diff --git a/.github/workflows/githubci.yml b/.github/workflows/githubci.yml
index 68b4f7f..55086fc 100644
--- a/.github/workflows/githubci.yml
+++ b/.github/workflows/githubci.yml
@@ -21,7 +21,7 @@ jobs:
         id: set-matrix
         working-directory: src/boards
         run: |
-          MATRIX_JSON=$(ls -d */ | sed 's/\/$//' | jq -R -s -c 'split("\n")[:-1]')
+          MATRIX_JSON=$(ls -d */ | sed 's/\/$//' | grep -vE '_s340$' | jq -R -s -c 'split("\n")[:-1]')
           echo "matrix=$MATRIX_JSON"
           echo "matrix=$MATRIX_JSON" >> $GITHUB_OUTPUT
 
diff --git a/.gitignore b/.gitignore
index 1c244fc..e7b13c9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -65,3 +65,7 @@ TAGS
 
 .DS_Store
 Makefile.user
+
+# Exclude all SoftDevice S340 files
+lib/softdevice/s340*
+
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 567a815..6d21fa6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -227,22 +227,37 @@ if (MCU_VARIANT STREQUAL "nrf52")
     S132
     )
 elseif (MCU_VARIANT STREQUAL "nrf52833")
-  set(SD_NAME s140)
   set(DFU_DEV_REV 52833)
   set(DFU_APP_DATA_RESERVED 7*4096)
-  target_compile_definitions(bootloader PUBLIC
-    NRF52833_XXAA
-    S140
-    )
+  if (SD_NAME STREQUAL "s340")
+    target_compile_definitions(bootloader PUBLIC
+      NRF52833_XXAA
+      S340
+      )
+  else ()
+    set(SD_NAME s140)
+    target_compile_definitions(bootloader PUBLIC
+      NRF52833_XXAA
+      S140
+      )
+  endif ()
 elseif (MCU_VARIANT STREQUAL "nrf52840")
-  set(SD_NAME s140)
   set(DFU_DEV_REV 52840)
   # App reserved 40KB (8+32) to match circuitpython for 840
   set(DFU_APP_DATA_RESERVED 10*4096)
-  target_compile_definitions(bootloader PUBLIC
-    NRF52840_XXAA
-    S140
-    )
+  if (SD_NAME STREQUAL "s340")
+    target_compile_definitions(bootloader PUBLIC
+      NRF52840_XXAA
+      S340
+      )
+  else ()
+    set(SD_NAME s140)
+    target_compile_definitions(bootloader PUBLIC
+      NRF52840_XXAA
+      S140
+      )
+  endif ()
+
 else ()
   message(FATAL_ERROR "MCU_VARIANT ${MCU_VARIANT} is unknown")
 endif ()
diff --git a/Makefile b/Makefile
index f345826..22ad007 100644
--- a/Makefile
+++ b/Makefile
@@ -109,14 +109,22 @@ ifeq ($(MCU_SUB_VARIANT),nrf52)
   CFLAGS += -DNRF52 -DNRF52832_XXAA -DS132
   DFU_APP_DATA_RESERVED=7*4096
 else ifeq ($(MCU_SUB_VARIANT),nrf52833)
-  SD_NAME = s140
+  ifeq ($(SD_NAME),s340)
+    CFLAGS += -DNRF52833_XXAA -DS340
+  else
+	SD_NAME = s140
+    CFLAGS += -DNRF52833_XXAA -DS140
+  endif
   DFU_DEV_REV = 52833
-  CFLAGS += -DNRF52833_XXAA -DS140
   DFU_APP_DATA_RESERVED=7*4096
 else ifeq ($(MCU_SUB_VARIANT),nrf52840)
-  SD_NAME = s140
+  ifeq ($(SD_NAME),s340)
+    CFLAGS += -DNRF52840_XXAA -DS340
+  else
+	SD_NAME = s140
+    CFLAGS += -DNRF52840_XXAA -DS140
+  endif
   DFU_DEV_REV = 52840
-  CFLAGS += -DNRF52840_XXAA -DS140
   # App reserved 40KB (8+32) to match circuitpython for 840
   DFU_APP_DATA_RESERVED=10*4096
 else
diff --git a/README.md b/README.md
index b4e3cdb..ce2ab06 100644
--- a/README.md
+++ b/README.md
@@ -137,6 +137,25 @@ Supported boards are: feather_nrf52840_express feather_nrf52840_express pca10056
 Makefile:90: *** BOARD not defined.  Stop
 ```
 
+#### Working with SoftDevice S340:
+The SoftDevice S340 is closed-source, not publicly available and is only distributed by Garmin Canada Inc.  
