diff --git a/.gitignore b/.gitignore
index cd45f94..e560edd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+.pio
 .config
 *.o
 *.pyc
@@ -41,4 +42,4 @@ build
 dependencies.lock
 
 sdkconfig
-sdkconfig.old
\ No newline at end of file
+sdkconfig.old
diff --git a/include/README b/include/README
new file mode 100644
index 0000000..194dcd4
--- /dev/null
+++ b/include/README
@@ -0,0 +1,39 @@
+
+This directory is intended for project header files.
+
+A header file is a file containing C declarations and macro definitions
+to be shared between several project source files. You request the use of a
+header file in your project source file (C, C++, etc) located in `src` folder
+by including it, with the C preprocessing directive `#include'.
+
+```src/main.c
+
+#include "header.h"
+
+int main (void)
+{
+ ...
+}
+```
+
+Including a header file produces the same results as copying the header file
+into each source file that needs it. Such copying would be time-consuming
+and error-prone. With a header file, the related declarations appear
+in only one place. If they need to be changed, they can be changed in one
+place, and programs that include the header file will automatically use the
+new version when next recompiled. The header file eliminates the labor of
+finding and changing all the copies as well as the risk that a failure to
+find one copy will result in inconsistencies within a program.
+
+In C, the usual convention is to give header files names that end with `.h'.
+It is most portable to use only letters, digits, dashes, and underscores in
+header file names, and at most one dot.
+
+Read more about using header files in official GCC documentation:
+
+* Include Syntax
+* Include Operation
+* Once-Only Headers
+* Computed Includes
+
+https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html
diff --git a/include/mbedtls+HKDF.h b/include/mbedtls+HKDF.h
new file mode 100644
index 0000000..28dfd8b
--- /dev/null
+++ b/include/mbedtls+HKDF.h
@@ -0,0 +1,16 @@
+/**
+ * \def MBEDTLS_HKDF_C
+ *
+ * Disable the HKDF algorithm (RFC 5869).
+ *
+ * Module:  library/hkdf.c
+ * Caller:
+ *
+ * Requires: MBEDTLS_MD_C
+ *
+ * This module adds support for the Hashed Message Authentication Code
+ * (HMAC)-based key derivation function (HKDF).
+ */
+#ifndef MBEDTLS_HKDF_C
+#define MBEDTLS_HKDF_C
+#endif
diff --git a/lib/README b/lib/README
new file mode 100644
index 0000000..6debab1
--- /dev/null
+++ b/lib/README
@@ -0,0 +1,46 @@
+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into executable file.
+
+The source code of each library should be placed in a an own separate directory
+("lib/your_library_name/[here are source files]").
+
+For example, see a structure of the following two libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional, custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+and a contents of `src/main.c`:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+PlatformIO Library Dependency Finder will find automatically dependent
+libraries scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html
diff --git a/main/CMakeLists.txt b/main/CMakeLists.txt
index 281f413..d625c26 100644
--- a/main/CMakeLists.txt
+++ b/main/CMakeLists.txt
@@ -2,6 +2,6 @@ idf_component_register(
     SRCS 
         "main.c"
         "display-interface.c"
-        "wifi.c"
+        "wifi/espidf-v4.0.c"
     INCLUDE_DIRS ""
 )
diff --git a/main/wifi.c b/main/wifi/espidf-v4.1.c
similarity index 99%
rename from main/wifi.c
rename to main/wifi/espidf-v4.1.c
index 3a860e5..a6a0a8f 100644
--- a/main/wifi.c
+++ b/main/wifi/espidf-v4.1.c
@@ -1,3 +1,4 @@
+#ifdef FRAMEWORK_espidf
 // Copyright 2020 Lukas Haubaum
 //
 // Licensed under the GNU Affero General Public License, Version 3;
@@ -169,4 +170,5 @@ void wifi_start(void)
 bool wifi_is_connected(void)
 {
     return connected;
-}
\ No newline at end of file
+}
+#endif
diff --git a/main/wifi/zephyr.c b/main/wifi/zephyr.c
new file mode 100644
index 0000000..a560f8d
--- /dev/null
+++ b/main/wifi/zephyr.c
@@ -0,0 +1,3 @@
+#ifdef FRAMEWORK_zephyr
+#error WIFI not implemented, yet
+#endif
diff --git a/platformio.ini b/platformio.ini
new file mode 100644
index 0000000..6d98398
--- /dev/null
+++ b/platformio.ini
@@ -0,0 +1,70 @@
+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[platformio]
+src_dir = main
+
+[env]
+build_flags = 
+    -Iinclude/tls_config
+    -DFRAMEWORK_$PIOFRAMEWORK
+
+[env:esp32dev]
+platform = espressif32
+framework = espidf
+board = esp32dev
+build_flags = 
+    ${env.build_flags}
+    -Iinclude
+    -DMBEDTLS_USER_CONFIG_FILE=\"mbedtls+HKDF.h\"
+board_build.embed_files =
+    components/ena/test/export.bin
+    components/ena-cwa/certs/telekom.pem
+
+
+[env:ID107HR]
+platform = nordicnrf51
+board = ng_beacon ; tbd
+framework = zephyr
+monitor_speed = 115200
+test_ignore = test_desktop
+build_flags = 
+    ${env.build_flags}
+    # For testing: -DUNITY_EXCLUDE_SETJMP_H=1
+    -DEN_INCLUDE_ZEPHYR_DEPS=1
+    -DEN_INIT_MBEDTLS_ENTROPY=0
+lib_deps = exposure-notification
+
+[env:nrf52840_dk]
+platform = nordicnrf52
+board = nrf52840_dk
+framework = zephyr
+monitor_speed = 115200
+test_ignore = test_desktop
+build_flags = 
+    ${env.build_flags}
+    # For testing: -DUNITY_EXCLUDE_SETJMP_H=1
+    -DEN_INCLUDE_ZEPHYR_DEPS=1
+    -DEN_INIT_MBEDTLS_ENTROPY=0
+lib_deps = exposure-notification
+
+    
+[env:desktop]
+platform = native
+test_ignore = test_embedded
+lib_compat_mode = off
+lib_deps = mbedtls@~2
+build_flags = 
+    ${env.build_flags}
+    -Iinclude/desktop
+    -Wno-nullability-completeness
+    -DMBEDTLS_USER_CONFIG_FILE='"user-tls.conf"'
+src_filter = --<.src/>   
+targets = test
diff --git a/test/README b/test/README
new file mode 100644
index 0000000..df5066e
--- /dev/null
+++ b/test/README
@@ -0,0 +1,11 @@
+
+This directory is intended for PIO Unit Testing and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PIO Unit Testing:
+- https://docs.platformio.org/page/plus/unit-testing.html
diff --git a/zephyr/CMakeLists.txt b/zephyr/CMakeLists.txt
new file mode 100644
index 0000000..67128aa
--- /dev/null
+++ b/zephyr/CMakeLists.txt
@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.13.1)
+include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
+project(esp-ena)
+
+FILE(GLOB app_sources ../src/*.c*)
+target_sources(app PRIVATE ${app_sources})