x1FC000
+esp8285.menu.eesz.2M256.build.spiffs_start=0x1C0000
+esp8285.menu.eesz.2M256.build.spiffs_end=0x1FB000
+esp8285.menu.eesz.2M256.build.spiffs_blocksize=4096
+esp8285.menu.eesz.2M512=2MB (FS:512KB OTA:~768KB)
+esp8285.menu.eesz.2M512.build.flash_size=2M
+esp8285.menu.eesz.2M512.build.flash_size_bytes=0x200000
+esp8285.menu.eesz.2M512.build.flash_ld=eagle.flash.2m512.ld
+esp8285.menu.eesz.2M512.build.spiffs_pagesize=256
+esp8285.menu.eesz.2M512.upload.maximum_size=1044464
+esp8285.menu.eesz.2M512.build.rfcal_addr=0x1FC000
+esp8285.menu.eesz.2M512.build.spiffs_start=0x180000
+esp8285.menu.eesz.2M512.build.spiffs_end=0x1FA000
+esp8285.menu.eesz.2M512.build.spiffs_blocksize=8192
+esp8285.menu.eesz.2M1M=2MB (FS:1MB OTA:~512KB)
+esp8285.menu.eesz.2M1M.build.flash_size=2M
+esp8285.menu.eesz.2M1M.build.flash_size_bytes=0x200000
+esp8285.menu.eesz.2M1M.build.flash_ld=eagle.flash.2m1m.ld
+esp8285.menu.eesz.2M1M.build.spiffs_pagesize=256
+esp8285.menu.eesz.2M1M.upload.maximum_size=1044464
+esp8285.menu.eesz.2M1M.build.rfcal_addr=0x1FC000
+esp8285.menu.eesz.2M1M.build.spiffs_start=0x100000
+esp8285.menu.eesz.2M1M.build.spiffs_end=0x1FA000
+esp8285.menu.eesz.2M1M.build.spiffs_blocksize=8192
+esp8285.menu.eesz.2M=2MB (FS:none OTA:~1019KB)
+esp8285.menu.eesz.2M.build.flash_size=2M
+esp8285.menu.eesz.2M.build.flash_size_bytes=0x200000
+esp8285.menu.eesz.2M.build.flash_ld=eagle.flash.2m.ld
+esp8285.menu.eesz.2M.build.spiffs_pagesize=256
+esp8285.menu.eesz.2M.upload.maximum_size=1044464
+esp8285.menu.eesz.2M.build.rfcal_addr=0x1FC000
 esp8285.menu.led.2=2
 esp8285.menu.led.2.build.led=-DLED_BUILTIN=2
 esp8285.menu.led.0=0
diff --git a/cores/esp8266/Esp.cpp b/cores/esp8266/Esp.cpp
index a0e525f2b..db29ec599 100644
--- a/cores/esp8266/Esp.cpp
+++ b/cores/esp8266/Esp.cpp
@@ -193,9 +193,6 @@ bool EspClass::rtcUserMemoryWrite(uint32_t offset, uint32_t *data, size_t size)
     }
 }
 
-
-
-extern "C" void __real_system_restart_local();
 void EspClass::reset(void)
 {
     __real_system_restart_local();
@@ -267,11 +264,12 @@ uint8_t EspClass::getBootMode(void)
     return system_get_boot_mode();
 }
 
+#ifndef F_CPU
 uint8_t EspClass::getCpuFreqMHz(void)
 {
     return system_get_cpu_freq();
 }
-
+#endif
 
 uint32_t EspClass::getFlashChipId(void)
 {
diff --git a/cores/esp8266/Esp.h b/cores/esp8266/Esp.h
index f4529c839..01327747e 100644
--- a/cores/esp8266/Esp.h
+++ b/cores/esp8266/Esp.h
@@ -157,7 +157,14 @@ class EspClass {
         uint8_t getBootVersion();
         uint8_t getBootMode();
 
+#if defined(F_CPU) || defined(CORE_MOCK)
+        constexpr uint8_t getCpuFreqMHz() const
+        {
+            return clockCyclesPerMicrosecond();
+        }
+#else
         uint8_t getCpuFreqMHz();
+#endif
 
         uint32_t getFlashChipId();
         uint8_t getFlashChipVendorId();
@@ -201,6 +208,7 @@ class EspClass {
 };
 
 #ifndef CORE_MOCK
+
 uint32_t EspClass::getCycleCount()
 {
     return esp_get_cycle_count();
diff --git a/cores/esp8266/MD5Builder.cpp b/cores/esp8266/MD5Builder.cpp
index b32693ed7..3d068b949 100644
--- a/cores/esp8266/MD5Builder.cpp
+++ b/cores/esp8266/MD5Builder.cpp
@@ -1,10 +1,11 @@
 #include <Arduino.h>
 #include <MD5Builder.h>
+#include <memory>
 
-uint8_t hex_char_to_byte(uint8_t c){
-    return  (c >= 'a' && c <= 'f') ? (c - ((uint8_t)'a' - 0xa)) :
-            (c >= 'A' && c <= 'F') ? (c - ((uint8_t)'A' - 0xA)) :
-            (c >= '0' &&  c<= '9') ? (c - (uint8_t)'0') : 0;
+uint8_t hex_char_to_byte(uint8_t c) {
+    return (c >= 'a' && c <= 'f') ? (c - ((uint8_t)'a' - 0xa)) :
+           (c >= 'A' && c <= 'F') ? (c - ((uint8_t)'A' - 0xA)) :
+           (c >= '0' && c <= '9') ? (c - (uint8_t)'0') : 0;
 }
 
 void MD5Builder::begin(void){
@@ -18,25 +19,27 @@ void MD5Builder::add(const uint8_t * data, const uint16_t len){
 
 void MD5Builder::addHexString(const char * data){
     uint16_t i, len = strlen(data);
-    uint8_t * tmp = (uint8_t*)malloc(len/2);
-    if(tmp == NULL) {
+    auto tmp = std::unique_ptr<uint8_t[]>{new(std::nothrow) uint8_t[len / 2]};
+
+    if (!tmp) {
         return;
     }
+
     for(i=0; i<len; i+=2) {
         uint8_t high = hex_char_to_byte(data[i]);
         uint8_t low = hex_char_to_byte(data[i+1]);
         tmp[i/2] = (high & 0x0F) << 4 | (low & 0x0F);
     }
-    add(tmp, len/2);
-    free(tmp);
+    add(tmp.get(), len/2);
 }
 
-bool MD5Builder::addStream(Stream & stream, const size_t maxLen){
+bool MD5Builder::addStream(Stream &stream, const size_t maxLen) {
     const int buf_size = 512;
     int maxLengthLeft = maxLen;
-    uint8_t * buf = (uint8_t*) malloc(buf_size);
 
-    if(!buf) {
+    auto buf = std::unique_ptr<uint8_t[]>{new(std::nothrow) uint8_t[buf_size]};
+
+    if (!buf) {
         return false;
     }
 
@@ -45,21 +48,21 @@ bool MD5Builder::addStream(Stream & stream, const size_t maxLen){
 
         // determine number of bytes to read
         int readBytes = bytesAvailable;
-        if(readBytes > maxLengthLeft) {
-            readBytes = maxLengthLeft ;    // read only until max_len
+        if (readBytes > maxLengthLeft){
+            readBytes = maxLengthLeft;    // read only until max_len
         }
-        if(readBytes > buf_size) {
+        if (readBytes > buf_size){
             readBytes = buf_size;    // not read more the buffer can handle
         }
 
         // read data and check if we got something
-        int numBytesRead = stream.readBytes(buf, readBytes);
-        if(numBytesRead< 1) {
+        int numBytesRead = stream.readBytes(buf.get(), readBytes);
+        if (numBytesRead < 1) {
             return false;
         }
 
         // Update MD5 with buffer payload
-        MD5Update(&_ctx, buf, numBytesRead);
+        MD5Update(&_ctx, buf.get(), numBytesRead);
 
         yield();      // time for network streams
 
@@ -67,7 +70,7 @@ bool MD5Builder::addStream(Stream & stream, const size_t maxLen){
         maxLengthLeft -= numBytesRead;
         bytesAvailable = stream.available();
     }
-    free(buf);
+
     return true;
 }
 
@@ -75,17 +78,17 @@ void MD5Builder::calculate(void){
     MD5Final(_buf, &_ctx);
 }
 
-void MD5Builder::getBytes(uint8_t * output){
+void MD5Builder::getBytes(uint8_t * output) const {
     memcpy(output, _buf, 16);
 }
 
-void MD5Builder::getChars(char * output){
-    for(uint8_t i = 0; i < 16; i++) {
+void MD5Builder::getChars(char * output) const {
+    for (uint8_t i=0; i<16; i++){
         sprintf(output + (i * 2), "%02x", _buf[i]);
     }
 }
 
-String MD5Builder::toString(void){
+String MD5Builder::toString(void) const {
     char out[33];
     getChars(out);
     return String(out);
diff --git a/cores/esp8266/MD5Builder.h b/cores/esp8266/MD5Builder.h
index 6c6d560a0..c3fbce573 100644
--- a/cores/esp8266/MD5Builder.h
+++ b/cores/esp8266/MD5Builder.h
@@ -40,9 +40,9 @@ class MD5Builder {
     void addHexString(const String& data){ addHexString(data.c_str()); }
     bool addStream(Stream & stream, const size_t maxLen);
     void calculate(void);
-    void getBytes(uint8_t * output);
-    void getChars(char * output);
-    String toString(void);
+    void getBytes(uint8_t * output) const;
+    void getChars(char * output) const;
+    String toString(void) const;
 };
 
 
diff --git a/cores/esp8266/PolledTimeout.h b/cores/esp8266/PolledTimeout.h
index fe9c9ca4b..715564a8e 100644
--- a/cores/esp8266/PolledTimeout.h
+++ b/cores/esp8266/PolledTimeout.h
@@ -76,7 +76,7 @@ struct TimeSourceCycles
 
   using timeType = decltype(ESP.getCycleCount());
   static timeType time() {return ESP.getCycleCount();}
-  static constexpr timeType ticksPerSecond    = F_CPU;     // 80'000'000 or 160'000'000 Hz
+  static constexpr timeType ticksPerSecond    = ESP.getCpuFreqMHz() * 1000000UL;     // 80'000'000 or 160'000'000 Hz
   static constexpr timeType ticksPerSecondMax = 160000000; // 160MHz
 };
 
diff --git a/cores/esp8266/StackThunk.cpp b/cores/esp8266/StackThunk.cpp
index 541cd440f..4b708bcc6 100644
--- a/cores/esp8266/StackThunk.cpp
+++ b/cores/esp8266/StackThunk.cpp
@@ -26,6 +26,9 @@
 
