Sorry... wrong platformio.ini used (it should be dev branch instead master)

platformio.ini

@@ -9,6 +9,7 @@
 
 [platformio]
 src_dir = sonoff
+build_dir = .pioenvs
 
 ; *** Uncomment one of the lines below to build/upload only one environment
 ;env_default = sonoff
@@ -99,8 +100,10 @@ build_flags               = ${esp82xx_defaults.build_flags}
 ; Code optimization see https://github.com/esp8266/Arduino/issues/5790#issuecomment-475672473
                             -O2
                             -DBEARSSL_SSL_BASIC
+; nonos-sdk 22y
+                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK22y
 ; nonos-sdk 22x
-                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK22x
+;                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK22x
 ; nonos-sdk-pre-v3
 ;                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK3
 ; lwIP 1.4
@@ -127,16 +130,55 @@ build_flags               = ${esp82xx_defaults.build_flags}
 ;                           -fexceptions
 ;                           -lstdc++-exc
 
+[core_pre]
+; *** Arduino Esp8266 core pre 2.6.x for Tasmota (mqtt reconnects fixed)
+platform                  = https://github.com/Jason2866/platform-espressif8266.git#Tasmota
+build_flags               = ${esp82xx_defaults.build_flags}
+                            -Wl,-Tesp8266.flash.1m.ld
+                            -O2
+                            -DBEARSSL_SSL_BASIC
+; nonos-sdk 22y
+                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK22y
+; nonos-sdk 22x
+;                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK22x
+; nonos-sdk-pre-v3
+;                            -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK3
+; lwIP 1.4
+;                            -DPIO_FRAMEWORK_ARDUINO_LWIP_HIGHER_BANDWIDTH
+; lwIP 2 - Low Memory
+;                            -DPIO_FRAMEWORK_ARDUINO_LWIP2_LOW_MEMORY
+; lwIP 2 - Higher Bandwidth
+;                            -DPIO_FRAMEWORK_ARDUINO_LWIP2_HIGHER_BANDWIDTH
+; lwIP 2 - Higher Bandwitdh Low Memory no Features
+;                            -DPIO_FRAMEWORK_ARDUINO_LWIP2_LOW_MEMORY_LOW_FLASH
+; lwIP 2 - Higher Bandwitdh no Features
+                            -DPIO_FRAMEWORK_ARDUINO_LWIP2_HIGHER_BANDWIDTH_LOW_FLASH
+; VTABLES in Flash (default)
+                            -DVTABLES_IN_FLASH
+; VTABLES in Heap
+;                            -DVTABLES_IN_DRAM
+; VTABLES in IRAM
+;                            -DVTABLES_IN_IRAM
+; enable one option set -> No exception recommended
+; No exception code in firmware
+                            -fno-exceptions
+                            -lstdc++
+; Exception code in firmware /needs much space!
+;                           -fexceptions
+;                           -lstdc++-exc
+
 [core_active]
 ; Select one core set for platform and build_flags
-platform                  = ${core_2_3_0.platform}
+;platform                  = ${core_2_3_0.platform}
-build_flags               = ${core_2_3_0.build_flags}
+;build_flags               = ${core_2_3_0.build_flags}
 ;platform                  = ${core_2_4_2.platform}
 ;build_flags               = ${core_2_4_2.build_flags}
-;platform                  = ${core_2_5_2.platform}
+platform                  = ${core_2_5_2.platform}
-;build_flags               = ${core_2_5_2.build_flags}
+build_flags               = ${core_2_5_2.build_flags}
 ;platform                  = ${core_stage.platform}
 ;build_flags               = ${core_stage.build_flags}
+;platform                  = ${core_pre.platform}
+;build_flags               = ${core_pre.build_flags}
 
 [common]
 framework                 = arduino