+
+In order to be able to download the required ANT+ capable SoftDevice, you need to register an 'ANT+ Adopter' account at [thisisant.com](https://www.thisisant.com/register/). After around one business day you will receive access to the resources there. Then do the following steps:
+- Download the SoftDevice S340 v7.0.1 [(here)](https://www.thisisant.com/developer/components/nrf52832#tab_protocol_stacks_tab) and extract its contents
+- Under `lib/softdevice` in this repository there is a folder called `s340_nrf52_7.0.1`
+  - Copy the API folder `ANT_s340_nrf52_7.0.1.API`, the license agreement `License_Agreement_ANT_Softdevice_rev3_3.pdf` and the hex file `ANT_s340_nrf52_7.0.1.hex` from the extracted contents to it.
+  - Rename the API folder to `s340_nrf52_7.0.1_API`
+  - Rename the hex file to `s340_nrf52_7.0.1_softdevice.hex`
+  - Modify `lib/softdevice/s340_nrf52_7.0.1_API/include/nrf_sdm.h` on line 191 and remove the two slashes at the beginning of `//#define...` to use the *evaluation key* for the ANT SoftDevice.
+  - **VERY IMPORTANT:** You MUST obtain a valid commercial license key BEFORE releasing a product to market that uses the ANT SoftDevice!
+
+To add or modify a board with an ANT+ capable SoftDevice S340 the `SD_VERSION` and `SD_NAME` parameters in the corresponding `board.mk` file have to be set:
+```
+SD_VERSION = 7.0.1
+SD_NAME = s340
+```
+**Important:** When adding a new board you must add the suffix `_s340` to the folder name to exclude it from automatic builds.
+
 ### Flash
 
 To flash the bootloader (without softdevice/mbr) using JLink:
diff --git a/lib/softdevice/s340_nrf52_7.0.1/readme.txt b/lib/softdevice/s340_nrf52_7.0.1/readme.txt
new file mode 100644
index 0000000..3cde0e6
--- /dev/null
+++ b/lib/softdevice/s340_nrf52_7.0.1/readme.txt
@@ -0,0 +1 @@
+Place SoftDevice S340 v7.0.1 files here
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index 92ad020..b48e1cb 100644
--- a/src/main.c
+++ b/src/main.c
@@ -157,6 +157,14 @@ static void mbr_init_sd(void) {
   sd_mbr_command(&com);
 }
 
+// Helper function to check if SoftDevice is already enabled.
+// Especially SoftDevice S340 locks up when calling sd_softdevice_disable() and it's not enabled.
+static bool is_sd_enabled(void) {
+  uint8_t sd_enabled = 0;
+  sd_softdevice_is_enabled(&sd_enabled);
+  return (sd_enabled == 1);
+}
+
 //--------------------------------------------------------------------+
 //
 //--------------------------------------------------------------------+
@@ -206,13 +214,16 @@ int main(void) {
       if (!_sd_inited) mbr_init_sd();
 
       // Make sure SD is disabled
-      sd_softdevice_disable();
+      if (is_sd_enabled()) {
+        sd_softdevice_disable();
+      }
     }
 
     // clear in case we kept DFU_DBL_RESET_APP there
     (*dbl_reset_mem) = 0;
 
     // start application
+    PRINTF("Starting app...\r\n");
     bootloader_app_start();
   }
 
@@ -306,7 +317,9 @@ static void check_dfu_mode(void) {
     }
 
     if (_ota_dfu) {
-      sd_softdevice_disable();
+      if (is_sd_enabled()) {
+        sd_softdevice_disable();
+      }
     } else {
       usb_teardown();
     }
@@ -326,7 +339,11 @@ static uint32_t ble_stack_init(void) {
       .rc_temp_ctiv = 2,
       .accuracy     = NRF_CLOCK_LF_ACCURACY_250_PPM
   };
-  sd_softdevice_enable(&clock_cfg, app_error_fault_handler);
+  #ifndef ANT_LICENSE_KEY
+    sd_softdevice_enable(&clock_cfg, app_error_fault_handler);
+  #else
+    sd_softdevice_enable(&clock_cfg, app_error_fault_handler, ANT_LICENSE_KEY);
+  #endif
   sd_nvic_EnableIRQ(SD_EVT_IRQn);
 
   /*------------- Configure BLE params  -------------*/