 #include <stdint.h>
 #include <stdlib.h>
+#include <stdio.h>
+#include "pgmspace.h"
+#include "debug.h"
 #include "StackThunk.h"
 #include <ets_sys.h>
 
@@ -46,6 +49,11 @@ void stack_thunk_add_ref()
   stack_thunk_refcnt++;
   if (stack_thunk_refcnt == 1) {
     stack_thunk_ptr = (uint32_t *)malloc(_stackSize * sizeof(uint32_t));
+    if (!stack_thunk_ptr) {
+        // This is a fatal error, stop the sketch
+        DEBUGV("Unable to allocate BearSSL stack\n");
+        abort();
+    }
     stack_thunk_top = stack_thunk_ptr + _stackSize - 1;
     stack_thunk_save = NULL;
     stack_thunk_repaint();
diff --git a/cores/esp8266/Tone.cpp b/cores/esp8266/Tone.cpp
index 35a5a4151..ff895f153 100644
--- a/cores/esp8266/Tone.cpp
+++ b/cores/esp8266/Tone.cpp
@@ -22,6 +22,7 @@
 */
 
 #include "Arduino.h"
+#include "user_interface.h"
 #include "core_esp8266_waveform.h"
 
 // Which pins have a tone running on them?
@@ -35,10 +36,10 @@ static void _startTone(uint8_t _pin, uint32_t high, uint32_t low, unsigned long
 
   pinMode(_pin, OUTPUT);
 
-  high = std::max(high, (uint32_t)100);
-  low = std::max(low, (uint32_t)100);
+  high = std::max(high, (uint32_t)microsecondsToClockCycles(25));  // new 20KHz maximum tone frequency,
+  low = std::max(low, (uint32_t)microsecondsToClockCycles(25));   // (25us high + 25us low period = 20KHz)
 
-  if (startWaveform(_pin, high, low, (uint32_t) duration * 1000)) {
+  if (startWaveformCycles(_pin, high, low, microsecondsToClockCycles(duration * 1000))) {
     _toneMap |= 1 << _pin;
   }
 }
@@ -48,7 +49,7 @@ void tone(uint8_t _pin, unsigned int frequency, unsigned long duration) {
   if (frequency == 0) {
     noTone(_pin);
   } else {
-    uint32_t period = 1000000L / frequency;
+    uint32_t period = (1000000L * system_get_cpu_freq()) / frequency;
     uint32_t high = period / 2;
     uint32_t low = period - high;
     _startTone(_pin, high, low, duration);
@@ -62,7 +63,7 @@ void tone(uint8_t _pin, double frequency, unsigned long duration) {
   if (frequency < 1.0) { // FP means no exact comparisons
     noTone(_pin);
   } else {
-    double period = 1000000.0 / frequency;
+    double period = (1000000.0L * system_get_cpu_freq()) / frequency;
     uint32_t high = (uint32_t)((period / 2.0) + 0.5);
     uint32_t low = (uint32_t)(period + 0.5) - high;
     _startTone(_pin, high, low, duration);
diff --git a/cores/esp8266/Updater.cpp b/cores/esp8266/Updater.cpp
index 70d16a55e..351a57746 100644
--- a/cores/esp8266/Updater.cpp
+++ b/cores/esp8266/Updater.cpp
@@ -1,6 +1,7 @@
 #include "Updater.h"
 #include "eboot_command.h"
 #include <esp8266_peri.h>
+#include "StackThunk.h"
 
 //#define DEBUG_UPDATER Serial
 
@@ -40,6 +41,14 @@ UpdaterClass::UpdaterClass()
 {
 #if ARDUINO_SIGNING
   installSignature(&esp8266::updaterSigningHash, &esp8266::updaterSigningVerifier);
+  stack_thunk_add_ref();
+#endif
+}
+
+UpdaterClass::~UpdaterClass()
+{
+#if ARDUINO_SIGNING
+    stack_thunk_del_ref();
 #endif
 }
 
@@ -199,6 +208,7 @@ bool UpdaterClass::end(bool evenIfRemaining){
 #ifdef DEBUG_UPDATER
     DEBUG_UPDATER.println(F("no update"));
 #endif
+    _reset();
     return false;
   }
 
@@ -206,7 +216,6 @@ bool UpdaterClass::end(bool evenIfRemaining){
 #ifdef DEBUG_UPDATER
     DEBUG_UPDATER.printf_P(PSTR("premature end: res:%u, pos:%zu/%zu\n"), getError(), progress(), _size);
 #endif
-
     _reset();
     return false;
   }
@@ -226,6 +235,7 @@ bool UpdaterClass::end(bool evenIfRemaining){
 #endif
     if (sigLen != _verify->length()) {
       _setError(UPDATE_ERROR_SIGN);
+      _reset();
       return false;
     }
 
@@ -251,6 +261,7 @@ bool UpdaterClass::end(bool evenIfRemaining){
     uint8_t *sig = (uint8_t*)malloc(sigLen);
     if (!sig) {
       _setError(UPDATE_ERROR_SIGN);
+      _reset();
       return false;
     }
     ESP.flashRead(_startAddress + binSize, (uint32_t *)sig, sigLen);
@@ -262,9 +273,12 @@ bool UpdaterClass::end(bool evenIfRemaining){
     DEBUG_UPDATER.printf("\n");
 #endif
     if (!_verify->verify(_hash, (void *)sig, sigLen)) {
+      free(sig);
       _setError(UPDATE_ERROR_SIGN);
+      _reset();
       return false;
     }
+    free(sig);
 #ifdef DEBUG_UPDATER
     DEBUG_UPDATER.printf_P(PSTR("[Updater] Signature matches\n"));
 #endif
diff --git a/cores/esp8266/Updater.h b/cores/esp8266/Updater.h
index d47c61333..f51edc5b7 100644
--- a/cores/esp8266/Updater.h
+++ b/cores/esp8266/Updater.h
@@ -53,6 +53,7 @@ class UpdaterClass {
     typedef std::function<void(size_t, size_t)> THandlerFunction_Progress;
   
     UpdaterClass();
+    ~UpdaterClass();
 
     /* Optionally add a cryptographic signature verification hash and method */
     void installSignature(UpdaterHashClass *hash, UpdaterVerifyClass *verify) {  _hash = hash;  _verify = verify; }
diff --git a/cores/esp8266/core_esp8266_main.cpp b/cores/esp8266/core_esp8266_main.cpp
index a95c4b2c1..0ec4f1f3b 100644
--- a/cores/esp8266/core_esp8266_main.cpp
+++ b/cores/esp8266/core_esp8266_main.cpp
@@ -81,14 +81,25 @@ void initVariant() __attribute__((weak));
 void initVariant() {
 }
 
-void preloop_update_frequency() __attribute__((weak));
-void preloop_update_frequency() {
+extern "C" void __preloop_update_frequency() {
 #if defined(F_CPU) && (F_CPU == 160000000L)
-    REG_SET_BIT(0x3ff00014, BIT(0));
     ets_update_cpu_frequency(160);
+    CPU2X |= 1UL;
+#elif defined(F_CPU)
+    ets_update_cpu_frequency(80);
+    CPU2X &= ~1UL;
+#elif !defined(F_CPU)
+    if (system_get_cpu_freq() == 160) {
+        CPU2X |= 1UL;
+    }
+    else {
+        CPU2X &= ~1UL;
+    }
 #endif
 }
 
+extern "C" void preloop_update_frequency() __attribute__((weak, alias("__preloop_update_frequency")));
+
 extern "C" bool can_yield() {
   return cont_can_yield(g_pcont);
 }
diff --git a/cores/esp8266/core_esp8266_postmortem.cpp b/cores/esp8266/core_esp8266_postmortem.cpp
index 84aad50a0..2af579883 100644
--- a/cores/esp8266/core_esp8266_postmortem.cpp
+++ b/cores/esp8266/core_esp8266_postmortem.cpp
@@ -32,11 +32,10 @@
 #include "pgmspace.h"
 #include "gdb_hooks.h"
 #include "StackThunk.h"
+#include "coredecls.h"
 
 extern "C" {
 
-extern void __real_system_restart_local();
-
 // These will be pointers to PROGMEM const strings
 static const char* s_panic_file = 0;
 static int s_panic_line = 0;
diff --git a/cores/esp8266/core_esp8266_waveform.cpp b/cores/esp8266/core_esp8266_waveform.cpp
index 59fce8695..e3924cf08 100644
--- a/cores/esp8266/core_esp8266_waveform.cpp
+++ b/cores/esp8266/core_esp8266_waveform.cpp
@@ -112,15 +112,19 @@ void setTimer1Callback(uint32_t (*fn)()) {
 // waveform smoothly on next low->high transition.  For immediate change, stopWaveform()
 // first, then it will immediately begin.
 int startWaveform(uint8_t pin, uint32_t timeHighUS, uint32_t timeLowUS, uint32_t runTimeUS) {
-  if ((pin > 16) || isFlashInterfacePin(pin)) {
+  return startWaveformCycles(pin, microsecondsToClockCycles(timeHighUS), microsecondsToClockCycles(timeLowUS), microsecondsToClockCycles(runTimeUS));
+}
+
+int startWaveformCycles(uint8_t pin, uint32_t timeHighCycles, uint32_t timeLowCycles, uint32_t runTimeCycles) {
+   if ((pin > 16) || isFlashInterfacePin(pin)) {
     return false;
   }
   Waveform *wave = &waveform[pin];
   // Adjust to shave off some of the IRQ time, approximately
-  wave->nextTimeHighCycles = microsecondsToClockCycles(timeHighUS);
-  wave->nextTimeLowCycles = microsecondsToClockCycles(timeLowUS);
-  wave->expiryCycle = runTimeUS ? GetCycleCount() + microsecondsToClockCycles(runTimeUS) : 0;
-  if (runTimeUS && !wave->expiryCycle) {
+  wave->nextTimeHighCycles = timeHighCycles;
+  wave->nextTimeLowCycles = timeLowCycles;
+  wave->expiryCycle = runTimeCycles ? GetCycleCount() + runTimeCycles : 0;
+  if (runTimeCycles && !wave->expiryCycle) {
     wave->expiryCycle = 1; // expiryCycle==0 means no timeout, so avoid setting it
   }
 
diff --git a/cores/esp8266/core_esp8266_waveform.h b/cores/esp8266/core_esp8266_waveform.h
index 24ce91fb3..9a5f2ce37 100644
--- a/cores/esp8266/core_esp8266_waveform.h
+++ b/cores/esp8266/core_esp8266_waveform.h
@@ -50,6 +50,8 @@ extern "C" {
 // If runtimeUS > 0 then automatically stop it after that many usecs.
 // Returns true or false on success or failure.
 int startWaveform(uint8_t pin, uint32_t timeHighUS, uint32_t timeLowUS, uint32_t runTimeUS);
+// Same as above, but pass in CPU clock cycles instead of microseconds
+int startWaveformCycles(uint8_t pin, uint32_t timeHighCycles, uint32_t timeLowCycles, uint32_t runTimeCycles);
 // Stop a waveform, if any, on the specified pin.
 // Returns true or false on success or failure.
 int stopWaveform(uint8_t pin);
diff --git a/cores/esp8266/core_esp8266_wiring_digital.cpp b/cores/esp8266/core_esp8266_wiring_digital.cpp
index 47eeebf86..ab6ed5dee 100644
--- a/cores/esp8266/core_esp8266_wiring_digital.cpp
+++ b/cores/esp8266/core_esp8266_wiring_digital.cpp
@@ -235,21 +235,23 @@ extern void __attachInterrupt(uint8_t pin, voidFuncPtr userFunc, int mode)
     __attachInterruptFunctionalArg(pin, (voidFuncPtrArg)userFunc, 0, mode, false);
 }
 
+extern void __resetPins() {
+  for (int i = 0; i <= 16; ++i) {
+    if (!isFlashInterfacePin(i))
+        pinMode(i, INPUT);
+  }
+}
+
 extern void initPins() {
   //Disable UART interrupts
   system_set_os_print(0);
   U0IE = 0;
   U1IE = 0;
 
-  for (int i = 0; i <= 5; ++i) {
-    pinMode(i, INPUT);
-  }
-  // pins 6-11 are used for the SPI flash interface
-  for (int i = 12; i <= 16; ++i) {
-    pinMode(i, INPUT);
-  }
+  resetPins();
 }
 
+extern void resetPins() __attribute__ ((weak, alias("__resetPins")));
 extern void pinMode(uint8_t pin, uint8_t mode) __attribute__ ((weak, alias("__pinMode")));
 extern void digitalWrite(uint8_t pin, uint8_t val) __attribute__ ((weak, alias("__digitalWrite")));
 extern int digitalRead(uint8_t pin) __attribute__ ((weak, alias("__digitalRead"), nothrow));
diff --git a/cores/esp8266/core_esp8266_wiring_pwm.cpp b/cores/esp8266/core_esp8266_wiring_pwm.cpp
index 5a3481bbd..b15b95f82 100644
--- a/cores/esp8266/core_esp8266_wiring_pwm.cpp
+++ b/cores/esp8266/core_esp8266_wiring_pwm.cpp
@@ -25,6 +25,7 @@
 #include "core_esp8266_waveform.h"
 
 extern "C" {
+#include "user_interface.h"
 
 static uint32_t analogMap = 0;
 static int32_t analogScale = PWMRANGE;
@@ -50,7 +51,7 @@ extern void __analogWrite(uint8_t pin, int val) {
   if (pin > 16) {
     return;
   }
-  uint32_t analogPeriod = 1000000L / analogFreq;
+  uint32_t analogPeriod = (1000000L * system_get_cpu_freq()) / analogFreq;
   if (val < 0) {
     val = 0;
   } else if (val > analogScale) {
@@ -68,7 +69,7 @@ extern void __analogWrite(uint8_t pin, int val) {
     stopWaveform(pin);
     digitalWrite(pin, LOW);
   } else {
-    if (startWaveform(pin, high, low, 0)) {
+    if (startWaveformCycles(pin, high, low, 0)) {
       analogMap |= (1 << pin);
     }
   }
diff --git a/cores/esp8266/coredecls.h b/cores/esp8266/coredecls.h
index 86ba43711..aa37cb06b 100644
--- a/cores/esp8266/coredecls.h
+++ b/cores/esp8266/coredecls.h
@@ -21,6 +21,7 @@ void esp_schedule();
 void tune_timeshift64 (uint64_t now_us);
 void disable_extra4k_at_link_time (void) __attribute__((noinline));
 bool sntp_set_timezone_in_seconds(int32_t timezone);
+void __real_system_restart_local() __attribute__((noreturn));
 
 uint32_t sqrt32 (uint32_t n);
 uint32_t crc32 (const void* data, size_t length, uint32_t crc = 0xffffffff);
diff --git a/cores/esp8266/wiring_private.h b/cores/esp8266/wiring_private.h
index 2c53565a6..cb52f0539 100644
--- a/cores/esp8266/wiring_private.h
+++ b/cores/esp8266/wiring_private.h
@@ -37,6 +37,7 @@ extern "C" {
 typedef void (*voidFuncPtr)(void);
 
 void initPins();
+void resetPins();
 
 #ifdef __cplusplus
 } // extern "C"
diff --git a/doc/installing.rst b/doc/installing.rst
index ca9e3f449..515fc891f 100644
--- a/doc/installing.rst
+++ b/doc/installing.rst
@@ -230,3 +230,20 @@ Instructions - Other OS
        cd hardware\esp8266com\esp8266
        git status
        git pull
+
+Using PlatformIO
+----------------
+
+`PlatformIO <https://platformio.org?utm_source=arduino-esp8266>`__
+is an open source ecosystem for IoT development with a cross-platform
+build system, a library manager, and full support for Espressif
+(ESP8266) development. It works on the following popular host operating
+systems: macOS, Windows, Linux 32/64, and Linux ARM (like Raspberry Pi,
+BeagleBone, CubieBoard).
+
+- `What is PlatformIO? <https://docs.platformio.org/en/latest/what-is-platformio.html?utm_source=arduino-esp8266>`__
+- `PlatformIO IDE <https://platformio.org/platformio-ide?utm_source=arduino-esp8266>`__
+- `PlatformIO Core <https://docs.platformio.org/en/latest/core.html?utm_source=arduino-esp8266>`__ (command line tool)
+- `Advanced usage <https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=arduino-esp8266>`__ - custom settings, uploading to SPIFFS, Over-the-Air (OTA), staging version
+- `Integration with Cloud and Standalone IDEs <https://docs.platformio.org/en/latest/ide.html?utm_source=arduino-esp8266>`__ - Cloud9, Codeanywhere, Eclipse Che (Codenvy), Atom, CLion, Eclipse, Emacs, NetBeans, Qt Creator, Sublime Text, VIM, Visual Studio, and VSCode
+- `Project Examples <https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=arduino-esp8266#examples>`__
diff --git a/libraries/ArduinoOTA/ArduinoOTA.cpp b/libraries/ArduinoOTA/ArduinoOTA.cpp
index 0b0789474..64e8397a2 100644
--- a/libraries/ArduinoOTA/ArduinoOTA.cpp
+++ b/libraries/ArduinoOTA/ArduinoOTA.cpp
@@ -328,9 +328,13 @@ void ArduinoOTAClass::_runUpdate() {
   }
 
   if (Update.end()) {
-    client.print("OK");
-    client.stop();
+    // Ensure last count packet has been sent out and not combined with the final OK
+    client.flush();
     delay(1000);
+    client.print("OK");
+    client.flush();
+    delay(1000);
+    client.stop();
 #ifdef OTA_DEBUG
     OTA_DEBUG.printf("Update Success\n");
 #endif
diff --git a/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp b/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp
index ff46822c3..5212dcf3e 100644
--- a/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp
+++ b/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp
@@ -423,7 +423,6 @@ void HTTPClient::end(void)
 {
     disconnect(false);
     clear();
-    _redirectCount = 0;
 }
 
 /**
@@ -558,8 +557,17 @@ bool HTTPClient::setURL(const String& url)
 /**
  * set true to follow redirects.
  * @param follow
+ * @deprecated
  */
 void HTTPClient::setFollowRedirects(bool follow)
+{
+    _followRedirects = follow ? HTTPC_STRICT_FOLLOW_REDIRECTS : HTTPC_DISABLE_FOLLOW_REDIRECTS;
+}
+/**
+ * set redirect follow mode. See `followRedirects_t` enum for avaliable modes.
+ * @param follow
+ */
+void HTTPClient::setFollowRedirects(followRedirects_t follow)
 {
     _followRedirects = follow;
 }
@@ -652,8 +660,9 @@ int HTTPClient::sendRequest(const char * type, const String& payload)
  */
 int HTTPClient::sendRequest(const char * type, const uint8_t * payload, size_t size)
 {
+    int code;
     bool redirect = false;
-    int code = 0;
+    uint16_t redirectCount = 0;
     do {
         // wipe out any existing headers from previous request
         for(size_t i = 0; i < _headerKeysCount; i++) {
@@ -662,8 +671,7 @@ int HTTPClient::sendRequest(const char * type, const uint8_t * payload, size_t s
             }
         }
 
-        redirect = false;
-        DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] type: '%s' redirCount: %d\n", type, _redirectCount);
+        DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] type: '%s' redirCount: %d\n", type, redirectCount);
 
         // connect to server
         if(!connect()) {
@@ -687,9 +695,9 @@ int HTTPClient::sendRequest(const char * type, const uint8_t * payload, size_t s
                 int towrite = std::min((int)size, (int)HTTP_TCP_BUFFER_SIZE);
                 written = _client->write(p + bytesWritten, towrite);
                 if (written < 0) {
-                     return returnError(HTTPC_ERROR_SEND_PAYLOAD_FAILED);
+                        return returnError(HTTPC_ERROR_SEND_PAYLOAD_FAILED);
                 } else if (written == 0) {
-                     return returnError(HTTPC_ERROR_CONNECTION_LOST);
+                        return returnError(HTTPC_ERROR_CONNECTION_LOST);
                 }
                 bytesWritten += written;
                 size -= written;
@@ -700,42 +708,67 @@ int HTTPClient::sendRequest(const char * type, const uint8_t * payload, size_t s
         code = handleHeaderResponse();
 
         //
-        // We can follow redirects for 301/302/307 for GET and HEAD requests and
-        // and we have not exceeded the redirect limit preventing an infinite
-        // redirect loop.
-        //
+        // Handle redirections as stated in RFC document:
         // https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
         //
-        if (_followRedirects &&
-                (_redirectCount < _redirectLimit) &&
-                (_location.length() > 0) &&
-                (code == 301 || code == 302 || code == 307) &&
-                (!strcmp(type, "GET") || !strcmp(type, "HEAD"))
-                ) {
-            _redirectCount += 1; // increment the count for redirect.
-            redirect = true;
-            DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] following redirect:: '%s' redirCount: %d\n", _location.c_str(), _redirectCount);
-            if (!setURL(_location)) {
-                // return the redirect instead of handling on failure of setURL()
-                redirect = false;
+        // Implementing HTTP_CODE_FOUND as redirection with GET method,
+        // to follow most of existing user agent implementations.
+        //
+        redirect = false;
+        if (
+            _followRedirects != HTTPC_DISABLE_FOLLOW_REDIRECTS && 
+            redirectCount < _redirectLimit &&
+            _location.length() > 0
+        ) {
+            switch (code) {
+                // redirecting using the same method
+                case HTTP_CODE_MOVED_PERMANENTLY:
+                case HTTP_CODE_TEMPORARY_REDIRECT: {
+                    if (
+                        // allow to force redirections on other methods
+                        // (the RFC require user to accept the redirection)
+                        _followRedirects == HTTPC_FORCE_FOLLOW_REDIRECTS ||
+                        // allow GET and HEAD methods without force
+                        !strcmp(type, "GET") || 
+                        !strcmp(type, "HEAD")
+                    ) {
+                        redirectCount += 1;
+                        DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] following redirect (the same method): '%s' redirCount: %d\n", _location.c_str(), redirectCount);
+                        if (!setURL(_location)) {
+                            DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] failed setting URL for redirection\n");
+                            // no redirection
+                            break;
+                        }
+                        // redirect using the same request method and payload, diffrent URL
+                        redirect = true;
+                    }
+                    break;
+                }
+                // redirecting with method dropped to GET or HEAD
+                // note: it does not need `HTTPC_FORCE_FOLLOW_REDIRECTS` for any method
+                case HTTP_CODE_FOUND:
+                case HTTP_CODE_SEE_OTHER: {
+                    redirectCount += 1;
+                    DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] following redirect (dropped to GET/HEAD): '%s' redirCount: %d\n", _location.c_str(), redirectCount);
+                    if (!setURL(_location)) {
+                        DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] failed setting URL for redirection\n");
+                        // no redirection
+                        break;
+                    }
+                    // redirect after changing method to GET/HEAD and dropping payload
+                    type = "GET";
+                    payload = nullptr;
+                    size = 0;
+                    redirect = true;
+                    break;
+                }
+
+                default:
+                    break;
             }
         }
-
     } while (redirect);
 
-    // handle 303 redirect for non GET/HEAD by changing to GET and requesting new url
-    if (_followRedirects &&
-            (_redirectCount < _redirectLimit) &&
-            (_location.length() > 0) &&
-            (code == 303) &&
-            strcmp(type, "GET") && strcmp(type, "HEAD")
-            ) {
-        _redirectCount += 1;
-        if (setURL(_location)) {
-            code = sendRequest("GET");
-        }
-    }
-
     // handle Server Response (Header)
     return returnError(code);
 }
diff --git a/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h b/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h
index 1d7548f0f..1ab26c8de 100644
--- a/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h
+++ b/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h
@@ -130,6 +130,23 @@ typedef enum {
     HTTPC_TE_CHUNKED
 } transferEncoding_t;
 
+/**
+ * redirection follow mode.
+ * + `HTTPC_DISABLE_FOLLOW_REDIRECTS` - no redirection will be followed.
+ * + `HTTPC_STRICT_FOLLOW_REDIRECTS` - strict RFC2616, only requests using
+ *      GET or HEAD methods will be redirected (using the same method),
+ *      since the RFC requires end-user confirmation in other cases.
+ * + `HTTPC_FORCE_FOLLOW_REDIRECTS` - all redirections will be followed,
+ *      regardless of a used method. New request will use the same method,
+ *      and they will include the same body data and the same headers.
+ *      In the sense of the RFC, it's just like every redirection is confirmed.
+ */
+typedef enum {
+    HTTPC_DISABLE_FOLLOW_REDIRECTS,
+    HTTPC_STRICT_FOLLOW_REDIRECTS,
+    HTTPC_FORCE_FOLLOW_REDIRECTS
+} followRedirects_t;
+
 #if HTTPCLIENT_1_1_COMPATIBLE
 class TransportTraits;
 typedef std::unique_ptr<TransportTraits> TransportTraitsPtr;
@@ -173,8 +190,12 @@ public:
     void setAuthorization(const char * user, const char * password);
     void setAuthorization(const char * auth);
     void setTimeout(uint16_t timeout);
-    void setFollowRedirects(bool follow);
+
+    // Redirections
+    void setFollowRedirects(bool follow) __attribute__ ((deprecated));
+    void setFollowRedirects(followRedirects_t follow);
     void setRedirectLimit(uint16_t limit); // max redirects to follow for a single request
+
     bool setURL(const String& url); // handy for handling redirects
     void useHTTP10(bool usehttp10 = true);
 
@@ -252,8 +273,7 @@ protected:
     int _returnCode = 0;
     int _size = -1;
     bool _canReuse = false;
-    bool _followRedirects = false;
-    uint16_t _redirectCount = 0;
+    followRedirects_t _followRedirects = HTTPC_DISABLE_FOLLOW_REDIRECTS;
     uint16_t _redirectLimit = 10;
     String _location;
     transferEncoding_t _transferEncoding = HTTPC_TE_IDENTITY;
diff --git a/libraries/ESP8266WebServer/examples/FSBrowser/FSBrowser.ino b/libraries/ESP8266WebServer/examples/FSBrowser/FSBrowser.ino
index fb5847d4b..bd25fad58 100644
--- a/libraries/ESP8266WebServer/examples/FSBrowser/FSBrowser.ino
+++ b/libraries/ESP8266WebServer/examples/FSBrowser/FSBrowser.ino
@@ -186,12 +186,27 @@ void handleFileList() {
   Dir dir = filesystem->openDir(path);
   path.clear();
 
-  String output = "[";
+  // use HTTP/1.1 Chunked response to avoid building a huge temporary string
+  if (!server.chunkedResponseModeStart(200, "text/json")) {
+    server.send(505, FPSTR("text/html"), FPSTR("HTTP1.1 required"));
+    return;
+  }
+
+  // use the same string for every line
+  String output;
+  output.reserve(64);
   while (dir.next()) {
-    File entry = dir.openFile("r");
-    if (output != "[") {
-      output += ',';
+
+    if (output.length()) {
+      // send string from previous iteration
+      // as an HTTP chunk
+      server.sendContent(output);
+      output = ',';
+    } else {
+      output = '[';
     }
+
+    File entry = dir.openFile("r");
     bool isDir = false;
     output += "{\"type\":\"";
     output += (isDir) ? "dir" : "file";
@@ -205,8 +220,10 @@ void handleFileList() {
     entry.close();
   }
 
+  // send last string
   output += "]";
-  server.send(200, "text/json", output);
+  server.sendContent(output);
+  server.chunkedResponseFinalize();
 }
 
 void setup(void) {
diff --git a/libraries/ESP8266WebServer/src/ESP8266WebServer.h b/libraries/ESP8266WebServer/src/ESP8266WebServer.h
index eefcba2ba..9e999acad 100644
--- a/libraries/ESP8266WebServer/src/ESP8266WebServer.h
+++ b/libraries/ESP8266WebServer/src/ESP8266WebServer.h
@@ -149,18 +149,36 @@ public:
   void sendContent(const char *content) { sendContent_P(content); }
   void sendContent(const char *content, size_t size) { sendContent_P(content, size); }
 
+  bool chunkedResponseModeStart_P (int code, PGM_P content_type) {
+    if (_currentVersion == 0)
+        // no chunk mode in HTTP/1.0
+        return false;
+    setContentLength(CONTENT_LENGTH_UNKNOWN);
+    send_P(code, content_type, "");
+    return true;
+  }
+  bool chunkedResponseModeStart (int code, const char* content_type) {
+    return chunkedResponseModeStart_P(code, content_type);
+  }
+  bool chunkedResponseModeStart (int code, const String& content_type) {
+    return chunkedResponseModeStart_P(code, content_type.c_str());
+  }
+  void chunkedResponseFinalize () {
+    sendContent(emptyString);
+  }
+
   static String credentialHash(const String& username, const String& realm, const String& password);
 
   static String urlDecode(const String& text);
 
-  // Handle a GET request by sending a response header and stream file content to response body 
+  // Handle a GET request by sending a response header and stream file content to response body
   template<typename T>
   size_t streamFile(T &file, const String& contentType) {
     return streamFile(file, contentType, HTTP_GET);
   }
 
   // Implement GET and HEAD requests for files.
-  // Stream body on HTTP_GET but not on HTTP_HEAD requests. 
+  // Stream body on HTTP_GET but not on HTTP_HEAD requests.
   template<typename T>
   size_t streamFile(T &file, const String& contentType, HTTPMethod requestMethod) {
     size_t contentLength = 0;
diff --git a/libraries/ESP8266WiFi/examples/IPv6/IPv6.ino b/libraries/ESP8266WiFi/examples/IPv6/IPv6.ino
index 1c7b1c081..48bd5a449 100644
--- a/libraries/ESP8266WiFi/examples/IPv6/IPv6.ino
+++ b/libraries/ESP8266WiFi/examples/IPv6/IPv6.ino
@@ -1,4 +1,3 @@
-
 /*
   arduino IPv6 example
   released to public domain
@@ -27,7 +26,8 @@
 #define STAPSK  "your-password"
 #endif
 
-#define FQDN  F("www.google.com") // with both IPv4 & IPv6 addresses
+#define FQDN  F("www.google.com")  // with both IPv4 & IPv6 addresses
+#define FQDN2 F("www.yahoo.com")   // with both IPv4 & IPv6 addresses
 #define FQDN6 F("ipv6.google.com") // does not resolve in IPv4
 #define STATUSDELAY_MS 10000
 #define TCP_PORT 23
@@ -50,6 +50,21 @@ void fqdn(Print& out, const String& fqdn) {
   }
 }
 
+#if LWIP_IPV4 && LWIP_IPV6
+void fqdn_rt(Print& out, const String& fqdn, DNSResolveType resolveType) {
+  out.print(F("resolving "));
+  out.print(fqdn);
+  out.print(F(": "));
+  IPAddress result;
+  if (WiFi.hostByName(fqdn.c_str(), result, 10000, resolveType)) {
+    result.printTo(out);
+    out.println();
+  } else {
+    out.println(F("timeout or not found"));
+  }
+}
+#endif
+
 void status(Print& out) {
   out.println(F("------------------------------"));
   out.println(ESP.getFullVersion());
@@ -85,7 +100,10 @@ void status(Print& out) {
   // an example is provided with a fqdn which does not resolve with IPv4
   fqdn(out, FQDN);
   fqdn(out, FQDN6);
-
+#if LWIP_IPV4 && LWIP_IPV6
+  fqdn_rt(out, FQDN,  DNSResolveType::DNS_AddrType_IPv4_IPv6); // IPv4 before IPv6
+  fqdn_rt(out, FQDN2, DNSResolveType::DNS_AddrType_IPv6_IPv4); // IPv6 before IPv4
+#endif
   out.println(F("------------------------------"));
 }
 
diff --git a/libraries/ESP8266WiFi/keywords.txt b/libraries/ESP8266WiFi/keywords.txt
index b24bfc598..16eea2422 100644
--- a/libraries/ESP8266WiFi/keywords.txt
+++ b/libraries/ESP8266WiFi/keywords.txt
@@ -26,6 +26,7 @@ PublicKey	KEYWORD1
 CertStoreSPIFFSBearSSL	KEYWORD1
 CertStoreSDBearSSL	KEYWORD1
 Session	KEYWORD1
+ESP8266WiFiGratuitous	KEYWORD1
 
 
 #######################################
@@ -108,6 +109,9 @@ psk	KEYWORD2
 BSSID	KEYWORD2
 BSSIDstr	KEYWORD2
 RSSI	KEYWORD2
+stationKeepAliveSetIntervalMs	KEYWORD2
+stationKeepAliveStop	KEYWORD2
+stationKeepAliveNow	KEYWORD2
 enableInsecureWEP	KEYWORD2
 getListenInterval	KEYWORD2
 isSleepLevelMax		KEYWORD2
diff --git a/libraries/ESP8266WiFi/src/BearSSLHelpers.cpp b/libraries/ESP8266WiFi/src/BearSSLHelpers.cpp
index ffce2b00e..f96254779 100644
--- a/libraries/ESP8266WiFi/src/BearSSLHelpers.cpp
+++ b/libraries/ESP8266WiFi/src/BearSSLHelpers.cpp
@@ -870,9 +870,9 @@ uint32_t SigningVerifier::length()
   }
 }
 
-bool SigningVerifier::verify(UpdaterHashClass *hash, const void *signature, uint32_t signatureLen) {
-  if (!_pubKey || !hash || !signature || signatureLen != length()) return false;
-
+// We need to use the 2nd stack to do a verification, so do the thunk
+// directly inside the class function for ease of use.
+extern "C" bool SigningVerifier_verify(PublicKey *_pubKey, UpdaterHashClass *hash, const void *signature, uint32_t signatureLen) {
   if (_pubKey->isRSA()) {
     bool ret;
     unsigned char vrf[hash->len()];
@@ -890,6 +890,20 @@ bool SigningVerifier::verify(UpdaterHashClass *hash, const void *signature, uint
   }
 };
 
+#if !CORE_MOCK
+make_stack_thunk(SigningVerifier_verify);
+extern "C" bool thunk_SigningVerifier_verify(PublicKey *_pubKey, UpdaterHashClass *hash, const void *signature, uint32_t signatureLen);
+#endif
+
+bool SigningVerifier::verify(UpdaterHashClass *hash, const void *signature, uint32_t signatureLen) {
+  if (!_pubKey || !hash || !signature || signatureLen != length()) return false;
+#if !CORE_MOCK
+    return thunk_SigningVerifier_verify(_pubKey, hash, signature, signatureLen);
+#else
+    return SigningVerifier_verify(_pubKey, hash, signature, signatureLen);
+#endif
+}
+
 #if !CORE_MOCK
 
 // Second stack thunked helpers
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.cpp b/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.cpp
index 4b2eb54ce..41d771fb6 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.cpp
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.cpp
@@ -608,7 +608,7 @@ int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResul
 int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms)
 {
     ip_addr_t addr;
-    aResult = static_cast<uint32_t>(0);
+    aResult = static_cast<uint32_t>(INADDR_NONE);
 
     if(aResult.fromString(aHostname)) {
         // Host name is a IP address use it!
@@ -617,7 +617,11 @@ int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResul
     }
 
     DEBUG_WIFI_GENERIC("[hostByName] request IP for: %s\n", aHostname);
+#if LWIP_IPV4 && LWIP_IPV6
+    err_t err = dns_gethostbyname_addrtype(aHostname, &addr, &wifi_dns_found_callback, &aResult,LWIP_DNS_ADDRTYPE_DEFAULT);
+#else
     err_t err = dns_gethostbyname(aHostname, &addr, &wifi_dns_found_callback, &aResult);
+#endif
     if(err == ERR_OK) {
         aResult = IPAddress(&addr);
     } else if(err == ERR_INPROGRESS) {
@@ -640,6 +644,57 @@ int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResul
     return (err == ERR_OK) ? 1 : 0;
 }
 
+#if LWIP_IPV4 && LWIP_IPV6
+int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms, DNSResolveType resolveType)
+{
+    ip_addr_t addr;
+    err_t err;
+    aResult = static_cast<uint32_t>(INADDR_NONE);
+
+    if(aResult.fromString(aHostname)) {
+        // Host name is a IP address use it!
+        DEBUG_WIFI_GENERIC("[hostByName] Host: %s is a IP!\n", aHostname);
+        return 1;
+    }
+
+    DEBUG_WIFI_GENERIC("[hostByName] request IP for: %s\n", aHostname);
+    switch(resolveType)
+    {
+      // Use selected addrtype
+      case DNSResolveType::DNS_AddrType_IPv4:
+      case DNSResolveType::DNS_AddrType_IPv6:
+      case DNSResolveType::DNS_AddrType_IPv4_IPv6:
+      case DNSResolveType::DNS_AddrType_IPv6_IPv4:
+         err = dns_gethostbyname_addrtype(aHostname, &addr, &wifi_dns_found_callback, &aResult, (uint8_t) resolveType);
+	 break;
+      default:
+         err = dns_gethostbyname_addrtype(aHostname, &addr, &wifi_dns_found_callback, &aResult, LWIP_DNS_ADDRTYPE_DEFAULT); // If illegal type, use default.
+	 break;
+    }
+
+    if(err == ERR_OK) {
+        aResult = IPAddress(&addr);
+    } else if(err == ERR_INPROGRESS) {
+        _dns_lookup_pending = true;
+        delay(timeout_ms);
+        // will resume on timeout or when wifi_dns_found_callback fires
+        _dns_lookup_pending = false;
+        // will return here when dns_found_callback fires
+        if(aResult.isSet()) {
+            err = ERR_OK;
+        }
+    }
+
+    if(err != 0) {
+        DEBUG_WIFI_GENERIC("[hostByName] Host: %s lookup error: %d!\n", aHostname, (int)err);
+    } else {
+        DEBUG_WIFI_GENERIC("[hostByName] Host: %s IP: %s\n", aHostname, aResult.toString().c_str());
+    }
+
+    return (err == ERR_OK) ? 1 : 0;
+}
+#endif
+
 /**
  * DNS callback
  * @param name
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.h b/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.h
index 1f5ec5c99..b5f307aed 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.h
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.h
@@ -42,6 +42,14 @@ typedef std::shared_ptr<WiFiEventHandlerOpaque> WiFiEventHandler;
 
 typedef void (*WiFiEventCb)(WiFiEvent_t);
 
+enum class DNSResolveType: uint8_t
+{
+    DNS_AddrType_IPv4 = 0,	// LWIP_DNS_ADDRTYPE_IPV4 = 0
+    DNS_AddrType_IPv6,		// LWIP_DNS_ADDRTYPE_IPV6 = 1
+    DNS_AddrType_IPv4_IPv6,	// LWIP_DNS_ADDRTYPE_IPV4_IPV6 = 2
+    DNS_AddrType_IPv6_IPv4	// LWIP_DNS_ADDRTYPE_IPV6_IPV4 = 3
+};
+
 struct WiFiState;
 
 class ESP8266WiFiGenericClass {
@@ -113,6 +121,9 @@ class ESP8266WiFiGenericClass {
     public:
         int hostByName(const char* aHostname, IPAddress& aResult);
         int hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms);
+#if LWIP_IPV4 && LWIP_IPV6
+        int hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms, DNSResolveType resolveType);
+#endif
         bool getPersistent();
 
     protected:
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiGratuitous.cpp b/libraries/ESP8266WiFi/src/ESP8266WiFiGratuitous.cpp
new file mode 100644
index 000000000..1ba3f862b
--- /dev/null
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiGratuitous.cpp
@@ -0,0 +1,95 @@
+/*
+ ESP8266WiFiGratuitous.cpp - esp8266 Wifi support
+ copyright esp8266/arduino
+
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+extern "C"
+{
+#include "lwip/init.h" // LWIP_VERSION_*
+#if LWIP_VERSION_MAJOR == 1
+#include "netif/wlan_lwip_if.h" // eagle_lwip_getif()
+#include "netif/etharp.h" // gratuitous arp
+#include "user_interface.h"
+#else
+#include "lwip/etharp.h" // gratuitous arp
+#endif
+} // extern "C"
+
+#include <Schedule.h>
+
+#include "ESP8266WiFiGratuitous.h"
+
+namespace experimental
+{
+
+ETSTimer* ESP8266WiFiGratuitous::_timer = nullptr;
+
+void ESP8266WiFiGratuitous::stationKeepAliveNow ()
+{
+    for (netif* interface = netif_list; interface != nullptr; interface = interface->next)
+        if (
+               (interface->flags & NETIF_FLAG_LINK_UP)
+            && (interface->flags & NETIF_FLAG_UP)
+#if LWIP_VERSION_MAJOR == 1
+            && interface == eagle_lwip_getif(STATION_IF) /* lwip1 does not set if->num properly */
+            && (!ip_addr_isany(&interface->ip_addr))
+#else
+            && interface->num == STATION_IF
+            && (!ip4_addr_isany_val(*netif_ip4_addr(interface)))
+#endif
+        )
+        {
+            etharp_gratuitous(interface);
+            break;
+        }
+}
+
+void ESP8266WiFiGratuitous::scheduleItForNextYieldOnce (void*)
+{
+    schedule_recurrent_function_us([]()
+    {
+        ESP8266WiFiGratuitous::stationKeepAliveNow();
+        return false;
+    }, 0);
+}
+
+bool ESP8266WiFiGratuitous::stationKeepAliveSetIntervalMs (uint32_t ms)
+{
+    if (_timer)
+    {
+        os_timer_disarm(_timer);
+        free(_timer);
+        _timer = nullptr;
+    }
+
+    if (ms)
+    {
+        // send one now
+        stationKeepAliveNow();
+
+        _timer = (ETSTimer*)malloc(sizeof(ETSTimer));
+        if (_timer == nullptr)
+            return false;
+
+        os_timer_setfn(_timer, ESP8266WiFiGratuitous::scheduleItForNextYieldOnce, nullptr);
+        os_timer_arm(_timer, ms, true);
+    }
+
+    return true;
+}
+
+}; // experimental::
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiGratuitous.h b/libraries/ESP8266WiFi/src/ESP8266WiFiGratuitous.h
new file mode 100644
index 000000000..d86426cd8
--- /dev/null
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiGratuitous.h
@@ -0,0 +1,54 @@
+/*
+ ESP8266WiFiGratuitous.h - esp8266 Wifi support
+ copyright esp8266/arduino
+
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef ESP8266WIFIGRATUITOUS_H_
+#define ESP8266WIFIGRATUITOUS_H_
+
+#include <stdint.h>  // uint32_t
+#include <ets_sys.h> // ETSTimer
+
+namespace experimental
+{
+
+class ESP8266WiFiGratuitous
+{
+public:
+
+    // disable(0) or enable/update automatic sending of Gratuitous ARP packets.
+    // A gratuitous ARP packet is immediately sent when calling this function, then
+    // based on a time interval in milliseconds, default = 1s
+    // return value: true when started, false otherwise
+    static bool stationKeepAliveSetIntervalMs (uint32_t ms = 1000);
+
+    // request for stopping arp gratuitous packets
+    static void stationKeepAliveStop () { (void)stationKeepAliveSetIntervalMs(0); }
+
+    // immediately send one gratuitous ARP from STA
+    static void stationKeepAliveNow ();
+
+protected:
+
+    static void scheduleItForNextYieldOnce (void*);
+
+    static ETSTimer* _timer;
+};
+
+}; // experimental::
+
+#endif // ESP8266WIFIGRATUITOUS_H_
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.cpp b/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.cpp
index 8f52942b7..26fb4b9d3 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.cpp
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.cpp
@@ -89,7 +89,7 @@ static bool sta_config_equal(const station_config& lhs, const station_config& rh
             return false;
         }
     }
-    
+
     if(lhs.threshold.rssi != rhs.threshold.rssi) {
         return false;
     }
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h b/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h
index 696ff1b39..cf38e1254 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h
@@ -41,8 +41,8 @@ class ESP8266WiFiSTAClass {
         wl_status_t begin(const String& ssid, const String& passphrase = emptyString, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
         wl_status_t begin();
 
-        //The argument order for ESP is not the same as for Arduino. However, there is compatibility code under the hood 
-        //to detect Arduino arg order, and handle it correctly. Be aware that the Arduino default value handling doesn't 
+        //The argument order for ESP is not the same as for Arduino. However, there is compatibility code under the hood
+        //to detect Arduino arg order, and handle it correctly. Be aware that the Arduino default value handling doesn't
         //work here (see Arduino docs for gway/subnet defaults). In other words: at least 3 args must always be given.
         bool config(IPAddress local_ip, IPAddress gateway, IPAddress subnet, IPAddress dns1 = (uint32_t)0x00000000, IPAddress dns2 = (uint32_t)0x00000000);
 
diff --git a/libraries/ESP8266WiFi/src/include/ClientContext.h b/libraries/ESP8266WiFi/src/include/ClientContext.h
index 6ce97115f..8095e402a 100644
--- a/libraries/ESP8266WiFi/src/include/ClientContext.h
+++ b/libraries/ESP8266WiFi/src/include/ClientContext.h
@@ -127,8 +127,14 @@ public:
         }
     }
 
-    int connect(CONST ip_addr_t* addr, uint16_t port)
+    int connect(ip_addr_t* addr, uint16_t port)
     {
+#if LWIP_IPV6
+        // Set zone so that link local addresses use the default interface
+        if (IP_IS_V6(addr) && ip6_addr_lacks_zone(ip_2_ip6(addr), IP6_UNKNOWN)) {
+            ip6_addr_assign_zone(ip_2_ip6(addr), IP6_UNKNOWN, netif_default);
+        }
+#endif
         err_t err = tcp_connect(_pcb, addr, port, &ClientContext::_s_connected);
         if (err != ERR_OK) {
             return 0;
diff --git a/libraries/ESP8266WiFi/src/include/UdpContext.h b/libraries/ESP8266WiFi/src/include/UdpContext.h
index 8534c61f1..a81384b2a 100644
--- a/libraries/ESP8266WiFi/src/include/UdpContext.h
+++ b/libraries/ESP8266WiFi/src/include/UdpContext.h
@@ -114,6 +114,12 @@ public:
     {
         _pcb->remote_ip = addr;
         _pcb->remote_port = port;
+#if LWIP_IPV6
+        // Set zone so that link local addresses use the default interface
+        if (IP_IS_V6(&_pcb->remote_ip) && ip6_addr_lacks_zone(ip_2_ip6(&_pcb->remote_ip), IP6_UNKNOWN)) {
+            ip6_addr_assign_zone(ip_2_ip6(&_pcb->remote_ip), IP6_UNKNOWN, netif_default);
+        }
+#endif
         return true;
     }
 
diff --git a/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.cpp b/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.cpp
index 9d56718c1..a7fe1934d 100755
--- a/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.cpp
+++ b/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.cpp
@@ -30,12 +30,12 @@ extern "C" uint32_t _FS_start;
 extern "C" uint32_t _FS_end;
 
 ESP8266HTTPUpdate::ESP8266HTTPUpdate(void)
-        : _httpClientTimeout(8000), _followRedirects(false), _ledPin(-1)
+        : _httpClientTimeout(8000), _followRedirects(HTTPC_DISABLE_FOLLOW_REDIRECTS), _ledPin(-1)
 {
 }
 
 ESP8266HTTPUpdate::ESP8266HTTPUpdate(int httpClientTimeout)
-        : _httpClientTimeout(httpClientTimeout), _followRedirects(false), _ledPin(-1)
+        : _httpClientTimeout(httpClientTimeout), _followRedirects(HTTPC_DISABLE_FOLLOW_REDIRECTS), _ledPin(-1)
 {
 }
 
diff --git a/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.h b/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.h
index 8d06def9d..ddbd307ad 100755
--- a/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.h
+++ b/libraries/ESP8266httpUpdate/src/ESP8266httpUpdate.h
@@ -82,7 +82,20 @@ public:
         _rebootOnUpdate = reboot;
     }
 
-    void followRedirects(bool follow)
+    /**
+     * set true to follow redirects.
+     * @param follow
+     * @deprecated Please use `setFollowRedirects(followRedirects_t follow)`
+      */
+    void followRedirects(bool follow) __attribute__ ((deprecated))
+    {
+        _followRedirects = follow ? HTTPC_STRICT_FOLLOW_REDIRECTS : HTTPC_DISABLE_FOLLOW_REDIRECTS;
+    }
+    /**
+      * set redirect follow mode. See `followRedirects_t` enum for avaliable modes.
+      * @param follow
+      */
+    void setFollowRedirects(followRedirects_t follow)
     {
         _followRedirects = follow;
     }
@@ -160,7 +173,7 @@ protected:
     bool _closeConnectionsOnUpdate = true;
 private:
     int _httpClientTimeout;
-    bool _followRedirects;
+    followRedirects_t _followRedirects;
 
     // Callbacks
     HTTPUpdateStartCB    _cbStart;
diff --git a/libraries/ESP8266mDNS/src/LEAmDNS.cpp b/libraries/ESP8266mDNS/src/LEAmDNS.cpp
index 628432411..87ff5167f 100644
--- a/libraries/ESP8266mDNS/src/LEAmDNS.cpp
+++ b/libraries/ESP8266mDNS/src/LEAmDNS.cpp
@@ -767,6 +767,12 @@ uint32_t MDNSResponder::queryService(const char* p_pcService,
                                      const char* p_pcProtocol,
                                      const uint16_t p_u16Timeout /*= MDNS_QUERYSERVICES_WAIT_TIME*/)
 {
+    if (0 == m_pUDPContext)
+    {
+        // safeguard against misuse
+        return 0;
+    }
+
     DEBUG_EX_INFO(DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] queryService '%s.%s'\n"), p_pcService, p_pcProtocol););
 
     uint32_t    u32Result = 0;
diff --git a/libraries/SoftwareSerial b/libraries/SoftwareSerial
index 94b2388a4..91ea6b1b1 160000
--- a/libraries/SoftwareSerial
+++ b/libraries/SoftwareSerial
@@ -1 +1 @@
-Subproject commit 94b2388a4752f2b165371313f4d942daebff6eee
+Subproject commit 91ea6b1b1c34601565b23c96c4441f2d399a4f99
diff --git a/libraries/Ticker/src/Ticker.h b/libraries/Ticker/src/Ticker.h
index 436a68ce8..07ce33c62 100644
--- a/libraries/Ticker/src/Ticker.h
+++ b/libraries/Ticker/src/Ticker.h
@@ -35,30 +35,42 @@ public:
     typedef void (*callback_with_arg_t)(void*);
     typedef std::function<void(void)> callback_function_t;
 
+    // callback will be called at following loop() after ticker fires
     void attach_scheduled(float seconds, callback_function_t callback)
     {
         _callback_function = [callback]() { schedule_function(callback); };
         _attach_ms(1000UL * seconds, true);
     }
 
+    // callback will be called in SYS ctx when ticker fires
     void attach(float seconds, callback_function_t callback)
     {
         _callback_function = std::move(callback);
         _attach_ms(1000UL * seconds, true);
     }
 
+    // callback will be called at following loop() after ticker fires
     void attach_ms_scheduled(uint32_t milliseconds, callback_function_t callback)
     {
         _callback_function = [callback]() { schedule_function(callback); };
         _attach_ms(milliseconds, true);
     }
 
+    // callback will be called at following yield() after ticker fires
+    void attach_ms_scheduled_accurate(uint32_t milliseconds, callback_function_t callback)
+    {
+        _callback_function = [callback]() { schedule_recurrent_function_us([callback]() { callback(); return false; }, 0); };
+        _attach_ms(milliseconds, true);
+    }
+
+    // callback will be called in SYS ctx when ticker fires
     void attach_ms(uint32_t milliseconds, callback_function_t callback)
     {
         _callback_function = std::move(callback);
         _attach_ms(milliseconds, true);
     }
 
+    // callback will be called in SYS ctx when ticker fires
     template<typename TArg>
     void attach(float seconds, void (*callback)(TArg), TArg arg)
     {
@@ -66,6 +78,7 @@ public:
         _attach_ms(1000UL * seconds, true, reinterpret_cast<callback_with_arg_t>(callback), reinterpret_cast<void*>(arg));
     }
 
+    // callback will be called in SYS ctx when ticker fires
     template<typename TArg>
     void attach_ms(uint32_t milliseconds, void (*callback)(TArg), TArg arg)
     {
@@ -73,30 +86,35 @@ public:
         _attach_ms(milliseconds, true, reinterpret_cast<callback_with_arg_t>(callback), reinterpret_cast<void*>(arg));
     }
 
+    // callback will be called at following loop() after ticker fires
     void once_scheduled(float seconds, callback_function_t callback)
     {
         _callback_function = [callback]() { schedule_function(callback); };
         _attach_ms(1000UL * seconds, false);
     }
 
+    // callback will be called in SYS ctx when ticker fires
     void once(float seconds, callback_function_t callback)
     {
         _callback_function = std::move(callback);
         _attach_ms(1000UL * seconds, false);
     }
 
+    // callback will be called at following loop() after ticker fires
     void once_ms_scheduled(uint32_t milliseconds, callback_function_t callback)
     {
         _callback_function = [callback]() { schedule_function(callback); };
         _attach_ms(milliseconds, false);
     }
 
+    // callback will be called in SYS ctx when ticker fires
     void once_ms(uint32_t milliseconds, callback_function_t callback)
     {
         _callback_function = std::move(callback);
         _attach_ms(milliseconds, false);
     }
 
+    // callback will be called in SYS ctx when ticker fires
     template<typename TArg>
     void once(float seconds, void (*callback)(TArg), TArg arg)
     {
@@ -104,6 +122,7 @@ public:
         _attach_ms(1000UL * seconds, false, reinterpret_cast<callback_with_arg_t>(callback), reinterpret_cast<void*>(arg));
     }
 
+    // callback will be called in SYS ctx when ticker fires
     template<typename TArg>
     void once_ms(uint32_t milliseconds, void (*callback)(TArg), TArg arg)
     {
diff --git a/libraries/esp8266/examples/NTP-TZ-DST/NTP-TZ-DST.ino b/libraries/esp8266/examples/NTP-TZ-DST/NTP-TZ-DST.ino
index 33cd14603..3a16efb61 100644
--- a/libraries/esp8266/examples/NTP-TZ-DST/NTP-TZ-DST.ino
+++ b/libraries/esp8266/examples/NTP-TZ-DST/NTP-TZ-DST.ino
@@ -134,7 +134,7 @@ void showTime() {
   Serial.println((uint32_t)now);
 
   // timezone and demo in the future
-  Serial.printf("timezone:  %s\n", getenv("TZ"));
+  Serial.printf("timezone:  %s\n", getenv("TZ") ? : "(none)");
 
   // human readable
   Serial.print("ctime:     ");
diff --git a/package/package_esp8266com_index.template.json b/package/package_esp8266com_index.template.json
index 86a9570bf..97a05e2bb 100644
--- a/package/package_esp8266com_index.template.json
+++ b/package/package_esp8266com_index.template.json
@@ -378,4 +378,4 @@
          ]
       }
    ]
-}
+}
\ No newline at end of file
diff --git a/tests/device/test_sw_http_client/test_sw_http_client.ino b/tests/device/test_sw_http_client/test_sw_http_client.ino
index 6de2314fa..3e60bf974 100644
--- a/tests/device/test_sw_http_client/test_sw_http_client.ino
+++ b/tests/device/test_sw_http_client/test_sw_http_client.ino
@@ -71,10 +71,10 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         http.end();
     }
     {
-        // 301 redirect with follow enabled
+        // GET 301 redirect with strict RFC follow enabled 
         WiFiClient client;
         HTTPClient http;
-        http.setFollowRedirects(true);
+        http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
         String uri = String("/redirect301?host=")+getenv("SERVER_IP");
         http.begin(client, getenv("SERVER_IP"), 8088, uri.c_str());
         auto httpCode = http.GET();
@@ -83,7 +83,7 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(payload == "redirect success");
     }
     {
-        // 301 redirect with follow disabled
+        // GET 301 redirect with follow disabled
         WiFiClient client;
         HTTPClient http;
         String uri = String("/redirect301?host=")+getenv("SERVER_IP");
@@ -92,10 +92,10 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(httpCode == 301);
     }
     {
-        // 302 redirect with follow enabled
+        // GET 302 redirect with strict RFC follow enabled 
         WiFiClient client;
         HTTPClient http;
-        http.setFollowRedirects(true);
+        http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
         String uri = String("/redirect302?host=")+getenv("SERVER_IP");
         http.begin(client, getenv("SERVER_IP"), 8088, uri.c_str());
         auto httpCode = http.GET();
@@ -104,7 +104,7 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(payload == "redirect success");
     }
     {
-        // 302 redirect with follow disabled
+        // GET 302 redirect with follow disabled
         WiFiClient client;
         HTTPClient http;
         String uri = String("/redirect302?host=")+getenv("SERVER_IP");
@@ -113,10 +113,10 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(httpCode == 302);
     }
     {
-        // 307 redirect with follow enabled
+        // GET 307 redirect with strict RFC follow enabled
         WiFiClient client;
         HTTPClient http;
-        http.setFollowRedirects(true);
+        http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
         String uri = String("/redirect307?host=")+getenv("SERVER_IP");
         http.begin(client, getenv("SERVER_IP"), 8088, uri.c_str());
         auto httpCode = http.GET();
@@ -125,7 +125,7 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(payload == "redirect success");
     }
     {
-        // 307 redirect with follow disabled
+        // GET 307 redirect with follow disabled
         WiFiClient client;
         HTTPClient http;
         String uri = String("/redirect307?host=")+getenv("SERVER_IP");
@@ -134,10 +134,10 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(httpCode == 307);
     }
     {
-        // 301 exceeding redirect limit
+        // GET 301 exceeding redirect limit
         WiFiClient client;
         HTTPClient http;
-        http.setFollowRedirects(true);
+        http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
         http.setRedirectLimit(0);
         String uri = String("/redirect301?host=")+getenv("SERVER_IP");
         http.begin(client, getenv("SERVER_IP"), 8088, uri.c_str());
@@ -145,20 +145,22 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         REQUIRE(httpCode == 301);
     }
     {
-        // POST 303 redirect with follow enabled
+        // POST 303 redirect with strict RFC follow enabled
         WiFiClient client;
         HTTPClient http;
-        http.setFollowRedirects(true);
+        http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
         http.begin(client, getenv("SERVER_IP"), 8088, "/redirect303");
         auto httpCode = http.POST(getenv("SERVER_IP"));
         REQUIRE(httpCode == HTTP_CODE_OK);
         String payload = http.getString();
         REQUIRE(payload == "redirect success");
+        // TODO: need check for dropping: redirection should use GET method
     }
     {
         // POST 303 redirect with follow disabled
         WiFiClient client;
         HTTPClient http;
+        http.setFollowRedirects(HTTPC_DISABLE_FOLLOW_REDIRECTS);
         http.begin(client, getenv("SERVER_IP"), 8088, "/redirect303");
         auto httpCode = http.POST(getenv("SERVER_IP"));
         REQUIRE(httpCode == 303);
@@ -167,6 +169,7 @@ TEST_CASE("HTTP GET & POST requests", "[HTTPClient]")
         // 302 redirect with follow disabled
         WiFiClient client;
         HTTPClient http;
+        http.setFollowRedirects(HTTPC_DISABLE_FOLLOW_REDIRECTS);
         String uri = String("/redirect302?host=")+getenv("SERVER_IP");
         http.begin(client, getenv("SERVER_IP"), 8088, uri.c_str());
         auto httpCode = http.GET();
diff --git a/tests/host/common/MockEsp.cpp b/tests/host/common/MockEsp.cpp
index c5ca502ed..0854bdcd7 100644
--- a/tests/host/common/MockEsp.cpp
+++ b/tests/host/common/MockEsp.cpp
@@ -118,11 +118,6 @@ uint32_t EspClass::getFreeSketchSpace()
   return 4 * 1024 * 1024;
 }
 
-uint8_t EspClass::getCpuFreqMHz()
-{
-  return F_CPU / 1000000;
-}
-
 const char *EspClass::getSdkVersion()
 {
   return "2.5.0";
diff --git a/tests/host/common/MocklwIP.cpp b/tests/host/common/MocklwIP.cpp
index bc5ae6ebc..f114572c1 100644
--- a/tests/host/common/MocklwIP.cpp
+++ b/tests/host/common/MocklwIP.cpp
@@ -26,4 +26,11 @@ const ip_addr_t* sntp_getserver(u8_t)
     return IP_ADDR_ANY;
 }
 
+err_t etharp_request(struct netif *netif, const ip4_addr_t *ipaddr)
+{
+    (void)netif;
+    (void)ipaddr;
+    return ERR_OK;
+}
+
 } // extern "C"
diff --git a/tests/platformio.sh b/tests/platformio.sh
index 4f1cbbb78..e2d24859d 100755
--- a/tests/platformio.sh
+++ b/tests/platformio.sh
@@ -7,8 +7,8 @@ source "$TRAVIS_BUILD_DIR"/tests/common.sh
 function install_platformio()
 {
     pip3 install --user -U https://github.com/platformio/platformio/archive/develop.zip
-    platformio platform install "https://github.com/platformio/platform-espressif8266.git#feature/stage"
-    sed -i 's/https:\/\/github\.com\/esp8266\/Arduino\.git/*/' ~/.platformio/platforms/espressif8266/platform.json
+    platformio platform install "https://github.com/platformio/platform-espressif8266.git"
+    python -c "import json; import os; fp=open(os.path.expanduser('~/.platformio/platforms/espressif8266/platform.json'), 'r+'); data=json.load(fp); data['packages']['framework-arduinoespressif8266']['version'] = '*'; fp.seek(0); fp.truncate(); json.dump(data, fp); fp.close()"
     ln -sf $TRAVIS_BUILD_DIR ~/.platformio/packages/framework-arduinoespressif8266
     # Install dependencies:
     # - esp8266/examples/ConfigFile
diff --git a/tools/boards.txt.py b/tools/boards.txt.py
index ff582896d..d33cbe1fc 100755
--- a/tools/boards.txt.py
+++ b/tools/boards.txt.py
@@ -286,7 +286,7 @@ boards = collections.OrderedDict([
             'crystalfreq_menu',
             'flashmode_dout',
             'flashfreq_40',
-            '1M',
+            '1M', '2M',
             'led',
             ],
         'desc': [ 'ESP8285 (`datasheet <http://www.espressif.com/sites/default/files/0a-esp8285_datasheet_en_v1.0_20160422.pdf>`__) is a multi-chip package which contains ESP8266 and 1MB flash. All points related to bootstrapping resistors and recommended circuits listed above apply to ESP8285 as well.',
diff --git a/tools/espota.py b/tools/espota.py
index 373020a91..d6b5a8086 100755
--- a/tools/espota.py
+++ b/tools/espota.py
@@ -132,7 +132,7 @@ def serve(remoteAddr, localAddr, remotePort, localPort, password, filename, comm
         sys.stderr.write('FAIL\n')
         logging.error('%s', data)
         sock2.close()
-        sys.exit(1);
+        sys.exit(1)
         return 1
       sys.stderr.write('OK\n')
     else:
@@ -172,7 +172,7 @@ def serve(remoteAddr, localAddr, remotePort, localPort, password, filename, comm
         connection.sendall(chunk)
         if connection.recv(32).decode().find('O') >= 0:
           # connection will receive only digits or 'OK'
-          received_ok = True;
+          received_ok = True
       except:
         sys.stderr.write('\n')
         logging.error('Error Uploading')
@@ -188,19 +188,25 @@ def serve(remoteAddr, localAddr, remotePort, localPort, password, filename, comm
     # the connection before receiving the 'O' of 'OK'
     try:
       connection.settimeout(60)
-      while not received_ok:
-        if connection.recv(32).decode().find('O') >= 0:
-          # connection will receive only digits or 'OK'
-          received_ok = True;
-      logging.info('Result: OK')
+      received_ok = False
+      received_error = False
+      while not (received_ok or received_error):
+        reply = connection.recv(64).decode()
+        # Look for either the "E" in ERROR or the "O" in OK response
+        # Check for "E" first, since both strings contain "O"
+        if reply.find('E') >= 0:
+          sys.stderr.write('\n')
+          logging.error('%s', reply)
+          received_error = True
+        elif reply.find('O') >= 0:
+          logging.info('Result: OK')
+          received_ok = True
       connection.close()
       f.close()
       sock.close()
-      if (data != "OK"):
-        sys.stderr.write('\n')
-        logging.error('%s', data)
-        return 1;
-      return 0
+      if received_ok:
+        return 0
+      return 1
     except:
       logging.error('No Result!')
       connection.close()
diff --git a/tools/platformio-build.py b/tools/platformio-build.py
index c595497cb..33ba5380f 100644
--- a/tools/platformio-build.py
+++ b/tools/platformio-build.py
@@ -247,9 +247,12 @@ else:
 #
 
 current_vtables = None
+fp_in_irom = ""
 for d in flatten_cppdefines:
     if str(d).startswith("VTABLES_IN_"):
         current_vtables = d
+    if str(d) == "FP_IN_IROM":
+        fp_in_irom = "-DFP_IN_IROM"
 if not current_vtables:
     current_vtables = "VTABLES_IN_FLASH"
     env.Append(CPPDEFINES=[current_vtables])
@@ -260,7 +263,7 @@ app_ld = env.Command(
     join("$BUILD_DIR", "ld", "local.eagle.app.v6.common.ld"),
     join(FRAMEWORK_DIR, "tools", "sdk", "ld", "eagle.app.v6.common.ld.h"),
     env.VerboseAction(
-        "$CC -CC -E -P -D%s $SOURCE -o $TARGET" % current_vtables,
+        "$CC -CC -E -P -D%s %s $SOURCE -o $TARGET" % (current_vtables, fp_in_irom),
         "Generating LD script $TARGET"))
 env.Depends("$BUILD_DIR/$PROGNAME$PROGSUFFIX", app_ld)
 
diff --git a/tools/sdk/ld/eagle.app.v6.common.ld.h b/tools/sdk/ld/eagle.app.v6.common.ld.h
index 383154e49..b7ba38e12 100644
--- a/tools/sdk/ld/eagle.app.v6.common.ld.h
+++ b/tools/sdk/ld/eagle.app.v6.common.ld.h
@@ -151,6 +151,14 @@ SECTIONS
 
     *libc.a:(.literal .text .literal.* .text.*)
     *libm.a:(.literal .text .literal.* .text.*)
+#ifdef FP_IN_IROM
+    *libgcc.a:*f2.o(.literal .text)
+    *libgcc.a:*f3.o(.literal .text)
+    *libgcc.a:*fsi.o(.literal .text)
+    *libgcc.a:*fdi.o(.literal .text)
+    *libgcc.a:*ifs.o(.literal .text)
+    *libgcc.a:*idf.o(.literal .text)
+#endif
     *libgcc.a:_umoddi3.o(.literal .text)
     *libgcc.a:_udivdi3.o(.literal .text)
     *libstdc++.a:( .literal .text .literal.* .text.*)